Brian Koberleinhttps://briankoberlein.com/Recent content by Brian Koberleinen-usThis work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International LicenseTue, 26 Mar 2024 09:36:45 +0000Brilliant Mergerhttps://briankoberlein.com/blog/brilliant-merger/Tue, 26 Mar 2024 09:36:45 +0000https://briankoberlein.com/blog/brilliant-merger/ <figure class=""> <a href="https://briankoberlein.com/blog/brilliant-merger/stars.jpg"> <span class="credit"> <img srcset=' /blog/brilliant-merger/stars_hu94dab00f2bef5820f285533ae1fc390e_159685_300x0_resize_q75_box.jpg 300w , /blog/brilliant-merger/stars_hu94dab00f2bef5820f285533ae1fc390e_159685_550x0_resize_q75_box.jpg 550w , /blog/brilliant-merger/stars_hu94dab00f2bef5820f285533ae1fc390e_159685_700x0_resize_q75_box.jpg 700w , /blog/brilliant-merger/stars_hu94dab00f2bef5820f285533ae1fc390e_159685_900x0_resize_q75_box.jpg 900w , /blog/brilliant-merger/stars_hu94dab00f2bef5820f285533ae1fc390e_159685_1100x0_resize_q75_box.jpg 1100w ' src="https://briankoberlein.com/blog/brilliant-merger/stars_hu94dab00f2bef5820f285533ae1fc390e_159685_300x0_resize_q75_box.jpg" loading="lazy" width="1280" height="747" alt="Artistic image of a binary system of a red giant star and a younger companion that can merge to produce a blue supergiant."/> <span class="attribution">Casey Reed, NASA</span></span> </a> <figcaption>Artistic image of a binary system of a red giant star and a younger companion that can merge to produce a blue supergiant.</figcaption> </figure> <p>In the constellation of Orion, there is a brilliant bluish-white star. It marks the right foot of the starry hunter. It&rsquo;s known as Rigel, and it is the most famous example of a blue supergiant star. Blue supergiants are more than 10,000 times brighter than the Sun, with masses 16 - 40 times greater. They are unstable and short-lived, so they should be rare in the galaxy. While they are rare, blue supergiants aren&rsquo;t as rare as we would expect. A new study may have figured out why.<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup></p> <p>We aren&rsquo;t entirely sure how these massive stars form, though one idea is that they occur when a massive main sequence star passes through an interstellar cloud. By capturing gas and dust from the cloud, a star can shift off the main sequence to become a blue supergiant. Another idea is that they may form within stellar nurseries with a mass as great as 300 Suns. As a result, they quickly burn so brightly that they never become true main-sequence stars. Both of these models predict that blue supergiants are much more rare than the number we observe.</p> <p>This new study starts by noting that blue supergiants, particularly the smaller ones known as B-type supergiants, are rarely seen with companion stars. This is odd since most massive stars form as part of a binary or multiple system. The authors propose that B-type blue supergiants aren&rsquo;t often in binary systems because they typically are the product of binary mergers.</p> <p>The team simulated a range of models where a giant main-sequence star has a smaller close-orbiting companion and then looked at what would result if the two stars merged. They then compared the results to observations of 59 young blue supergiant stars in the Large Magellanic Cloud. They found that not only can these mergers produce blue supergiants in the mass range of the Magellanic stars, but the spectra of the simulated mergers match the spectra of the 59 blue supergiants. This strongly suggests that many if not most B-type blue supergiants are the result of stellar mergers.</p> <p>In the future, the team would like to carry this work further to see how blue supergiants evolve into neutron stars and black holes. This could help explain the type of mergers observed by gravitational wave observatories such as LIGO and Virgo.</p> <div class="footnotes" role="doc-endnotes"> <hr> <ol> <li id="fn:1"> <p>Menon, Athira, et al. &ldquo;Evidence for Evolved Stellar Binary Mergers in Observed B-type Blue Supergiants.&rdquo; <em>The Astrophysical Journal Letters</em> 963.2 (2024): L42.&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> </ol> </div>A Dwarf's Dark Talehttps://briankoberlein.com/blog/dwarfs-dark-tale/Mon, 25 Mar 2024 14:30:10 +0000https://briankoberlein.com/blog/dwarfs-dark-tale/ <figure class=""> <a href="https://briankoberlein.com/blog/dwarfs-dark-tale/dwarf.jpg"> <span class="credit"> <img srcset=' /blog/dwarfs-dark-tale/dwarf_hu53f3c98229dfe4ee6e2f067dbeafff22_395632_300x0_resize_q75_box.jpg 300w , /blog/dwarfs-dark-tale/dwarf_hu53f3c98229dfe4ee6e2f067dbeafff22_395632_550x0_resize_q75_box.jpg 550w , /blog/dwarfs-dark-tale/dwarf_hu53f3c98229dfe4ee6e2f067dbeafff22_395632_700x0_resize_q75_box.jpg 700w , /blog/dwarfs-dark-tale/dwarf_hu53f3c98229dfe4ee6e2f067dbeafff22_395632_900x0_resize_q75_box.jpg 900w , /blog/dwarfs-dark-tale/dwarf_hu53f3c98229dfe4ee6e2f067dbeafff22_395632_1100x0_resize_q75_box.jpg 1100w , /blog/dwarfs-dark-tale/dwarf_hu53f3c98229dfe4ee6e2f067dbeafff22_395632_1400x0_resize_q75_box.jpg 1400w , /blog/dwarfs-dark-tale/dwarf_hu53f3c98229dfe4ee6e2f067dbeafff22_395632_1800x0_resize_q75_box.jpg 1800w ' src="https://briankoberlein.com/blog/dwarfs-dark-tale/dwarf_hu53f3c98229dfe4ee6e2f067dbeafff22_395632_300x0_resize_q75_box.jpg" loading="lazy" width="2200" height="1500" alt="Dark matter map in Galaxy Cluster Abell 1689."/> <span class="attribution">NASA, ESA, and D. Coe (NASA JPL/Caltech and STScI)</span></span> </a> <figcaption>Dark matter map in Galaxy Cluster Abell 1689.</figcaption> </figure> <p>If you have a view of the southern celestial sky, on a clear night you might see two clear smudges of light set off a bit from the great arch of the Milky Way. They are the Large and Small Magellanic Clouds, and they are the most visible of the dwarf galaxies. Dwarf galaxies are small galaxies that typically cluster around larger ones. The Milky Way, for example, has nearly two dozen dwarf galaxies. Because of their small size, they can be more significantly affected by dark matter. Their formation may even have been triggered by the distribution of dark matter. So they can be an excellent way to study this mysterious unseen material.</p> <p>In a recent study, a team looked at dwarf galaxies to see exactly what they would reveal about dark matter.<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup> Specifically, they were interested in how dark matter might interact with itself. One idea about dark matter particles is that when they collide with each other they could emit gamma-ray light. This would mean that the central regions of galaxies should show evidence of gamma radiation without a clear astrophysical source. There have been <a href="https://briankoberlein.com/blog/when-dark-matter-collides/">some studies looking for gamma rays within our own galaxy,</a> but the <a href="https://briankoberlein.com/blog/annihilating-a-theory/">results have been inconclusive.</a></p> <p>This new study focused on dwarf galaxies because they are smaller and therefore less likely to obscure gamma-ray light from colliding dark matter. There are also plenty of dwarf galaxies within our local group. Using 14 years of archival data from the Fermi-Large Area Telescope (LAT), the team looked at 50 dwarf galaxies. Overall they didn&rsquo;t find strong evidence of gamma-ray emissions from any of the galaxies, but in 7 of them they found a small statistical excess at around 2σ - 3σ. To be definitive we&rsquo;d like to see it at a level of 5σ, so this result is far from conclusive. But if we take the energy levels of the excess at face value, it would put the mass of dark matter particles around 30 - 50 GeV or 150 − 230 GeV, depending on the way dark matter might decay. By comparison, protons have a mass of about 1 GeV.</p> <p>So once again a study of dark matter fails to discover the elusive particles. But as with earlier studies, this research narrows down what dark matter might be. Specifically, the study rules out certain mass ranges for dark matter more than ever before. It&rsquo;s yet another small step toward solving the mystery of dark matter.</p> <div class="footnotes" role="doc-endnotes"> <hr> <ol> <li id="fn:1"> <p>McDaniel, Alex, et al. &ldquo;Legacy analysis of dark matter annihilation from the Milky Way dwarf spheroidal galaxies with 14 years of Fermi-LAT data.&rdquo; <em>Physical Review D</em> 109.6 (2024): 063024.&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> </ol> </div>The Alien Factorhttps://briankoberlein.com/blog/alien-factor/Wed, 13 Mar 2024 10:22:25 +0000https://briankoberlein.com/blog/alien-factor/ <figure class=""> <a href="https://briankoberlein.com/blog/alien-factor/spherule.jpg"> <span class="credit"> <img srcset=' /blog/alien-factor/spherule_hu7f196308853ac70bc620c9bfecab452d_376140_300x0_resize_q75_box.jpg 300w , /blog/alien-factor/spherule_hu7f196308853ac70bc620c9bfecab452d_376140_550x0_resize_q75_box.jpg 550w , /blog/alien-factor/spherule_hu7f196308853ac70bc620c9bfecab452d_376140_700x0_resize_q75_box.jpg 700w , /blog/alien-factor/spherule_hu7f196308853ac70bc620c9bfecab452d_376140_900x0_resize_q75_box.jpg 900w , /blog/alien-factor/spherule_hu7f196308853ac70bc620c9bfecab452d_376140_1100x0_resize_q75_box.jpg 1100w , /blog/alien-factor/spherule_hu7f196308853ac70bc620c9bfecab452d_376140_1400x0_resize_q75_box.jpg 1400w ' src="https://briankoberlein.com/blog/alien-factor/spherule_hu7f196308853ac70bc620c9bfecab452d_376140_300x0_resize_q75_box.jpg" loading="lazy" width="1500" height="843" alt="A 0.4-millimeter diameter iron-rich spherule."/> <span class="attribution">Avi Loeb/The Galileo Project</span></span> </a> <figcaption>A 0.4-millimeter diameter iron-rich spherule.</figcaption> </figure> <p>Our solar system does not exist in isolation. It formed within a stellar nursery along with hundreds of sibling stars, and even today has the occasional interaction with interstellar objects such as <a href="https://briankoberlein.com/blog/it-came-from-beyond/">Oumuamua and Borisov.</a> So it&rsquo;s reasonable to presume that some interstellar material has reached Earth. Recently Avi Loeb and his team earned quite a bit of attention with a study arguing that it had found some of this interstellar stuff on the ocean seabed.<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup> But a new study finds that the material has a much more local origin.<sup id="fnref:2"><a href="#fn:2" class="footnote-ref" role="doc-noteref">2</a></sup></p> <p>The original study is based on a 2014 meteor that entered the Earth&rsquo;s atmosphere off the coast of Papua New Guinea. Observations of its impact trajectory suggested it might have been extraterrestrial in origin. And since we had an idea of where it hit, why not look for its debris? This led Loeb&rsquo;s team to the seafloor near Papua New Guinea, where they found small, iron-rich spheres known as spherules. The study analyzed the composition of these spherules and found the isotope distribution was so unusual they must have an interstellar origin.</p> <figure class="right"> <a href="https://briankoberlein.com/blog/alien-factor/origin.jpg"> <span class="credit"> <img srcset=' /blog/alien-factor/origin_hu72536bc3b8e60a5b63a095ef64c75739_100534_300x0_resize_q75_box.jpg 300w , /blog/alien-factor/origin_hu72536bc3b8e60a5b63a095ef64c75739_100534_350x0_resize_q75_box.jpg 350w , /blog/alien-factor/origin_hu72536bc3b8e60a5b63a095ef64c75739_100534_550x0_resize_q75_box.jpg 550w , /blog/alien-factor/origin_hu72536bc3b8e60a5b63a095ef64c75739_100534_600x0_resize_q75_box.jpg 600w , /blog/alien-factor/origin_hu72536bc3b8e60a5b63a095ef64c75739_100534_700x0_resize_q75_box.jpg 700w , /blog/alien-factor/origin_hu72536bc3b8e60a5b63a095ef64c75739_100534_1100x0_resize_q75_box.jpg 1100w ' src="https://briankoberlein.com/blog/alien-factor/origin_hu72536bc3b8e60a5b63a095ef64c75739_100534_300x0_resize_q75_box.jpg" loading="lazy" width="1588" height="966" alt="The iron isotopes of these spherules show a local origin."/> <span class="attribution">Desch, et al</span></span> </a> <figcaption>The iron isotopes of these spherules show a local origin.</figcaption> </figure> <p>While that sounds compelling, there are a few caveats. The first is that the trajectory of the 2014 meteor isn&rsquo;t that precisely known. We know the general impact region, but the data simply isn&rsquo;t good enough to prove that these spherules came from this particular meteor. The second is that &ldquo;unusual&rdquo; isotopes aren&rsquo;t uncommon within our solar system. As the new study shows, there is a distribution of iron isotope ratios for objects originating in the solar system, specifically the ratios of <sup>57</sup>Fe and <sup>56</sup>Fe. The ratio for the &ldquo;alien&rdquo; spherules is well within that range. So well that the odds of them being interstellar is less than 1 in 10,000. So these spherules have a local origin.</p> <p>But they were likely formed from an impact event, so this new study went further. Is there a known impact from which these spherules originated? Turns out there is. The region in which they were found is part of what&rsquo;s known as the Australasian tektite strewn field. It is a vast field that spans southeast Asia to Antarctica and was caused by a large impact 790,000 years ago. The team looked at other isotope ratios and found they are consistent with other known Australasian tektites.</p> <p>So these particular spherules have a local origin. But that doesn&rsquo;t mean interstellar meteorites don&rsquo;t exist. Given what we know, there are almost certainly interstellar objects on Earth just waiting to be found. We just have to keep looking for them.</p> <div class="footnotes" role="doc-endnotes"> <hr> <ol> <li id="fn:1"> <p>Loeb, A., et al. &ldquo;Recovery and Classification of Spherules from the Pacific Ocean Site of the CNEOS 2014 January 8 (IM1) Bolide.&rdquo; <em>Research Notes of the AAS</em> 8.1 (2024): 39.&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> <li id="fn:2"> <p>Desch, Steve. &ldquo;Be, La, U-rich spherules as microtektites of terrestrial laterites: What goes up must come down.&rdquo; <em>arXiv preprint</em> arXiv:2403.05161 (2024).&#160;<a href="#fnref:2" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> </ol> </div>The Pause That Refresheshttps://briankoberlein.com/blog/pause-that-refreshes/Mon, 11 Mar 2024 13:12:18 +0000https://briankoberlein.com/blog/pause-that-refreshes/ <figure class=""> <a href="https://briankoberlein.com/blog/pause-that-refreshes/merger.jpg"> <span class="credit"> <img srcset=' /blog/pause-that-refreshes/merger_hu811c86b887edf7e5d0e1d438d3007b68_136941_300x0_resize_q75_box.jpg 300w , /blog/pause-that-refreshes/merger_hu811c86b887edf7e5d0e1d438d3007b68_136941_550x0_resize_q75_box.jpg 550w , /blog/pause-that-refreshes/merger_hu811c86b887edf7e5d0e1d438d3007b68_136941_700x0_resize_q75_box.jpg 700w , /blog/pause-that-refreshes/merger_hu811c86b887edf7e5d0e1d438d3007b68_136941_900x0_resize_q75_box.jpg 900w ' src="https://briankoberlein.com/blog/pause-that-refreshes/merger_hu811c86b887edf7e5d0e1d438d3007b68_136941_300x0_resize_q75_box.jpg" loading="lazy" width="1024" height="576" alt="A pair of disc galaxies in the late stages of a merger."/> <span class="attribution">NASA</span></span> </a> <figcaption>A pair of disc galaxies in the late stages of a merger.</figcaption> </figure> <p>The Universe is filled with supermassive black holes. Almost every galaxy in the cosmos has one, and they are the most well-studied black holes by astronomers. But one thing we still don&rsquo;t understand is just how they grew so massive so quickly. To answer that, astronomers have to identify lots of black holes in the early Universe, and since they are typically found in merging galaxies, that means astronomers have to identify early galaxies accurately. By hand. But thanks to the power of machine learning, that&rsquo;s changing.<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup></p> <p>With the power of current and future sky surveys, the challenge of astronomy is less about capturing the right data and more about filtering out the right data from the vast trove we gather. It takes a tremendous amount of skill to distinguish a true merging galaxy from an irregular galaxy or two independent galaxies that just happen to be seen in the same patch of sky. People can be trained to do it well, but the need for skilled identifiers far surpasses the number of skilled people. One way to overcome this is to allow volunteers to fill the gap. In general, their identifications won&rsquo;t be as accurate as the professionals, but a bit of statistics will allow astronomers to glean useful information.</p> <figure class="right"> <a href="https://briankoberlein.com/blog/pause-that-refreshes/identification.jpg"> <span class="credit"> <img srcset=' /blog/pause-that-refreshes/identification_hu30adda31177b37cf268f3440718ac620_188315_300x0_resize_q75_box.jpg 300w , /blog/pause-that-refreshes/identification_hu30adda31177b37cf268f3440718ac620_188315_350x0_resize_q75_box.jpg 350w , /blog/pause-that-refreshes/identification_hu30adda31177b37cf268f3440718ac620_188315_550x0_resize_q75_box.jpg 550w , /blog/pause-that-refreshes/identification_hu30adda31177b37cf268f3440718ac620_188315_600x0_resize_q75_box.jpg 600w , /blog/pause-that-refreshes/identification_hu30adda31177b37cf268f3440718ac620_188315_700x0_resize_q75_box.jpg 700w , /blog/pause-that-refreshes/identification_hu30adda31177b37cf268f3440718ac620_188315_1100x0_resize_q75_box.jpg 1100w ' src="https://briankoberlein.com/blog/pause-that-refreshes/identification_hu30adda31177b37cf268f3440718ac620_188315_300x0_resize_q75_box.jpg" loading="lazy" width="1851" height="1458" alt="True positives vs false positives in machine learning identification."/> <span class="attribution">Avirett-Mackenzie, et al</span></span> </a> <figcaption>True positives vs false positives in machine learning identification.</figcaption> </figure> <p>This new study takes a different approach. Rather than having experts train volunteers, they used experts to train machine learning algorithms. That&rsquo;s easier said than done. Even the most skilled expert will occasionally make mistakes, or have certain biases, and any software trained on that expert will have the same biases. So the team partnered with the Big Data Applications for Black Hole Evolution Studies (BiD4BEST), which is an EU project that provides a training network for black hole evolution data. Together they used skilled experts to identify black hole mergers in both simulated data and data from the Sloan Digital Sky Survey (SDSS). By comparing the two, the team could remove biases from the machine learning data. The result was pretty successful. When algorithm sortings were compared to simulated mergers they found it had an accuracy of well over 80%, comparable to that of the most skilled experts.</p> <p>The team then used the software to identify more than 8,000 active black holes and found an interesting connection between the growth of black holes and their galaxies. It isn&rsquo;t galactic mergers that trigger the growth of supermassive black holes, but large quantities of nearby cold gas. The team found that mergers only drive rapid growth when they involve the merger of star-forming galaxies rich in gas and dust. Thus, the same conditions that lead to star formation also lead to supermassive black holes. This is part of the reason why galaxies and their black holes seem to grow in parallel.</p> <p>As we continue to capture astronomical data at an almost exponential rate, software will be a necessary complement to skilled observers. As this study shows, the two can be used together effectively.</p> <div class="footnotes" role="doc-endnotes"> <hr> <ol> <li id="fn:1"> <p>Avirett-Mackenzie, M. S., et al. &ldquo;A post-merger enhancement only in star-forming Type 2 Seyfert galaxies: the deep learning view.&rdquo; <em>Monthly Notices of the Royal Astronomical Society</em> 528.4 (2024): 6915-6933.&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> </ol> </div>How to Stay Hot as You Agehttps://briankoberlein.com/blog/how-to-stay-hot/Sat, 09 Mar 2024 09:53:41 +0000https://briankoberlein.com/blog/how-to-stay-hot/ <figure class=""> <a href="https://briankoberlein.com/blog/how-to-stay-hot/crystals.jpg"> <span class="credit"> <img srcset=' /blog/how-to-stay-hot/crystals_hue94aa6a75956f8f2b955e208599b77d8_414645_300x0_resize_q75_box.jpg 300w , /blog/how-to-stay-hot/crystals_hue94aa6a75956f8f2b955e208599b77d8_414645_550x0_resize_q75_box.jpg 550w , /blog/how-to-stay-hot/crystals_hue94aa6a75956f8f2b955e208599b77d8_414645_700x0_resize_q75_box.jpg 700w , /blog/how-to-stay-hot/crystals_hue94aa6a75956f8f2b955e208599b77d8_414645_900x0_resize_q75_box.jpg 900w , /blog/how-to-stay-hot/crystals_hue94aa6a75956f8f2b955e208599b77d8_414645_1100x0_resize_q75_box.jpg 1100w , /blog/how-to-stay-hot/crystals_hue94aa6a75956f8f2b955e208599b77d8_414645_1400x0_resize_q75_box.jpg 1400w , /blog/how-to-stay-hot/crystals_hue94aa6a75956f8f2b955e208599b77d8_414645_1800x0_resize_q75_box.jpg 1800w ' src="https://briankoberlein.com/blog/how-to-stay-hot/crystals_hue94aa6a75956f8f2b955e208599b77d8_414645_300x0_resize_q75_box.jpg" loading="lazy" width="1920" height="1440" alt="Artist illustration of crystals forming within a white dwarf."/> <span class="attribution">University of Warwick/Mark Garlick</span></span> </a> <figcaption>Artist illustration of crystals forming within a white dwarf.</figcaption> </figure> <p>At the end of their lives, most stars including the Sun will become white dwarfs. After a red dwarf or sun-like star consumes all the hydrogen and helium it can, the remains of the star will collapse under its own weight, shrinking ever more until the quantum pressure of electrons becomes strong enough to counter gravity. White dwarfs begin their days as brilliantly hot embers of degenerate matter and grow ever cooler and dimmer as they age.</p> <p>Because a white dwarf doesn&rsquo;t produce new energy through nuclear fusion, it has only remnant thermal energy to keep it warm. This fact allows astronomers to determine the age of a white dwarf by its temperature. Basically, the cooler a white dwarf is, the older it is. But there seem to be some exceptions. Astronomers have other ways to estimate the age of a white dwarf, such as comparing it to the age of the cluster of stars it&rsquo;s in. They&rsquo;ve found that some white dwarfs are a bit hotter than they should be. A new study may help explain why.<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup></p> <figure class="left"> <a href="https://briankoberlein.com/blog/how-to-stay-hot/structure.png"> <span class="credit"> <img srcset=' /blog/how-to-stay-hot/structure_huabb3b1d1b2b0c8ba85a31b6e6f565b62_185817_300x0_resize_box_3.png 300w , /blog/how-to-stay-hot/structure_huabb3b1d1b2b0c8ba85a31b6e6f565b62_185817_350x0_resize_box_3.png 350w , /blog/how-to-stay-hot/structure_huabb3b1d1b2b0c8ba85a31b6e6f565b62_185817_550x0_resize_box_3.png 550w , /blog/how-to-stay-hot/structure_huabb3b1d1b2b0c8ba85a31b6e6f565b62_185817_600x0_resize_box_3.png 600w , /blog/how-to-stay-hot/structure_huabb3b1d1b2b0c8ba85a31b6e6f565b62_185817_700x0_resize_box_3.png 700w , /blog/how-to-stay-hot/structure_huabb3b1d1b2b0c8ba85a31b6e6f565b62_185817_1100x0_resize_box_3.png 1100w ' src="https://briankoberlein.com/blog/how-to-stay-hot/structure_huabb3b1d1b2b0c8ba85a31b6e6f565b62_185817_300x0_resize_box_3.png" loading="lazy" width="2844" height="1855" alt="Schematic representation of the two scenarios of white dwarf crystallization."/> <span class="attribution">Sihao Cheng and Simon Blouin</span></span> </a> <figcaption>Schematic representation of the two scenarios of white dwarf crystallization.</figcaption> </figure> <p>It has to do with the way the interior of a white dwarf cools over time. In its early days, a white dwarf has an exterior solid crust with a fluid interior, similar to the structure of a planet such as Earth. The interior is a hot fluid of degenerate matter, but as it cools it can crystalize. It&rsquo;s generally been thought that crystalization initiates at the core where pressure is greatest, and then expands outward as the star cools. This means that white dwarfs experience a fast initial cooling, then a crystalization period where the surface temperature is fairly constant, and finally a final cooling period after core crystalization is over.</p> <p>This new study shows how crystalization can occur in a different way. Rather than bulk crystalization, small crystals can form within the warm interior. Just as ice crystals are less dense than the surrounding water, so are these initial crystals of white dwarf matter. And like ice particles, these crystals float upward from the core. As a result, the crystals form an insulating layer around the still-hot core. In this model, white dwarfs don&rsquo;t cool as much initially, and they stay warmer longer. This means that some white dwarfs can appear much warmer and younger than they actually are, so astronomers can&rsquo;t simply use temperature as an age measure for all white dwarfs.</p> <p>It isn&rsquo;t entirely clear why some white dwarfs crystalize from the core outward and why some form a crystal layer, but it is likely due to differences in composition. One clue comes from the fact that most white dwarfs form from a single old star, while other white dwarfs are formed during stellar mergers. The merger of white dwarfs could have a more diverse composition that encourages the formation of a crystal layer.</p> <div class="footnotes" role="doc-endnotes"> <hr> <ol> <li id="fn:1"> <p>Bédard, Antoine, et al. &ldquo;Buoyant crystals halt the cooling of white dwarf stars.&rdquo; <em>Nature</em> (2024).&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> </ol> </div>Clearing the Roomhttps://briankoberlein.com/blog/clearing-the-room/Wed, 06 Mar 2024 12:08:22 +0000https://briankoberlein.com/blog/clearing-the-room/ <figure class=""> <a href="https://briankoberlein.com/blog/clearing-the-room/eso1327a.jpg"> <span class="credit"> <img srcset=' /blog/clearing-the-room/eso1327a_hu7aeb1891fea9a4d69754212827d69323_2242731_300x0_resize_q75_box.jpg 300w , /blog/clearing-the-room/eso1327a_hu7aeb1891fea9a4d69754212827d69323_2242731_550x0_resize_q75_box.jpg 550w , /blog/clearing-the-room/eso1327a_hu7aeb1891fea9a4d69754212827d69323_2242731_700x0_resize_q75_box.jpg 700w , /blog/clearing-the-room/eso1327a_hu7aeb1891fea9a4d69754212827d69323_2242731_900x0_resize_q75_box.jpg 900w , /blog/clearing-the-room/eso1327a_hu7aeb1891fea9a4d69754212827d69323_2242731_1100x0_resize_q75_box.jpg 1100w , /blog/clearing-the-room/eso1327a_hu7aeb1891fea9a4d69754212827d69323_2242731_1400x0_resize_q75_box.jpg 1400w , /blog/clearing-the-room/eso1327a_hu7aeb1891fea9a4d69754212827d69323_2242731_1800x0_resize_q75_box.jpg 1800w ' src="https://briankoberlein.com/blog/clearing-the-room/eso1327a_hu7aeb1891fea9a4d69754212827d69323_2242731_300x0_resize_q75_box.jpg" loading="lazy" width="4000" height="2700" alt="An artistic impression adapted to highlight gas dispersing from a planet-forming disk."/> <span class="attribution">ESO/M. Kornmesser</span></span> </a> <figcaption>An artistic impression adapted to highlight gas dispersing from a planet-forming disk.</figcaption> </figure> <p>Nearly 5 billion years ago a region of gas gravitationally collapsed within a vast molecular cloud. At the center of the region, the Sun began to form, while around it formed a protoplanetary disk of gas and dust out of which Earth and the other planets of the solar system would form. We know this is how the solar system began because we have observed this process in systems throughout the galaxy. But there are details of the process we still don&rsquo;t understand, such as why gas planets are relatively rare in our system.</p> <p>Our solar system only has four gas planets. The rest are the rocky worlds of the inner solar system. Then there are countless asteroids and the icy worlds of Pluto and the outer solar system. Most of them don&rsquo;t contain a lot of volatile gasses, which is strange because early protoplanetary disks typically have a hundred times more gas than dust. So how does a gassy disk evolve into a planetary system of mostly rock? The answer can be found in recent observations of a young system known as TCha.<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup></p> <figure class="center"> <a href="https://briankoberlein.com/blog/clearing-the-room/winds.jpg"> <span class="credit"> <img srcset=' /blog/clearing-the-room/winds_hu6e2c368f2295abbe9c48dd068ca7e26b_375363_550x0_resize_q75_box.jpg 550w , /blog/clearing-the-room/winds_hu6e2c368f2295abbe9c48dd068ca7e26b_375363_700x0_resize_q75_box.jpg 700w , /blog/clearing-the-room/winds_hu6e2c368f2295abbe9c48dd068ca7e26b_375363_1100x0_resize_q75_box.jpg 1100w , /blog/clearing-the-room/winds_hu6e2c368f2295abbe9c48dd068ca7e26b_375363_1400x0_resize_q75_box.jpg 1400w ' src="https://briankoberlein.com/blog/clearing-the-room/winds_hu6e2c368f2295abbe9c48dd068ca7e26b_375363_300x0_resize_q75_box.jpg" loading="lazy" width="1499" height="863" alt="How photon pressure can clear a planetary system of gas."/> <span class="attribution">Naman S. Bajaj, et al</span></span> </a> <figcaption>How photon pressure can clear a planetary system of gas.</figcaption> </figure> <p>The general idea is that during the later stage of planetary formation the central star increases in brightness. The light from the star then drives winds within the disk which clears any remaining gas from the system. While this model can explain the type of planetary systems we observe, the process hasn&rsquo;t been observed directly. That is, until this recent study.</p> <p>TCha is a system in the late stages of planetary formation. Earlier observations found it has a large dust gap within the disk with a radius of more than 30 AU, indicating that much of the early material has already cleared. So in this new study, the team used observations from the James Webb Space Telescope (JWST) to measure the spectral lines of ionized argon and neon. This study is the first observation of a particular argon line, Ar III.</p> <p>The team made two main discoveries. The first is based on the ionizing energy levels, which indicates that argon is mostly ionized by extreme ultraviolet light, while neon is mostly ionized by X-rays. The second is that both gases are rapidly expanding away from the star, as seen by the Doppler shift of the spectral lines. Together these discoveries show that the gases are part of a stellar wind driven by high-energy photons.</p> <p>Based on the observations, the team estimates that the TCha disk is losing about a Moon&rsquo;s worth of mass every year, which is fast enough to clear the planetary disks in agreement with observations of planetary systems. While there are many details of planetary evolution we still don&rsquo;t understand, this study supports the standard model.</p> <div class="footnotes" role="doc-endnotes"> <hr> <ol> <li id="fn:1"> <p>Naman S. Bajaj, et al. &ldquo;JWST MIRI MRS Observations of T Cha: Discovery of a Spatially Resolved Disk Wind.&rdquo; <em>The Astronomical Journal</em> 167 (2024): 127.&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> </ol> </div>Scars Upon Starshttps://briankoberlein.com/blog/scars-upon-stars/Mon, 04 Mar 2024 11:49:12 +0000https://briankoberlein.com/blog/scars-upon-stars/ <figure class=""> <a href="https://briankoberlein.com/blog/scars-upon-stars/eso2403a.jpg"> <span class="credit"> <img srcset=' /blog/scars-upon-stars/eso2403a_hu3a74711af7615e084746f488ab1b8272_2552068_300x0_resize_q75_box.jpg 300w , /blog/scars-upon-stars/eso2403a_hu3a74711af7615e084746f488ab1b8272_2552068_550x0_resize_q75_box.jpg 550w , /blog/scars-upon-stars/eso2403a_hu3a74711af7615e084746f488ab1b8272_2552068_700x0_resize_q75_box.jpg 700w , /blog/scars-upon-stars/eso2403a_hu3a74711af7615e084746f488ab1b8272_2552068_900x0_resize_q75_box.jpg 900w , /blog/scars-upon-stars/eso2403a_hu3a74711af7615e084746f488ab1b8272_2552068_1100x0_resize_q75_box.jpg 1100w , /blog/scars-upon-stars/eso2403a_hu3a74711af7615e084746f488ab1b8272_2552068_1400x0_resize_q75_box.jpg 1400w , /blog/scars-upon-stars/eso2403a_hu3a74711af7615e084746f488ab1b8272_2552068_1800x0_resize_q75_box.jpg 1800w ' src="https://briankoberlein.com/blog/scars-upon-stars/eso2403a_hu3a74711af7615e084746f488ab1b8272_2552068_300x0_resize_q75_box.jpg" loading="lazy" width="5000" height="3437" alt="This artist’s impression shows the magnetic white dwarf WD 0816-310."/> <span class="attribution">ESO/L. Calçada</span></span> </a> <figcaption>This artist’s impression shows the magnetic white dwarf WD 0816-310.</figcaption> </figure> <p>Nothing is immortal. Everything has a finite existence, including the stars themselves. How a star dies depends on several factors, <a href="https://briankoberlein.com/blog/end-is-nigh/">most importantly their mass.</a> For the Sun, this means that in several billion years it will swell to a red giant as it churns through the last of its nuclear fuel. The core that remains will then collapse to become a white dwarf. Of course, the Sun is home to several planets, including Earth. What of their fate? What of ours? According to a recent study, the Sun&rsquo;s death might consume Earth in the end.<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup></p> <p>There are three main ideas as to how planetary systems end. One is that planets can be cast off into interstellar space to become <a href="https://briankoberlein.com/post/going-rogue/">rogue planets.</a> As a star loses its outer layers, its decreased gravitational pull may allow planets to escape their orbit. Another possibility is that planets can survive the red giant stage of a star and remain in orbit. We have <a href="https://briankoberlein.com/blog/sun-hot-world/">found several planets orbiting white dwarfs,</a> so we know this is a possibility. The third option is that during the red giant stage a planet is dragged down by stellar gas, spiraling ever inward until it collides with its star and is consumed. It&rsquo;s this option that is the focus of the new study.</p> <p>The study is based upon a white dwarf known as WD 0816-310, which is what&rsquo;s known as a &ldquo;polluted&rdquo; white dwarf. This means its spectrum shows the presence of metallic elements that aren&rsquo;t the product of the white dwarf itself. These contaminants could be caused by dust backfalling onto the white dwarf at the end of the red giant stage, or by asteroids or planets colliding with the star. Since heavier elements would tend to sink into the white dwarf and not be visible in the atmospheric spectra, the presence of these metals gives astronomers a way to study the time since accretion and look at whether it happened gradually or all at once.</p> <p>In this study, the team found evidence of metallic accretion in a short geological period. What&rsquo;s more, they found that the presence of metals was not evenly distributed across the star as you would expect from dust or a scattering of small asteroids. Instead, they found a localized region of metals, as a kind of metallic scar caused by a single impact. Based on their study, the team estimated that the impact was caused by an object at least as big as Vesta, which is the second largest asteroid in the solar system, with a diameter of about 500 km.</p> <p>Given the diversity of exoplanetary systems, it is likely that all three scenarios can occur. We know of rogue planets, we see dead stars with exoplanets, and now we see the scars of planetary impacts upon a white dwarf. One of these fates will be Earth&rsquo;s. For now, only time knows which outcome it will be.</p> <div class="footnotes" role="doc-endnotes"> <hr> <ol> <li id="fn:1"> <p>Bagnulo, Stefano, et al. &ldquo;Discovery of magnetically guided metal accretion onto a polluted white dwarf.&rdquo; <em>The Astrophysical Journal Letters</em> 963.1 (2024): L22.&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> </ol> </div>For Dust Thou Arthttps://briankoberlein.com/blog/for-dust-thou-art/Sat, 24 Feb 2024 08:33:49 +0000https://briankoberlein.com/blog/for-dust-thou-art/ <figure class=""> <a href="https://briankoberlein.com/blog/for-dust-thou-art/eso1421a.jpg"> <span class="credit"> <img srcset=' /blog/for-dust-thou-art/eso1421a_huafe51f6d61d58e1a82f42bf39cb2c039_2685607_300x0_resize_q75_box.jpg 300w , /blog/for-dust-thou-art/eso1421a_huafe51f6d61d58e1a82f42bf39cb2c039_2685607_550x0_resize_q75_box.jpg 550w , /blog/for-dust-thou-art/eso1421a_huafe51f6d61d58e1a82f42bf39cb2c039_2685607_700x0_resize_q75_box.jpg 700w , /blog/for-dust-thou-art/eso1421a_huafe51f6d61d58e1a82f42bf39cb2c039_2685607_900x0_resize_q75_box.jpg 900w , /blog/for-dust-thou-art/eso1421a_huafe51f6d61d58e1a82f42bf39cb2c039_2685607_1100x0_resize_q75_box.jpg 1100w , /blog/for-dust-thou-art/eso1421a_huafe51f6d61d58e1a82f42bf39cb2c039_2685607_1400x0_resize_q75_box.jpg 1400w , /blog/for-dust-thou-art/eso1421a_huafe51f6d61d58e1a82f42bf39cb2c039_2685607_1800x0_resize_q75_box.jpg 1800w ' src="https://briankoberlein.com/blog/for-dust-thou-art/eso1421a_huafe51f6d61d58e1a82f42bf39cb2c039_2685607_300x0_resize_q75_box.jpg" loading="lazy" width="3840" height="2400" alt="This artist’s impression shows dust forming in the environment around a supernova explosion."/> <span class="attribution">ESO/M. Kornmesser</span></span> </a> <figcaption>This artist’s impression shows dust forming in the environment around a supernova explosion.</figcaption> </figure> <p>Life on our planet appeared early in Earth&rsquo;s history. Surprisingly early, since in its early youth our planet didn&rsquo;t have much of the chemical ingredients necessary for life to evolve. Since prebiotic chemicals such as sugars and amino acids are known to appear in asteroids and comets, one idea is that Earth was seeded with the building blocks of life by early cometary and asteroid impacts. While this likely played a role, a new study shows that cosmic dust also seeded young Earth, and it may have made all the difference.<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup></p> <figure class="right"> <a href="https://briankoberlein.com/blog/for-dust-thou-art/dust.jpg"> <span class="credit"> <img srcset=' /blog/for-dust-thou-art/dust_hu169cc1e260f72185285bbc2c34e15919_354966_300x0_resize_q75_box.jpg 300w , /blog/for-dust-thou-art/dust_hu169cc1e260f72185285bbc2c34e15919_354966_350x0_resize_q75_box.jpg 350w , /blog/for-dust-thou-art/dust_hu169cc1e260f72185285bbc2c34e15919_354966_550x0_resize_q75_box.jpg 550w , /blog/for-dust-thou-art/dust_hu169cc1e260f72185285bbc2c34e15919_354966_600x0_resize_q75_box.jpg 600w , /blog/for-dust-thou-art/dust_hu169cc1e260f72185285bbc2c34e15919_354966_700x0_resize_q75_box.jpg 700w , /blog/for-dust-thou-art/dust_hu169cc1e260f72185285bbc2c34e15919_354966_1100x0_resize_q75_box.jpg 1100w ' src="https://briankoberlein.com/blog/for-dust-thou-art/dust_hu169cc1e260f72185285bbc2c34e15919_354966_300x0_resize_q75_box.jpg" loading="lazy" width="1500" height="1712" alt="How cosmic dust may have seeded Earth."/> <span class="attribution">Walton, et al</span></span> </a> <figcaption>How cosmic dust may have seeded Earth.</figcaption> </figure> <p>Although we&rsquo;ve long known that cosmic dust accumulated on early Earth, it&rsquo;s not been seen as a major source for early life because of how it accumulates. With comet and asteroid impacts, a great deal of prebiotic material is present at the site of the impact. Dust, on the other hand, is scattered across Earth&rsquo;s surface rather than accumulating locally. However, the authors of this new work noted that cosmic dust can accumulate and be concentrated in sedimentary deposits, and wanted to see how that might play a role in the early appearance of terrestrial life.</p> <p>Using estimates of the rate of cosmic dust accumulation in the early period of Earth and computer simulations of how that dust could accumulate in sediment layers over time, the team looked at how concentrated deposits might form. One of the things they noticed was that while cometary impacts could create a local spike in prebiotic material, the amount deposited by cosmic dust was much higher. They also found that the melting and freezing of glacial areas could significantly increase the concentration of chemicals from the dust. For example, for early sub-glacial lakes, the concentration of prebiotic chemistry from dust would have been much higher than that found at impact sites. This means that cosmic dust could have played a much larger role in the appearance of life than impacts.</p> <p>There is still much we have to learn about early life on Earth and how life can form from prebiotic chemistry, but it is clear that life on Earth is only possible because of extraterrestrial chemistry. From dust came the building blocks of life, and so we and every living thing on Earth can trace its lineage back to the early chemistry of dust in the solar system.</p> <div class="footnotes" role="doc-endnotes"> <hr> <ol> <li id="fn:1"> <p>Walton, Craig R., et al. &ldquo;Cosmic dust fertilization of glacial prebiotic chemistry on early Earth.&rdquo; <em>Nature Astronomy</em> (2024): 1-11.&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> </ol> </div>Galaxy Expresshttps://briankoberlein.com/blog/galaxy-express/Thu, 22 Feb 2024 12:28:14 +0000https://briankoberlein.com/blog/galaxy-express/ <figure class=""> <a href="https://briankoberlein.com/blog/galaxy-express/alma.jpg"> <span class="credit"> <img srcset=' /blog/galaxy-express/alma_hu26bfa006abf03d2b7ba61ca00f5031c7_1001600_300x0_resize_q75_box.jpg 300w , /blog/galaxy-express/alma_hu26bfa006abf03d2b7ba61ca00f5031c7_1001600_550x0_resize_q75_box.jpg 550w , /blog/galaxy-express/alma_hu26bfa006abf03d2b7ba61ca00f5031c7_1001600_700x0_resize_q75_box.jpg 700w , /blog/galaxy-express/alma_hu26bfa006abf03d2b7ba61ca00f5031c7_1001600_900x0_resize_q75_box.jpg 900w , /blog/galaxy-express/alma_hu26bfa006abf03d2b7ba61ca00f5031c7_1001600_1100x0_resize_q75_box.jpg 1100w , /blog/galaxy-express/alma_hu26bfa006abf03d2b7ba61ca00f5031c7_1001600_1400x0_resize_q75_box.jpg 1400w , /blog/galaxy-express/alma_hu26bfa006abf03d2b7ba61ca00f5031c7_1001600_1800x0_resize_q75_box.jpg 1800w ' src="https://briankoberlein.com/blog/galaxy-express/alma_hu26bfa006abf03d2b7ba61ca00f5031c7_1001600_300x0_resize_q75_box.jpg" loading="lazy" width="1920" height="1280" alt="The Atacama Large Millimeter/submillimeter Array (ALMA)."/> <span class="attribution">C. Padilla, NRAO/AUI/NSF</span></span> </a> <figcaption>The Atacama Large Millimeter/submillimeter Array (ALMA).</figcaption> </figure> <p>The conditions for life throughout the Universe are so plentiful that it seems reasonable to presume there must be extra-terrestrial civilizations in the galaxy. But if that&rsquo;s true, where are they? The Search for Extra-terrestrial Intelligence (SETI) program and others have long sought to find signals from these civilizations, but so far there has been nothing conclusive. Part of the challenge is that we don&rsquo;t know what the nature of an alien signal might be. It&rsquo;s a bit like finding a needle in a haystack when you don&rsquo;t know what the needle looks like. Fortunately, any alien civilization would still be bound by the same physical laws we are, and we can use that to consider what might be possible. One way to better our odds of finding something would be to focus not on a direct signal from a single world, but the broader echos of an interstellar network of signals.<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup></p> <p>As noted in a 2022 paper on the <em>arXiv</em>, one physical constraint is that there is a great deal of dust and interstellar gas in the Milky Way. Since radio light penetrates gas and dust better than visible light, the signals sent between stars are likely to be <a href="https://briankoberlein.com/blog/et-phone-home/">microwave radio signals.</a> Another fact is that if you are traveling between the stars you need to know where you are and where you are going. One way to do this is to use <a href="https://briankoberlein.com/post/you-are-here/">pulsars as navigational beacons.</a> In the paper the author argues that these can be combined as a broadband radio signal from the hub of the alien civilization that contains x-ray pulsar navigation metadata (XNAV).</p> <figure class="right"> <a href="https://briankoberlein.com/blog/galaxy-express/network.jpg"> <span class="credit"> <img srcset=' /blog/galaxy-express/network_huf01f926e28ad76c8c1951a24e8e736f2_169655_300x0_resize_q75_box.jpg 300w , /blog/galaxy-express/network_huf01f926e28ad76c8c1951a24e8e736f2_169655_350x0_resize_q75_box.jpg 350w , /blog/galaxy-express/network_huf01f926e28ad76c8c1951a24e8e736f2_169655_550x0_resize_q75_box.jpg 550w , /blog/galaxy-express/network_huf01f926e28ad76c8c1951a24e8e736f2_169655_600x0_resize_q75_box.jpg 600w , /blog/galaxy-express/network_huf01f926e28ad76c8c1951a24e8e736f2_169655_700x0_resize_q75_box.jpg 700w , /blog/galaxy-express/network_huf01f926e28ad76c8c1951a24e8e736f2_169655_1100x0_resize_q75_box.jpg 1100w ' src="https://briankoberlein.com/blog/galaxy-express/network_huf01f926e28ad76c8c1951a24e8e736f2_169655_300x0_resize_q75_box.jpg" loading="lazy" width="1384" height="1412" alt="A 3-pulsar navigation system for an ET civilization."/> <span class="attribution">Ross Davis (2022)</span></span> </a> <figcaption>A 3-pulsar navigation system for an ET civilization.</figcaption> </figure> <p>One of the biggest challenges of detecting stray alien signals is that they would likely be difficult to distinguish from random noise. Even simple signals such as television broadcasts rely upon a known protocol. Without that protocol, we can&rsquo;t decipher the message. This is similar to the challenge of breaking the Enigma code during World War II. One of the breakthroughs came when it was realized that most messages contained a weather report, so the message likely contained the German word for weather. Metadata in an alien signal could serve a similar role. If we know radio signals should contain XNAV metadata, then we can use this as a starting point. In game theory this is known as a Shelling Point.</p> <p>The author outlines nine steps for how an interstellar civilization might construct a pulsar navigation system, and what the pattern of that network might be. By creating multiple scenarios, we might be able to recognize certain patterns as technosignatures. As the author notes, one limitation of this approach is that any metadata scenario we imagine is still based on how homo sapiens think, which might not be how an alien intelligence sees things.</p> <p>All of this is speculative, but it&rsquo;s worth considering. We will only recognize an alien signal if we better understand the forms they might take, and perhaps a few wild ideas like this one are exactly what we need.</p> <div class="footnotes" role="doc-endnotes"> <hr> <ol> <li id="fn:1"> <p>Davis, Ross. &ldquo;Finding the ET Signal from the Cosmic Noise.&rdquo; <em>arXiv preprint</em> arXiv:2204.04405 (2022).&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> </ol> </div>Beast Starshttps://briankoberlein.com/blog/beast-stars/Mon, 19 Feb 2024 10:55:00 +0000https://briankoberlein.com/blog/beast-stars/<p>One of the central predictions of general relativity is that in the end, gravity wins. Stars will fuse hydrogen into new elements to fight gravity and can oppose it for a time. Electrons and neutrons exert pressure to counter gravity, but their stability against that constant pull limits the amount of mass a white dwarf or neutron star can have. All of this can be countered by gathering more mass together. Beyond about 3 solar masses, give or take, gravity will overpower all other forces and collapse the mass into a black hole.</p> <p>While black holes have a great deal of theoretical and observational evidence to prove their existence, the theory of black holes is not without issue. For one, general relativity predicts that the mass compresses to an <a href="https://briankoberlein.com/blog/pointed-debate/">infinitely dense singularity where the laws of physics break down.</a> This singularity is shrouded by an <a href="https://briankoberlein.com/blog/on-the-edge/">event horizon,</a> which serves as a point of no return for anything devoured by the black hole. Both of these are problematic, so there has been a long history of trying to find some alternative. Some mechanism that prevents singularities and event horizons from forming.</p> <p>One alternative is a gravitational vacuum star or gravitational condensate star, commonly called a gravastar. It was first proposed in 2001, and takes advantage of the fact that most of the energy in the universe is not regular matter or even dark matter, but dark energy. Dark energy drives cosmic expansion, so perhaps it could oppose gravitational collapse in high densities.</p> <figure class="left"> <a href="https://briankoberlein.com/blog/beast-stars/gravastar.jpg"> <span class="credit"> <img srcset=' /blog/beast-stars/gravastar_hu35c543b71b53530d7075e5ea11ab8b2f_143962_300x0_resize_q75_box.jpg 300w , /blog/beast-stars/gravastar_hu35c543b71b53530d7075e5ea11ab8b2f_143962_350x0_resize_q75_box.jpg 350w , /blog/beast-stars/gravastar_hu35c543b71b53530d7075e5ea11ab8b2f_143962_550x0_resize_q75_box.jpg 550w , /blog/beast-stars/gravastar_hu35c543b71b53530d7075e5ea11ab8b2f_143962_600x0_resize_q75_box.jpg 600w ' src="https://briankoberlein.com/blog/beast-stars/gravastar_hu35c543b71b53530d7075e5ea11ab8b2f_143962_300x0_resize_q75_box.jpg" loading="lazy" width="650" height="650" alt="Illustration of a hypothetical gravastar."/> <span class="attribution">Daniel Jampolski and Luciano Rezzolla, Goethe University Frankfurt</span></span> </a> <figcaption>Illustration of a hypothetical gravastar.</figcaption> </figure> <p>The original gravastar model proposed a kind of Bose-Einstein condensate of dark energy surrounded by a thin shell of regular matter. The internal condensate ensures that the gravastar has no singularity, while the dense shell of matter ensures that the gravastar appears similar to a black hole from the outside. Interesting idea, but there are two central problems. One is that the shell is unstable, particularly if the gravastar is rotating. There are ways to tweak things just so to make it stable, but such ideal conditions aren&rsquo;t likely to occur in nature. The second problem is that gravitational wave observations of large body mergers confirm the standard black hole model. But a new gravastar model might solve some of those problems.<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup></p> <p>The new model essentially nests multiple gravastars together, somewhat like those nested Matryoshka dolls. Rather than a single shell enclosing exotic dark energy, the model has a layers of nested shells with dark energy between the layers. The authors refer to this model as a nestar, or nested gravastar. This alternative model makes the gravastar more stable, since the tension of dark energy is better balanced by the weight of the shells. The interior structure of the nestar also means that the gravitational waves of a nestar and black hole are more similar, meaning that technically their existence can&rsquo;t be ruled out.</p> <p>That said, even the authors note that there is no likely scenario that could produce nestars. They likely don&rsquo;t exist, and it&rsquo;s almost certain that what we observe as black holes are true black holes. But studies such as this one are great for testing the limits of general relativity. They help us understand what is possible within the framework of the theory, which in turn helps us better understand gravitational physics.</p> <div class="footnotes" role="doc-endnotes"> <hr> <ol> <li id="fn:1"> <p>Jampolski, Daniel and Rezzolla, Luciano. &ldquo;Nested solutions of gravitational condensate stars.&rdquo; <em>Classical and Quantum Gravity</em> 41 (2024): 065014.&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> </ol> </div>The Outer Worldshttps://briankoberlein.com/blog/outer-worlds/Sat, 17 Feb 2024 09:20:32 +0000https://briankoberlein.com/blog/outer-worlds/ <figure class=""> <a href="https://briankoberlein.com/blog/outer-worlds/worlds.jpg"> <span class="credit"> <img srcset=' /blog/outer-worlds/worlds_hua39fd26bc4073495983718e61ea7e272_4664933_300x0_resize_q75_box.jpg 300w , /blog/outer-worlds/worlds_hua39fd26bc4073495983718e61ea7e272_4664933_550x0_resize_q75_box.jpg 550w , /blog/outer-worlds/worlds_hua39fd26bc4073495983718e61ea7e272_4664933_700x0_resize_q75_box.jpg 700w , /blog/outer-worlds/worlds_hua39fd26bc4073495983718e61ea7e272_4664933_900x0_resize_q75_box.jpg 900w , /blog/outer-worlds/worlds_hua39fd26bc4073495983718e61ea7e272_4664933_1100x0_resize_q75_box.jpg 1100w , /blog/outer-worlds/worlds_hua39fd26bc4073495983718e61ea7e272_4664933_1400x0_resize_q75_box.jpg 1400w , /blog/outer-worlds/worlds_hua39fd26bc4073495983718e61ea7e272_4664933_1800x0_resize_q75_box.jpg 1800w ' src="https://briankoberlein.com/blog/outer-worlds/worlds_hua39fd26bc4073495983718e61ea7e272_4664933_300x0_resize_q75_box.jpg" loading="lazy" width="5740" height="4000" alt="Illustration of the icy dwarf planets Eris and Makemake."/> <span class="attribution">Southwest Research Institute</span></span> </a> <figcaption>Illustration of the icy dwarf planets Eris and Makemake.</figcaption> </figure> <p>Whether or not you agree that Pluto isn&rsquo;t a planet, in many ways, Pluto is quite different from the classical planets. It&rsquo;s smaller than the Moon, has an elliptical orbit that brings it closer to the Sun than Neptune at times, and is part of a collection of icy bodies on the edge of our solar system. It was also thought to be a cold dead world until the flyby of New Horizons proved otherwise. The plucky little spacecraft showed us that Pluto was geologically active, with a <a href="https://briankoberlein.com/blog/waiting-to-be-seen/">thin atmosphere and mountains that rise above icy plains.</a> Geologically, Pluto is more similar to Earth than the Moon, a fact that has led some to reconsider Pluto&rsquo;s designation as a dwarf planet.</p> <p>Astronomers still aren&rsquo;t sure how Pluto has remained geologically active. Perhaps the gravitational interactions with its moon Charon, or perhaps interior radioactive decay. But regardless of the cause, the general thought has been that Pluto is an exception, not a rule. Other outer worlds of similar size and composition are likely dead worlds. But a new study shows that isn&rsquo;t the case for at least two dwarf planets, Eris and Makemake.<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup></p> <figure class="center"> <a href="https://briankoberlein.com/blog/outer-worlds/telescope.jpg"> <span class="credit"> <img srcset=' /blog/outer-worlds/telescope_hu7ddfaef20a85e8a089da431a1136a2d3_375527_550x0_resize_q75_box.jpg 550w , /blog/outer-worlds/telescope_hu7ddfaef20a85e8a089da431a1136a2d3_375527_700x0_resize_q75_box.jpg 700w , /blog/outer-worlds/telescope_hu7ddfaef20a85e8a089da431a1136a2d3_375527_1100x0_resize_q75_box.jpg 1100w , /blog/outer-worlds/telescope_hu7ddfaef20a85e8a089da431a1136a2d3_375527_1400x0_resize_q75_box.jpg 1400w ' src="https://briankoberlein.com/blog/outer-worlds/telescope_hu7ddfaef20a85e8a089da431a1136a2d3_375527_300x0_resize_q75_box.jpg" loading="lazy" width="1600" height="800" alt="Telescopic images of Makemake (left) and Eris (right)."/> <span class="attribution">NASA/ESA</span></span> </a> <figcaption>Telescopic images of Makemake (left) and Eris (right).</figcaption> </figure> <p>This new study doesn&rsquo;t rely on high-resolution images like we have for Pluto. Our current observations of Eris and Makemake show them only as small, blurry dots. But we do have spectral observations of these worlds, which is where this study comes in.</p> <p>The team looked at the spectral lines of molecules on the surface of these worlds, most specifically that of methane. Methane, or CH<sub>4</sub> has two important variants. One is composed of standard hydrogen atoms, while the other contains one or more atoms of a type of hydrogen known as deuterium. Deuterium has a nucleus containing a proton and neutron rather than just a proton, and this skews the spectrum of methane a bit. From the spectral observations, the team could measure the D/H ratio for methane on both worlds.</p> <figure class="right"> <a href="https://briankoberlein.com/blog/outer-worlds/ratios.jpg"> <span class="credit"> <img srcset=' /blog/outer-worlds/ratios_hucb647d286ef4deb70fe5bfe0b1c5f1c9_95261_300x0_resize_q75_box.jpg 300w , /blog/outer-worlds/ratios_hucb647d286ef4deb70fe5bfe0b1c5f1c9_95261_350x0_resize_q75_box.jpg 350w , /blog/outer-worlds/ratios_hucb647d286ef4deb70fe5bfe0b1c5f1c9_95261_550x0_resize_q75_box.jpg 550w , /blog/outer-worlds/ratios_hucb647d286ef4deb70fe5bfe0b1c5f1c9_95261_600x0_resize_q75_box.jpg 600w , /blog/outer-worlds/ratios_hucb647d286ef4deb70fe5bfe0b1c5f1c9_95261_700x0_resize_q75_box.jpg 700w , /blog/outer-worlds/ratios_hucb647d286ef4deb70fe5bfe0b1c5f1c9_95261_1100x0_resize_q75_box.jpg 1100w ' src="https://briankoberlein.com/blog/outer-worlds/ratios_hucb647d286ef4deb70fe5bfe0b1c5f1c9_95261_300x0_resize_q75_box.jpg" loading="lazy" width="1550" height="1108" alt="How D/H ratios compare to possible origins."/> <span class="attribution">Glein, et al</span></span> </a> <figcaption>How D/H ratios compare to possible origins.</figcaption> </figure> <p>This ratio is determined by the source of the methane. If Eris and Makemake are dead worlds, then the methane they have stems from their origin more than 4 billion years ago, and the D/H level should be on the higher end. On the other hand, if the surface methane was generated through an interior process and vented through active geological processes, then the D/H ratio should be lower. The team found that the ratio is most consistent with thermogenic and abiotic mechanisms, suggesting that both Eris and Makemake are active worlds, or at least were active in geologically recent times.</p> <p>Eris is about the same size as Pluto, so it isn&rsquo;t too surprising that it&rsquo;s a geologically active world given what we now know about Pluto. But Makemake is much smaller, about 60% the size of Pluto. If Makemake is an active world, then it is likely that other dwarf planets such as Haumea are as well. If that&rsquo;s the case, then most if not all dwarf planets are geologically active. As the authors suggest, it might be worth sending a probe or two to the outer worlds for more study.</p> <div class="footnotes" role="doc-endnotes"> <hr> <ol> <li id="fn:1"> <p>Glein, Christopher R., et al. &ldquo;Moderate D/H ratios in methane ice on Eris and Makemake as evidence of hydrothermal or metamorphic processes in their interiors: Geochemical analysis.&rdquo; <em>Icarus</em> (2024): 115999.&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> </ol> </div>To Map the Distant Heavenshttps://briankoberlein.com/blog/map-the-distant-heavens/Fri, 16 Feb 2024 10:51:54 +0000https://briankoberlein.com/blog/map-the-distant-heavens/ <figure class=""> <a href="https://briankoberlein.com/blog/map-the-distant-heavens/euclid.jpg"> <span class="credit"> <img srcset=' /blog/map-the-distant-heavens/euclid_hua39fd26bc4073495983718e61ea7e272_4645809_300x0_resize_q75_box.jpg 300w , /blog/map-the-distant-heavens/euclid_hua39fd26bc4073495983718e61ea7e272_4645809_550x0_resize_q75_box.jpg 550w , /blog/map-the-distant-heavens/euclid_hua39fd26bc4073495983718e61ea7e272_4645809_700x0_resize_q75_box.jpg 700w , /blog/map-the-distant-heavens/euclid_hua39fd26bc4073495983718e61ea7e272_4645809_900x0_resize_q75_box.jpg 900w , /blog/map-the-distant-heavens/euclid_hua39fd26bc4073495983718e61ea7e272_4645809_1100x0_resize_q75_box.jpg 1100w , /blog/map-the-distant-heavens/euclid_hua39fd26bc4073495983718e61ea7e272_4645809_1400x0_resize_q75_box.jpg 1400w , /blog/map-the-distant-heavens/euclid_hua39fd26bc4073495983718e61ea7e272_4645809_1800x0_resize_q75_box.jpg 1800w ' src="https://briankoberlein.com/blog/map-the-distant-heavens/euclid_hua39fd26bc4073495983718e61ea7e272_4645809_300x0_resize_q75_box.jpg" loading="lazy" width="4000" height="2250" alt="The areas that the space telescope Euclid will observe."/> <span class="attribution">ESA/Euclid/Euclid Consortium</span></span> </a> <figcaption>The areas that the space telescope Euclid will observe.</figcaption> </figure> <p>On July 1, 2023, the Euclid Spacecraft launched with a clear mission: to map the dark and distant Universe. To achieve that goal, over the next 6 years, Euclid will make 40,000 observations of the sky beyond the Milky Way. From this data astronomers will be able to map the positions of billions of galaxies, allowing astronomers to observe the effects of dark matter.</p> <p>There have been several galactic sky surveys before, but Euclid&rsquo;s mission will take them to the next level. Euclid is equipped with a widefield imaging system. With each 70-minute exposure of the dark sky, it will capture the image and spectra of more than 50,000 galaxies. When it is complete, the Euclid survey will be the most detailed survey of galactic positions and distances. The mission will also make several deep sky observations, where it focuses on the most distant and dim galaxies.</p> <figure class="right"> <a href="https://briankoberlein.com/blog/map-the-distant-heavens/view.jpg"> <span class="credit"> <img srcset=' /blog/map-the-distant-heavens/view_hua4ca8356e53b8e568b51c826cf9f4982_1477062_300x0_resize_q75_box.jpg 300w , /blog/map-the-distant-heavens/view_hua4ca8356e53b8e568b51c826cf9f4982_1477062_350x0_resize_q75_box.jpg 350w , /blog/map-the-distant-heavens/view_hua4ca8356e53b8e568b51c826cf9f4982_1477062_550x0_resize_q75_box.jpg 550w , /blog/map-the-distant-heavens/view_hua4ca8356e53b8e568b51c826cf9f4982_1477062_600x0_resize_q75_box.jpg 600w , /blog/map-the-distant-heavens/view_hua4ca8356e53b8e568b51c826cf9f4982_1477062_700x0_resize_q75_box.jpg 700w , /blog/map-the-distant-heavens/view_hua4ca8356e53b8e568b51c826cf9f4982_1477062_1100x0_resize_q75_box.jpg 1100w ' src="https://briankoberlein.com/blog/map-the-distant-heavens/view_hua4ca8356e53b8e568b51c826cf9f4982_1477062_300x0_resize_q75_box.jpg" loading="lazy" width="1920" height="2138" alt="Euclid&#39;s field of view compared to the Moon."/> <span class="attribution">ESA/ESA/Euclid/Euclid Consortium/NASA, S. Brunier</span></span> </a> <figcaption>Euclid&rsquo;s field of view compared to the Moon.</figcaption> </figure> <p>One of the mysteries Euclid could answer is the nature of dark energy. The standard model of cosmology describes dark energy as a property of space and time. A cosmological constant that drives cosmic expansion. But some theories of dark energy argue that <a href="https://briankoberlein.com/post/phantom-menace/">it&rsquo;s an energy field within space and time,</a> and that cosmic expansion isn&rsquo;t constant. Euclid will study whether cosmic expansion varies, allowing astronomers to constrain or rule out certain models. The mission will also look at how dark matter distorts galaxies, allowing us to learn more about the properties of dark matter and how it interacts with regular matter.</p> <p>The Euclid mission officially began its survey on Valentine&rsquo;s Day and will complete about 15% of its survey this year. An initial deep sky data set will be released in Spring 2025, and data from the first year of the general survey will be released in Summer 2026.</p> <p>You can read more about the <a href="https://www.esa.int/Science_Exploration/Space_Science/Euclid">Euclid Mission on ESA&rsquo;s website.</a></p>The Power of Magnetismhttps://briankoberlein.com/blog/power-of-magnetism/Thu, 15 Feb 2024 12:02:33 +0000https://briankoberlein.com/blog/power-of-magnetism/ <figure class=""> <a href="https://briankoberlein.com/blog/power-of-magnetism/pia26274.jpg"> <span class="credit"> <img srcset=' /blog/power-of-magnetism/pia26274_huc8a119e9d46d034ded550ff0030f5675_959644_300x0_resize_q75_box.jpg 300w , /blog/power-of-magnetism/pia26274_huc8a119e9d46d034ded550ff0030f5675_959644_550x0_resize_q75_box.jpg 550w , /blog/power-of-magnetism/pia26274_huc8a119e9d46d034ded550ff0030f5675_959644_700x0_resize_q75_box.jpg 700w , /blog/power-of-magnetism/pia26274_huc8a119e9d46d034ded550ff0030f5675_959644_900x0_resize_q75_box.jpg 900w , /blog/power-of-magnetism/pia26274_huc8a119e9d46d034ded550ff0030f5675_959644_1100x0_resize_q75_box.jpg 1100w , /blog/power-of-magnetism/pia26274_huc8a119e9d46d034ded550ff0030f5675_959644_1400x0_resize_q75_box.jpg 1400w , /blog/power-of-magnetism/pia26274_huc8a119e9d46d034ded550ff0030f5675_959644_1800x0_resize_q75_box.jpg 1800w ' src="https://briankoberlein.com/blog/power-of-magnetism/pia26274_huc8a119e9d46d034ded550ff0030f5675_959644_300x0_resize_q75_box.jpg" loading="lazy" width="4800" height="2700" alt="Artist&#39;s concept of a magnetar."/> <span class="attribution">NASA/JPL-Caltech</span></span> </a> <figcaption>Artist&rsquo;s concept of a magnetar.</figcaption> </figure> <p>Fast radio bursts (FRBs) are strange events. They can last only milliseconds, but during that time can outshine a galaxy. Some FRBs are repeaters, meaning that they can occur more than once from the same location, while others seem to occur just once. We still aren&rsquo;t entirely sure what causes them, or even if the two types have the same cause. But thanks to a collaboration of observations from ground-based radio telescopes and space-based X-ray observatories, we are starting to figure FRBs out.</p> <p>Most FRBs happen well beyond our galaxy, so while we can pin down their locations, it&rsquo;s difficult to observe any details about their cause. Then in 2020 we <a href="https://briankoberlein.com/blog/closer-to-home/">observed a fast radio burst in our galaxy.</a> Subsequent observations found that it originated in the region of a highly magnetized neutron star known as a magnetar. This led to the idea that magnetars were the source of FRBs, possibly through magnetic flares similar to solar flares. But magnetars and Sun-like stars are very different. It still wasn&rsquo;t clear how a magnetar could release such a tremendous amount of energy so quickly, even with their intense magnetic fields. Now a new study suggests the magnetar&rsquo;s rotation plays a key role.<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup></p> <figure class="left"> <a href="https://briankoberlein.com/blog/power-of-magnetism/glitch.jpg"> <span class="credit"> <img srcset=' /blog/power-of-magnetism/glitch_huf0ac67e68bdf52775e6b85dedd085172_195358_300x0_resize_q75_box.jpg 300w , /blog/power-of-magnetism/glitch_huf0ac67e68bdf52775e6b85dedd085172_195358_350x0_resize_q75_box.jpg 350w , /blog/power-of-magnetism/glitch_huf0ac67e68bdf52775e6b85dedd085172_195358_550x0_resize_q75_box.jpg 550w , /blog/power-of-magnetism/glitch_huf0ac67e68bdf52775e6b85dedd085172_195358_600x0_resize_q75_box.jpg 600w , /blog/power-of-magnetism/glitch_huf0ac67e68bdf52775e6b85dedd085172_195358_700x0_resize_q75_box.jpg 700w , /blog/power-of-magnetism/glitch_huf0ac67e68bdf52775e6b85dedd085172_195358_1100x0_resize_q75_box.jpg 1100w ' src="https://briankoberlein.com/blog/power-of-magnetism/glitch_huf0ac67e68bdf52775e6b85dedd085172_195358_300x0_resize_q75_box.jpg" loading="lazy" width="1496" height="1388" alt="How two magnetar glitches correlate with a fast radio burst."/> <span class="attribution">Hu, Chin-Ping, et al</span></span> </a> <figcaption>How two magnetar glitches correlate with a fast radio burst.</figcaption> </figure> <p>The study focuses on the 2020 FRB magnetar. Known as SGR 1935+2154, it is both a magnetar and a pulsar. This means it emits a regular radio pop as it rotates. Pulsars are incredibly regular and are used as a kind of cosmic clock for everything from <a href="https://briankoberlein.com/blog/matter-of-timing/">studying gravitational waves</a> to <a href="https://briankoberlein.com/post/you-are-here/">hypothetical navigation through the galaxy.</a> But over time a pulsar&rsquo;s rotation slows down as rotational energy radiates away thanks to its magnetic field. By observing this rate of decay, astronomers can better understand the structure of neutron stars and magnetars.</p> <p>But sometimes the rate of rotation will shift suddenly. It&rsquo;s known as a <a href="https://briankoberlein.com/post/glitch-and-antiglitch/">glitch if the rotation suddenly speeds up, and an anti-glitch if it suddenly slows down.</a> These glitches are thought to occur when there&rsquo;s some kind of sudden structural change in the neutron star, such as a starquake.</p> <p>In 2022, NASA&rsquo;s Nuclear Spectroscopic Telescope Array (NUSTAR) spacecraft and the Neutron Star Interior Composition Explorer (NICER) on the international space station both observed another fast radio burst from SGR 1935+2154. Together they had X-ray data on the magnetar before, during, and after the burst. The team then looked at radio observations during the same time and found a dip in the pulsar rotation rate during the burst. This implies a connection between rotation and burst.</p> <p>Overall what the team observed was a fluttering of X-ray emissions from SGR 1935+2154 a bit before the burst, then a glitch in the rotation, the burst itself, and a return to the regular rotation rate. This is only one observation, but it looks like the magnetar had the magnetic energy ready to release before the burst, and the shift in rotation created the conditions necessary to generate the FRB.</p> <div class="footnotes" role="doc-endnotes"> <hr> <ol> <li id="fn:1"> <p>Hu, Chin-Ping, et al. &ldquo;Rapid spin changes around a magnetar fast radio burst.&rdquo; <em>Nature</em> 626 (2024): 500-504.&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> </ol> </div>Change of Planshttps://briankoberlein.com/blog/change-of-plans/Wed, 14 Feb 2024 12:53:23 +0000https://briankoberlein.com/blog/change-of-plans/ <figure class=""> <a href="https://briankoberlein.com/blog/change-of-plans/ancientstar.jpg"> <span class="credit"> <img srcset=' /blog/change-of-plans/ancientstar_hud70bbd3e6408f5344f6bc771f660113f_367518_300x0_resize_q75_box.jpg 300w , /blog/change-of-plans/ancientstar_hud70bbd3e6408f5344f6bc771f660113f_367518_550x0_resize_q75_box.jpg 550w , /blog/change-of-plans/ancientstar_hud70bbd3e6408f5344f6bc771f660113f_367518_700x0_resize_q75_box.jpg 700w , /blog/change-of-plans/ancientstar_hud70bbd3e6408f5344f6bc771f660113f_367518_900x0_resize_q75_box.jpg 900w , /blog/change-of-plans/ancientstar_hud70bbd3e6408f5344f6bc771f660113f_367518_1100x0_resize_q75_box.jpg 1100w , /blog/change-of-plans/ancientstar_hud70bbd3e6408f5344f6bc771f660113f_367518_1400x0_resize_q75_box.jpg 1400w , /blog/change-of-plans/ancientstar_hud70bbd3e6408f5344f6bc771f660113f_367518_1800x0_resize_q75_box.jpg 1800w ' src="https://briankoberlein.com/blog/change-of-plans/ancientstar_hud70bbd3e6408f5344f6bc771f660113f_367518_300x0_resize_q75_box.jpg" loading="lazy" width="1995" height="1217" alt="Scholz’s Star seen from Earth 70,000 years ago."/> <span class="attribution">José A. Peñas/SINC</span></span> </a> <figcaption>Scholz’s Star seen from Earth 70,000 years ago.</figcaption> </figure> <p>The orbit of Earth around the Sun is always changing. It doesn&rsquo;t change significantly from year to year, but over time the gravitational tugs of the Moon and other planets cause Earth&rsquo;s orbit to vary. This migration affects Earth&rsquo;s climate. For example, the gradual shift of Earth&rsquo;s orbit and the changing tilt of Earth&rsquo;s axis leads to the <a href="https://briankoberlein.com/blog/man-for-all-seasons/">Milankovitch climate cycles.</a> So if you want to understand paleoclimate or the shift of Earth&rsquo;s climate across geologic time, it helps to know what Earth&rsquo;s orbit was in the distant past.</p> <p>Fortunately, Newtonian mechanics and the law of gravity work backward in time as well as forward. We can use Newtonian dynamics to predict eclipses and the trajectories of spacecraft to the outer solar system, but we can also use it to turn back the clock and map Earth&rsquo;s orbit into the deep past. Within limits.</p> <figure class="right"> <a href="https://briankoberlein.com/blog/change-of-plans/migration.jpg"> <span class="credit"> <img srcset=' /blog/change-of-plans/migration_hu9d9d028c352be9b2ce7860f4943eca06_87575_300x0_resize_q75_box.jpg 300w , /blog/change-of-plans/migration_hu9d9d028c352be9b2ce7860f4943eca06_87575_350x0_resize_q75_box.jpg 350w , /blog/change-of-plans/migration_hu9d9d028c352be9b2ce7860f4943eca06_87575_550x0_resize_q75_box.jpg 550w ' src="https://briankoberlein.com/blog/change-of-plans/migration_hu9d9d028c352be9b2ce7860f4943eca06_87575_300x0_resize_q75_box.jpg" loading="lazy" width="582" height="600" alt="The uncertainty of Earth&#39;s orbit 54 million years ago."/> <span class="attribution">N. Kaib/PSI</span></span> </a> <figcaption>The uncertainty of Earth&rsquo;s orbit 54 million years ago.</figcaption> </figure> <p>Since there is no exact solution for the orbital motion of more than two bodies, we have to run our calculations computationally. A bit of chaos comes into the works, so any uncertainty we have in the current positions and motions of large solar system bodies decreases the accuracy of our retrodiction the further back in time we go. Fortunately with radar ranging and other measurements, our computations are so accurate we can trace Earth&rsquo;s orbit back 100 million years into the past with some confidence. Or so we thought because a new paper demonstrates we&rsquo;ve been overlooking the gravitational effect of passing stars.<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup></p> <p>Most stars are too distant to have any measurable effect on Earth&rsquo;s orbit. They tug upon our world no more than the distant rocks of the Oort Cloud. But now and then a star will make a close approach. Not close enough to <a href="https://briankoberlein.com/post/close-encounters/">throw our solar system into chaos,</a> but close enough to give the solar planets a gravitational nudge. The most recent close approach was HD 7977. Right now the star is about 250 light-years away, but 2.8 million years ago it passed within 30,000 AU or half a light-year of the Sun. It may have passed as close as 4,000 AU from the Sun. At the larger distance, the gravitational effect of HD 7977 would be negligible, but at the closer end of the range, it would be significant. When you add this into the computational mix, the uncertainties of Earth&rsquo;s past orbit make it difficult to be confident more than 50 million years. And that has a significant impact on paleoclimate studies.</p> <p>For example, about 56 million years ago Earth entered a period known as the Paleocene-Eocene Thermal Maximum, where global temperatures rose 5 - 8 °C. Orbital models point to the fact that Earth&rsquo;s orbit was particularly eccentric during that time, which could be the underlying cause. But this new study raises the uncertainty of that conclusion, meaning that other factors such as geologic activity may have played a major role.</p> <p>It&rsquo;s estimated that a star passes within 10,000 AU of the Sun <a href="https://briankoberlein.com/blog/close-encounters/">every 20 million years or so.</a> This means that as we map Earth&rsquo;s orbital motion deeper into the past, we must also look for effects that may be written in the stars.</p> <div class="footnotes" role="doc-endnotes"> <hr> <ol> <li id="fn:1"> <p>Kaib, Nathan A. and Raymond, Sean N. &ldquo;Passing Stars as an Important Driver of Paleoclimate and the Solar System&rsquo;s Orbital Evolution.&rdquo; <em>Astrophysical Journal Letters</em> 962 (2024): L28.&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> </ol> </div>Fast and Farhttps://briankoberlein.com/blog/fast-and-far/Mon, 12 Feb 2024 11:02:37 +0000https://briankoberlein.com/blog/fast-and-far/ <figure class=""> <a href="https://briankoberlein.com/blog/fast-and-far/fast.jpg"> <span class="credit"> <img srcset=' /blog/fast-and-far/fast_hu7d20b49d54ed348cfdc418d803ccec3c_1123399_300x0_resize_q75_box.jpg 300w , /blog/fast-and-far/fast_hu7d20b49d54ed348cfdc418d803ccec3c_1123399_550x0_resize_q75_box.jpg 550w , /blog/fast-and-far/fast_hu7d20b49d54ed348cfdc418d803ccec3c_1123399_700x0_resize_q75_box.jpg 700w , /blog/fast-and-far/fast_hu7d20b49d54ed348cfdc418d803ccec3c_1123399_900x0_resize_q75_box.jpg 900w , /blog/fast-and-far/fast_hu7d20b49d54ed348cfdc418d803ccec3c_1123399_1100x0_resize_q75_box.jpg 1100w , /blog/fast-and-far/fast_hu7d20b49d54ed348cfdc418d803ccec3c_1123399_1400x0_resize_q75_box.jpg 1400w , /blog/fast-and-far/fast_hu7d20b49d54ed348cfdc418d803ccec3c_1123399_1800x0_resize_q75_box.jpg 1800w ' src="https://briankoberlein.com/blog/fast-and-far/fast_hu7d20b49d54ed348cfdc418d803ccec3c_1123399_300x0_resize_q75_box.jpg" loading="lazy" width="3695" height="2186" alt="FAST catches a real pulse from FRB 121102."/> <span class="attribution">NAOC</span></span> </a> <figcaption>FAST catches a real pulse from FRB 121102.</figcaption> </figure> <p>Now and then there is a bright radio flash somewhere in the sky. It can last anywhere from a few milliseconds to a few seconds. They appear somewhat at random, and we still aren&rsquo;t sure what they are. We call them <a href="https://briankoberlein.com/blog/distant-call/">fast radio bursts (FRBs).</a> Right now the leading theory is that they are caused by highly magnetic neutron stars known as magnetars. With observatories such as <a href="https://briankoberlein.com/blog/chime-in/">CHIME</a> we are now able to see lots of them, which could give astronomers a new way to measure the rate of cosmic expansion.<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup></p> <p>The rate of cosmic expansion is described by the Hubble parameter, which we can measure to within a few percent. Unfortunately, our various methods of measure are now so precise their uncertainties don&rsquo;t overlap. This contradiction in values is known as the <a href="https://briankoberlein.com/blog/then-things-got-worse/">Hubble tension.</a> Several re-evaluations of our methods have ruled out systematic error, so astronomers look to new independent ways to measure the Hubble parameter, which is where a new study comes in.</p> <figure class="right"> <a href="https://briankoberlein.com/blog/fast-and-far/figure.png"> <span class="credit"> <img srcset=' /blog/fast-and-far/figure_hu706ecae4e1e4607e6ddd1248c9d7c14c_252905_300x0_resize_box_3.png 300w , /blog/fast-and-far/figure_hu706ecae4e1e4607e6ddd1248c9d7c14c_252905_350x0_resize_box_3.png 350w , /blog/fast-and-far/figure_hu706ecae4e1e4607e6ddd1248c9d7c14c_252905_550x0_resize_box_3.png 550w , /blog/fast-and-far/figure_hu706ecae4e1e4607e6ddd1248c9d7c14c_252905_600x0_resize_box_3.png 600w , /blog/fast-and-far/figure_hu706ecae4e1e4607e6ddd1248c9d7c14c_252905_700x0_resize_box_3.png 700w , /blog/fast-and-far/figure_hu706ecae4e1e4607e6ddd1248c9d7c14c_252905_1100x0_resize_box_3.png 1100w ' src="https://briankoberlein.com/blog/fast-and-far/figure_hu706ecae4e1e4607e6ddd1248c9d7c14c_252905_300x0_resize_box_3.png" loading="lazy" width="1620" height="1454" alt="The geometry of an FRB measurement."/> <span class="attribution">Tsai, et al</span></span> </a> <figcaption>The geometry of an FRB measurement.</figcaption> </figure> <p>The paper looks at using FRBs as a Hubble measure. For light from an FRB to reach us, it needs to travel millions of light-years through the diffuse intergalactic and interstellar medium. This causes the frequency of the light to spread out. The amount of spectral spreading is known as the <a href="https://briankoberlein.com/post/cosmic-corn-syrup/">Dispersion Measure (DM),</a> and the greater the DM the greater the distance. So we know the distance to FRBs. But to measure cosmic expansion, we also need a second distance measure, and here the paper proposes using gravitational lensing.</p> <p>If the FRB light path passes relatively close to a massive object such as a star, the light can be gravitationally lensed around the object. From the width of the lensing, we have an idea of its relative distance to the FRB source. When the FRB light passes from the intergalactic medium to the more dense interstellar medium of our galaxy, there is a brightening effect known as scintillation, which gives us another distance measure A bit of geometry then allows us to calculate the Hubble parameter.</p> <p>Based on their calculations, the authors estimate that a single lensed FRB observation would allow them to pin down the Hubble parameter to within 6% accuracy. With 30 or more events, they should be able to increase their precision to a fraction of a percent uncertainty. This would put it on par with other methods. This should be achievable given current and planned FRB telescopes.</p> <p>New observation methods such as this are the only way we are going to resolve the Hubble tension. Hopefully, we will solve this mystery, and perhaps it will point us to a radically new understanding of cosmic evolution.</p> <div class="footnotes" role="doc-endnotes"> <hr> <ol> <li id="fn:1"> <p>Tsai, Anna, et al. &ldquo;Scintillated microlensing: measuring cosmic distances with fast radio bursts.&rdquo; <em>arXiv preprint</em> arXiv:2308.10830 (2023).&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> </ol> </div>Jets on the Edgehttps://briankoberlein.com/blog/jets-on-the-edge/Sat, 10 Feb 2024 10:39:07 +0000https://briankoberlein.com/blog/jets-on-the-edge/ <figure class=""> <a href="https://briankoberlein.com/blog/jets-on-the-edge/jets.jpg"> <span class="credit"> <img srcset=' /blog/jets-on-the-edge/jets_huc18637f07adb2ddfef566333318037ca_226089_300x0_resize_q75_box.jpg 300w , /blog/jets-on-the-edge/jets_huc18637f07adb2ddfef566333318037ca_226089_550x0_resize_q75_box.jpg 550w , /blog/jets-on-the-edge/jets_huc18637f07adb2ddfef566333318037ca_226089_700x0_resize_q75_box.jpg 700w , /blog/jets-on-the-edge/jets_huc18637f07adb2ddfef566333318037ca_226089_900x0_resize_q75_box.jpg 900w , /blog/jets-on-the-edge/jets_huc18637f07adb2ddfef566333318037ca_226089_1100x0_resize_q75_box.jpg 1100w , /blog/jets-on-the-edge/jets_huc18637f07adb2ddfef566333318037ca_226089_1400x0_resize_q75_box.jpg 1400w , /blog/jets-on-the-edge/jets_huc18637f07adb2ddfef566333318037ca_226089_1800x0_resize_q75_box.jpg 1800w ' src="https://briankoberlein.com/blog/jets-on-the-edge/jets_huc18637f07adb2ddfef566333318037ca_226089_300x0_resize_q75_box.jpg" loading="lazy" width="2800" height="2085" alt="The jet of the black hole in 3C 84 at different spatial scales."/> <span class="attribution">Georgios Filippos Paraschos (MPIfR)</span></span> </a> <figcaption>The jet of the black hole in 3C 84 at different spatial scales.</figcaption> </figure> <p>Although supermassive black holes are common throughout the Universe, we don&rsquo;t have many direct images of them. The problem is that while they can have a mass of millions or billions of stars, even the nearest supermassive black holes have tiny apparent sizes. The only direct images we have are those of <a href="https://briankoberlein.com/blog/together-we-can/">M87*</a> and <a href="https://briankoberlein.com/blog/spin-doctor/">Sag A*,</a> and it took a virtual telescope the size of Earth to capture them. But we are still in the early days of the Event Horizon Telescope (EHT), and improvements are being made to the virtual telescope all the time. Which means we are starting to look at more supermassive black holes.<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup></p> <p>The latest observations focus on a black hole region known as 3C 84, or Perseus A. It is a radio-bright source in a galaxy more than 200 million light-years away. Even the latest iteration of the EHT can&rsquo;t resolve the horizon glow of the black hole as we&rsquo;ve done with M87* and Sag A*, but it can see the bright region surrounding the black hole, where magnetic fields are particularly intense.</p> <figure class="right"> <a href="https://briankoberlein.com/blog/jets-on-the-edge/ngc1275.jpg"> <span class="credit"> <img srcset=' /blog/jets-on-the-edge/ngc1275_huedbde2733d6284f4d96cc240cb5436e5_181101_300x0_resize_q75_box.jpg 300w , /blog/jets-on-the-edge/ngc1275_huedbde2733d6284f4d96cc240cb5436e5_181101_350x0_resize_q75_box.jpg 350w , /blog/jets-on-the-edge/ngc1275_huedbde2733d6284f4d96cc240cb5436e5_181101_550x0_resize_q75_box.jpg 550w , /blog/jets-on-the-edge/ngc1275_huedbde2733d6284f4d96cc240cb5436e5_181101_600x0_resize_q75_box.jpg 600w , /blog/jets-on-the-edge/ngc1275_huedbde2733d6284f4d96cc240cb5436e5_181101_700x0_resize_q75_box.jpg 700w ' src="https://briankoberlein.com/blog/jets-on-the-edge/ngc1275_huedbde2733d6284f4d96cc240cb5436e5_181101_300x0_resize_q75_box.jpg" loading="lazy" width="1024" height="1024" alt="A wide multi-wavelength composite view of NGC 1275."/> <span class="attribution">Marie-Lou Gendron-Marsolais (Université de Montréal), Julie Hlavacek-Larrondo (Université de Montréal), Maxime Pivin Lapointe</span></span> </a> <figcaption>A wide multi-wavelength composite view of NGC 1275.</figcaption> </figure> <p>The 3C 84 black hole is located in the galaxy NGC 1275, which is part of the Perseus cluster. The galaxy is not just distant, it also has a central region rich in dust, which shrouds the black hole. Optical light can&rsquo;t penetrate the region, but radio light can. The Event Horizon Telescope can also capture the polarization of radio light coming from the area. This is important because charged particles within a strong magnetic field emit polarized light. By mapping this polarization astronomers can study magnetic fields.</p> <p>One focus of this work is to see how supermassive black holes can generate powerful jets that stream from the black hole at nearly the speed of light. Magnetic fields are key. As ionized matter falls into a black hole it can bring with it strong magnetic fields. These fields can pin to the accretion disk of a black hole, which intensifies fields in the region that it becomes difficult for the black hole to capture more matter. This is known as a magnetically arrested disk.</p> <p>One idea is that as the magnetically arrested disk rotates around the black hole, magnetic field lines become twisted, winding ever tighter and trapping magnetic energy. The release of this energy through magnetic realignment could power the formation of ionized jets. While such a magnetic realignment hasn&rsquo;t been observed, this study shows that we might be able to capture such an event.</p> <div class="footnotes" role="doc-endnotes"> <hr> <ol> <li id="fn:1"> <p>Paraschos, G. F., et al. &ldquo;Ordered magnetic fields around the 3C 84 central black hole.&rdquo; <em>Astronomy &amp; Astrophysics</em> 682 (2024): L3.&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> </ol> </div>Discovering Life on Planet Earthhttps://briankoberlein.com/blog/discovering-life-on-planet-earth/Thu, 08 Feb 2024 13:28:54 +0000https://briankoberlein.com/blog/discovering-life-on-planet-earth/ <figure class=""> <a href="https://briankoberlein.com/blog/discovering-life-on-planet-earth/earth.jpg"> <span class="credit"> <img srcset=' /blog/discovering-life-on-planet-earth/earth_hu33b9abb5dd0c35c0eec090265eae2e83_61799_300x0_resize_q75_box.jpg 300w , /blog/discovering-life-on-planet-earth/earth_hu33b9abb5dd0c35c0eec090265eae2e83_61799_550x0_resize_q75_box.jpg 550w , /blog/discovering-life-on-planet-earth/earth_hu33b9abb5dd0c35c0eec090265eae2e83_61799_700x0_resize_q75_box.jpg 700w , /blog/discovering-life-on-planet-earth/earth_hu33b9abb5dd0c35c0eec090265eae2e83_61799_900x0_resize_q75_box.jpg 900w , /blog/discovering-life-on-planet-earth/earth_hu33b9abb5dd0c35c0eec090265eae2e83_61799_1100x0_resize_q75_box.jpg 1100w , /blog/discovering-life-on-planet-earth/earth_hu33b9abb5dd0c35c0eec090265eae2e83_61799_1400x0_resize_q75_box.jpg 1400w ' src="https://briankoberlein.com/blog/discovering-life-on-planet-earth/earth_hu33b9abb5dd0c35c0eec090265eae2e83_61799_300x0_resize_q75_box.jpg" loading="lazy" width="1600" height="800" alt="An image of Earth taken by the Galileo spacecraft in 1990."/> <span class="attribution">NASA/JPL</span></span> </a> <figcaption>An image of Earth taken by the Galileo spacecraft in 1990.</figcaption> </figure> <p>In the Fall of 1989, the Galileo spacecraft was launched into space, bound for Jupiter and its family of moons. Given the great distance to the king of planets, Galileo had to take a roundabout tour through the inner solar system, making a flyby of Venus in 1990 and Earth in 1990 and 1992 just to gain enough speed to reach Jupiter. During the flybys of Earth Galileo took several images of our planet, which astronomers have used to discover life on Earth.<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup></p> <p>The idea of &ldquo;discovering&rdquo; life on Earth in the 21st century might seem a bit ridiculous, but the study is quite useful to astronomers seeking life on other worlds. Since we know there is life on Earth as well as the geography and diversity of our world, images from Galileo can be used as a test bed to compare with images of exoplanets. We are still in the early stages of making direct images of some exoplanets, and astronomers are still learning what those images might tell us.</p> <figure class="center"> <a href="https://briankoberlein.com/blog/discovering-life-on-planet-earth/pixels.jpg"> <span class="credit"> <img srcset=' /blog/discovering-life-on-planet-earth/pixels_hu7990b71cf843c19ed86007464bd19062_57558_550x0_resize_q75_box.jpg 550w , /blog/discovering-life-on-planet-earth/pixels_hu7990b71cf843c19ed86007464bd19062_57558_700x0_resize_q75_box.jpg 700w , /blog/discovering-life-on-planet-earth/pixels_hu7990b71cf843c19ed86007464bd19062_57558_1100x0_resize_q75_box.jpg 1100w ' src="https://briankoberlein.com/blog/discovering-life-on-planet-earth/pixels_hu7990b71cf843c19ed86007464bd19062_57558_300x0_resize_q75_box.jpg" loading="lazy" width="1200" height="675" alt="A detailed image of Earth vs how it would appear as a distant exoplanet."/> <span class="attribution">NOAA/NASA/Stephen Kane</span></span> </a> <figcaption>A detailed image of Earth vs how it would appear as a distant exoplanet.</figcaption> </figure> <p>So in this work, the team focused on what are known as disk-integrated images. This is where light from a planet is taken as a whole. Instead of a detailed image of Earth such as the one above, the team looked at integrated images from the Limited Solid State Imager (SSI). The disk-integrated images it gathers are similar to the images we can capture of exoplanets. They then looked at the overall brightness and spectra of these images to see what they could tell us about Earth.</p> <p>One of the things the authors found is that much of the spectral data in the integrated images is washed out, making it difficult to identify particular biosignatures. That was somewhat expected since the Galileo cameras were optimized for Jupiter, which is much more distant from the Sun and therefore much dimmer. However, the team was able to detect an oxygen absorption line, verifying that our planet has an oxygen-rich atmosphere. By itself the presence of oxygen <a href="https://briankoberlein.com/blog/life-as-we-know-it/">wouldn&rsquo;t conclusively prove that life exists on Earth,</a> but it is a good start.</p> <figure class="center"> <a href="https://briankoberlein.com/blog/discovering-life-on-planet-earth/terrain.jpg"> <span class="credit"> <img srcset=' /blog/discovering-life-on-planet-earth/terrain_hue71219f89a2bd77b59b125a4d9fea235_157591_550x0_resize_q75_box.jpg 550w , /blog/discovering-life-on-planet-earth/terrain_hue71219f89a2bd77b59b125a4d9fea235_157591_700x0_resize_q75_box.jpg 700w , /blog/discovering-life-on-planet-earth/terrain_hue71219f89a2bd77b59b125a4d9fea235_157591_1100x0_resize_q75_box.jpg 1100w , /blog/discovering-life-on-planet-earth/terrain_hue71219f89a2bd77b59b125a4d9fea235_157591_1400x0_resize_q75_box.jpg 1400w ' src="https://briankoberlein.com/blog/discovering-life-on-planet-earth/terrain_hue71219f89a2bd77b59b125a4d9fea235_157591_300x0_resize_q75_box.jpg" loading="lazy" width="1830" height="940" alt="How brightness ratios of red/violet and UV/violet show evidence of Earth&#39;s terrain."/> <span class="attribution">Strauss, et al</span></span> </a> <figcaption>How brightness ratios of red/violet and UV/violet show evidence of Earth&rsquo;s terrain.</figcaption> </figure> <p>More interestingly, the team was able to look at the changes in albedo, or reflective brightness as Earth rotates. From this, they could get a very rough idea of continents and oceans on Earth. From this they could prove that Earth has a mixture of both lands and oceans, making it well-suited for habitability.</p> <p>The biggest benefit of this study and others like it is that it provides a baseline for potentially habitable exoplanets. Seen from a distance and with limited resolution, this is how a life-bearing planet appears. As astronomers find exoplanets that appear similar, they will know they are on the right track to discovering life on other worlds.</p> <div class="footnotes" role="doc-endnotes"> <hr> <ol> <li id="fn:1"> <p>Strauss, Ryder H., et al. &ldquo;Exoplanet Analog Observations of Earth from Galileo Disk-integrated Photometry.&rdquo; <em>The Astronomical Journal</em> 167.3 (2024): 87.&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> </ol> </div>The Dust of Timehttps://briankoberlein.com/blog/dust-of-time/Wed, 07 Feb 2024 08:22:40 +0000https://briankoberlein.com/blog/dust-of-time/ <figure class=""> <a href="https://briankoberlein.com/blog/dust-of-time/heic1006a.jpg"> <span class="credit"> <img srcset=' /blog/dust-of-time/heic1006a_hu83ef240247c10c86705002b3b80f20ea_3517861_300x0_resize_q75_box.jpg 300w , /blog/dust-of-time/heic1006a_hu83ef240247c10c86705002b3b80f20ea_3517861_550x0_resize_q75_box.jpg 550w , /blog/dust-of-time/heic1006a_hu83ef240247c10c86705002b3b80f20ea_3517861_700x0_resize_q75_box.jpg 700w , /blog/dust-of-time/heic1006a_hu83ef240247c10c86705002b3b80f20ea_3517861_900x0_resize_q75_box.jpg 900w , /blog/dust-of-time/heic1006a_hu83ef240247c10c86705002b3b80f20ea_3517861_1100x0_resize_q75_box.jpg 1100w , /blog/dust-of-time/heic1006a_hu83ef240247c10c86705002b3b80f20ea_3517861_1400x0_resize_q75_box.jpg 1400w , /blog/dust-of-time/heic1006a_hu83ef240247c10c86705002b3b80f20ea_3517861_1800x0_resize_q75_box.jpg 1800w ' src="https://briankoberlein.com/blog/dust-of-time/heic1006a_hu83ef240247c10c86705002b3b80f20ea_3517861_300x0_resize_q75_box.jpg" loading="lazy" width="3903" height="2702" alt="A dusty spiral galaxy known as M66."/> <span class="attribution">NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble</span></span> </a> <figcaption>A dusty spiral galaxy known as M66.</figcaption> </figure> <p>Astronomers have many ways to measure the distance to galaxies billions of light years away, but most of them rely upon <a href="https://briankoberlein.com/blog/climbing-the-ladder/">standard candles.</a> These are astrophysical processes that have a brightness we can calibrate, such as Cepheid variable stars or Type Ia supernovae. Of course, all of these standard candles have some inherent variability, so astronomers also look for where our assumptions about them can lead us astray. As a case in point, a recent study in <em>The Astrophysical Journal</em> shows how galactic dust can bias distance observations.<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup></p> <p>The study compares two slightly different ways to measure galactic distances. The first method compares the X-ray luminosity of a galaxy to its brightness at ultraviolet wavelengths. Known as L<sub>X</sub>–L<sub>UV</sub>, this approach relies on the fact that active galactic nuclei (AGNs) have a similar spectrum depending on their overall brightness. The L<sub>X</sub>–L<sub>UV</sub> allows astronomers to determine the absolute magnitude, and therefore galactic distance. The second method is known as R - L and compares the ultraviolet luminosity of the accretion disk around the galaxy&rsquo;s supermassive black hole with the radius of that accretion disk. The bigger the disk, the brighter it is, thus getting the absolute magnitude.</p> <p>Both of these methods focus on the brightness of the AGN, and both involve UV brightness, so both methods should give us a similar distance. But often they don&rsquo;t. The authors of this paper wanted to find out why, so they looked at 58 galaxies where both methods had been used to determine their distance. They then looked for factors that might skew the results of one method relative to the other.</p> <p>The team found that dust within a galaxy can affect the L<sub>X</sub>–L<sub>UV</sub> method. Galactic dust, mostly made of carbon and silicon, can absorb X-ray light and re-emit other wavelengths. The more dusty a galaxy is, the more significantly it can skew the distance result. The team also found that the presence of dust doesn&rsquo;t significantly bias the R - L method. Based on this, the authors recommend that the L<sub>X</sub>–L<sub>UV</sub> method not be used to measure galactic distances. That&rsquo;s a little unfortunate since the R - L method is a bit more difficult to measure, but it means we can rule out data that could be skewing our cosmic distance measures. This could help us better understand the underlying issues of the <a href="https://briankoberlein.com/blog/inherent-in-the-system/">Hubble tension,</a> which continues to nag cosmologists.</p> <p>The discovery of this bias doesn&rsquo;t in any way undermine the standard model of cosmology, as these methods aren&rsquo;t the only ones we can use to determine cosmic distances. Instead, it further improves our methods, so that we now have an even clearer understanding of how our Universe came to be.</p> <div class="footnotes" role="doc-endnotes"> <hr> <ol> <li id="fn:1"> <p>Zajaček, Michal, et al. &ldquo;Effect of Extinction on Quasar Luminosity Distances Determined from UV and X-Ray Flux Measurements.&rdquo; <em>The Astrophysical Journal</em> 961.2 (2024): 229.&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> </ol> </div>Defying Gravityhttps://briankoberlein.com/blog/defying-gravity/Tue, 06 Feb 2024 09:26:35 +0000https://briankoberlein.com/blog/defying-gravity/ <figure class=""> <a href="https://briankoberlein.com/blog/defying-gravity/milkyway.jpg"> <span class="credit"> <img srcset=' /blog/defying-gravity/milkyway_hud91713f9515d42ffd2ae6ca2fb9d95f6_281032_300x0_resize_q75_box.jpg 300w , /blog/defying-gravity/milkyway_hud91713f9515d42ffd2ae6ca2fb9d95f6_281032_550x0_resize_q75_box.jpg 550w , /blog/defying-gravity/milkyway_hud91713f9515d42ffd2ae6ca2fb9d95f6_281032_700x0_resize_q75_box.jpg 700w , /blog/defying-gravity/milkyway_hud91713f9515d42ffd2ae6ca2fb9d95f6_281032_900x0_resize_q75_box.jpg 900w , /blog/defying-gravity/milkyway_hud91713f9515d42ffd2ae6ca2fb9d95f6_281032_1100x0_resize_q75_box.jpg 1100w , /blog/defying-gravity/milkyway_hud91713f9515d42ffd2ae6ca2fb9d95f6_281032_1400x0_resize_q75_box.jpg 1400w , /blog/defying-gravity/milkyway_hud91713f9515d42ffd2ae6ca2fb9d95f6_281032_1800x0_resize_q75_box.jpg 1800w ' src="https://briankoberlein.com/blog/defying-gravity/milkyway_hud91713f9515d42ffd2ae6ca2fb9d95f6_281032_300x0_resize_q75_box.jpg" loading="lazy" width="1922" height="1080" alt="Artist view of the Milky Way galaxy."/> <span class="attribution">ESA</span></span> </a> <figcaption>Artist view of the Milky Way galaxy.</figcaption> </figure> <p>If you want to determine your mass, it&rsquo;s pretty easy. Just step on a scale and look at the number it gives you. That number tells you the gravitational pull of Earth upon you, so if you feel the number is too high, take comfort that Earth just finds you more attractive than others. The same scale could also be used to measure the mass of Earth. If you place a <a href="https://archive.briankoberlein.com/2017/07/16/the-magic-rock/index.html">kilogram mass</a> on the scale, the weight it gives is also the weight of Earth in the gravitational field of the kilogram. With a bit of mass, you have the mass of Earth.</p> <p>Things aren&rsquo;t quite that simple. The Earth is not a perfectly spherical, perfectly uniform mass, so its gravitational pull <a href="https://briankoberlein.com/blog/potsdam-gravity-potato/">varies slightly across the globe.</a> But this method gives a reasonable ballpark value, and we can use it to estimate the masses of other objects in the solar system. But how can we determine the mass of something larger, such as the Milky Way? One method is to estimate the number of stars in the galaxy and their masses, then estimate the mass of all the interstellar gas and dust, and then rough out the amount of dark matter&hellip; It all gets very complicated.</p> <p>A better way is to look at how the orbital speed of stars <a href="https://briankoberlein.com/blog/lighter-story/">varies with distance from the galactic center.</a> This is known as the rotation curve and gives an upper mass limit on the Milky Way, which seems to be around 600 billion to a trillion solar masses. The wide uncertainty gives you an idea of just how difficult it is to measure our galaxy&rsquo;s mass. But a new study introduces a new method, and it could help astronomers pin things down.<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup></p> <figure class="center"> <a href="https://briankoberlein.com/blog/defying-gravity/x1.png"> <span class="credit"> <img srcset=' /blog/defying-gravity/x1_hu434aa8bb506e21e1ca4a3bee2af5e06d_304802_550x0_resize_box_3.png 550w , /blog/defying-gravity/x1_hu434aa8bb506e21e1ca4a3bee2af5e06d_304802_700x0_resize_box_3.png 700w , /blog/defying-gravity/x1_hu434aa8bb506e21e1ca4a3bee2af5e06d_304802_1100x0_resize_box_3.png 1100w , /blog/defying-gravity/x1_hu434aa8bb506e21e1ca4a3bee2af5e06d_304802_1400x0_resize_box_3.png 1400w ' src="https://briankoberlein.com/blog/defying-gravity/x1_hu434aa8bb506e21e1ca4a3bee2af5e06d_304802_300x0_resize_box_3.png" loading="lazy" width="1661" height="830" alt="Estimated escape velocities at different galactic radii."/> <span class="attribution">Roche, et al</span></span> </a> <figcaption>Estimated escape velocities at different galactic radii.</figcaption> </figure> <p>The method looks at the <a href="https://briankoberlein.com/blog/galactic-scales/">escape velocity</a> of stars in our galaxy. If a star is moving fast enough, it can overcome the gravitational pull of the Milky Way and escape into interstellar space. The minimum speed necessary to escape depends upon our galaxy&rsquo;s mass, so measuring one gives you the other. Unfortunately, only a handful of stars are known to be escaping, which is not enough to get a good handle on galactic mass. So the team looked at the statistical distribution of stellar speeds as measured by the Gaia spacecraft.</p> <p>The method is similar to weighing the Moon with a handful of dust. If you were standing on the Moon and tossed dust upward, the slower-moving dust particles would reach a lower height than faster particles. If you measured the speeds and positions of the dust particles, the statistical relation between speed and height would tell you how strongly the Moon pulls on the motes, and thus the mass of the Moon. It would be easier just to bring our kilogram and scale to measure lunar mass, but the dust method could work.</p> <p>In the Milky Way, the stars are like dustmotes, swirling around in the gravitational field of the galaxy. The team used the speeds and positions of a billion stars to estimate the escape velocity at different distances from the galactic center. From that, they could determine the overall mass of the Milky Way. They calculated a mass of 640 billion Suns.</p> <p>This is on the lower end of earlier estimates, and if accurate it means that the Milky Way has a bit less dark matter than we thought.</p> <div class="footnotes" role="doc-endnotes"> <hr> <ol> <li id="fn:1"> <p>Roche, Cian, et al. &ldquo;The Escape Velocity Profile of the Milky Way from Gaia DR3.&rdquo; <em>arXiv preprint</em> arXiv:2402.00108 (2024).&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> </ol> </div>Balancing on a Beamhttps://briankoberlein.com/blog/balancing-on-a-beam/Sun, 04 Feb 2024 14:58:02 +0000https://briankoberlein.com/blog/balancing-on-a-beam/ <figure class=""> <a href="https://briankoberlein.com/blog/balancing-on-a-beam/lightsail.jpg"> <span class="credit"> <img srcset=' /blog/balancing-on-a-beam/lightsail_hu19069de22d2cfbfef8a134af1ddb2e08_694578_300x0_resize_q75_box.jpg 300w , /blog/balancing-on-a-beam/lightsail_hu19069de22d2cfbfef8a134af1ddb2e08_694578_550x0_resize_q75_box.jpg 550w , /blog/balancing-on-a-beam/lightsail_hu19069de22d2cfbfef8a134af1ddb2e08_694578_700x0_resize_q75_box.jpg 700w , /blog/balancing-on-a-beam/lightsail_hu19069de22d2cfbfef8a134af1ddb2e08_694578_900x0_resize_q75_box.jpg 900w ' src="https://briankoberlein.com/blog/balancing-on-a-beam/lightsail_hu19069de22d2cfbfef8a134af1ddb2e08_694578_300x0_resize_q75_box.jpg" loading="lazy" width="940" height="870" alt="Artist concept of an interstellar light sail."/> <span class="attribution">Breakthrough Initiative</span></span> </a> <figcaption>Artist concept of an interstellar light sail.</figcaption> </figure> <p>It&rsquo;s a long way to the nearest star, which means conventional rockets won&rsquo;t get us there. The fuel requirements would make our ship prohibitively heavy. So an alternative is to travel light. Literally. Rather than carrying your fuel with you, simply attach your tiny starship to a large reflective sail, and shine a powerful laser at it. The impulse of photons would push the starship to a fraction of light speed. Riding a beam of light, a light sail mission could reach Proxima Centauri in a couple of decades. But while the idea is simple, the engineering challenges are significant, because, across decades and light-years, even the smallest problem can be difficult to solve.</p> <p>One example of this can be seen in a recent <em>arXiv</em> paper.<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup> It looks at the problem of how to balance a light sail on a laser beam. Although the laser could be aimed directly toward a star, or where it will be in a couple of decades, the light sail would only follow the beam if it is perfectly balanced. If a sail is slightly tilted relative to the beam, the reflected laser light would give the light sail a slight transverse push. No matter how small this deviation is, it would grow over time, causing its path to drift ever away from its target. We will never align a light sail perfectly, so we need some way to correct small deviations.</p> <figure class="right"> <a href="https://briankoberlein.com/blog/balancing-on-a-beam/deviation.jpg"> <span class="credit"> <img srcset=' /blog/balancing-on-a-beam/deviation_hu3c0700c05655df6f2250dd3a8c510ee8_179494_300x0_resize_q75_box.jpg 300w , /blog/balancing-on-a-beam/deviation_hu3c0700c05655df6f2250dd3a8c510ee8_179494_350x0_resize_q75_box.jpg 350w , /blog/balancing-on-a-beam/deviation_hu3c0700c05655df6f2250dd3a8c510ee8_179494_550x0_resize_q75_box.jpg 550w , /blog/balancing-on-a-beam/deviation_hu3c0700c05655df6f2250dd3a8c510ee8_179494_600x0_resize_q75_box.jpg 600w , /blog/balancing-on-a-beam/deviation_hu3c0700c05655df6f2250dd3a8c510ee8_179494_700x0_resize_q75_box.jpg 700w , /blog/balancing-on-a-beam/deviation_hu3c0700c05655df6f2250dd3a8c510ee8_179494_1100x0_resize_q75_box.jpg 1100w ' src="https://briankoberlein.com/blog/balancing-on-a-beam/deviation_hu3c0700c05655df6f2250dd3a8c510ee8_179494_300x0_resize_q75_box.jpg" loading="lazy" width="1750" height="1312" alt="How a small deviation can send a light sail off course."/> <span class="attribution">Mackintosh, et al</span></span> </a> <figcaption>How a small deviation can send a light sail off course.</figcaption> </figure> <p>For traditional rockets, this can be done with internal gyroscopes to stabilize the rocket, and engines that can dynamically adjust their thrust to restore balance. But a gyro system would be too heavy for an interstellar light sail, and adjustments of the beam would take months or years to reach the light sail, making quick changes impossible. So the authors suggest using a radiative trick known as the Poynting–Robertson effect.</p> <figure class="left"> <a href="https://briankoberlein.com/blog/balancing-on-a-beam/pr.jpg"> <span class="credit"> <img srcset=' /blog/balancing-on-a-beam/pr_huc1aa1d7b6ccf1482c5175afc194e79f7_110857_300x0_resize_q75_box.jpg 300w , /blog/balancing-on-a-beam/pr_huc1aa1d7b6ccf1482c5175afc194e79f7_110857_350x0_resize_q75_box.jpg 350w , /blog/balancing-on-a-beam/pr_huc1aa1d7b6ccf1482c5175afc194e79f7_110857_550x0_resize_q75_box.jpg 550w , /blog/balancing-on-a-beam/pr_huc1aa1d7b6ccf1482c5175afc194e79f7_110857_600x0_resize_q75_box.jpg 600w , /blog/balancing-on-a-beam/pr_huc1aa1d7b6ccf1482c5175afc194e79f7_110857_700x0_resize_q75_box.jpg 700w ' src="https://briankoberlein.com/blog/balancing-on-a-beam/pr_huc1aa1d7b6ccf1482c5175afc194e79f7_110857_300x0_resize_q75_box.jpg" loading="lazy" width="1024" height="712" alt="How relative motion affects sunlight on a dust grain."/> <span class="attribution">Michael Schmid, via Wikipedia</span></span> </a> <figcaption>How relative motion affects sunlight on a dust grain.</figcaption> </figure> <p>The effect was first studied in the early 1900s and is caused by the relative motion between an object and a light source. For example, a dust grain orbiting the Sun sees light coming at a slight forward angle due to its motion through sunlight. That little forward component of light can slow down the asteroid ever so slightly. This effect causes dust to drift toward the inner solar system over time.</p> <p>In this paper, the authors consider a two-dimensional model to see how the Poynting–Robertson effect might be used to keep our light sail probe on course. To keep things simple, they assumed the light beam to be a simple monochromatic plane wave. Real lasers are more complex, but the assumption is reasonable for a proof of concept. They then showed how a simple two-sail system can use the effects of relative motion to keep the craft in balance. As the sails tilt off course slightly, a restorative force from the beam counters it. Thus proving the concept could work.</p> <p>However, the authors noticed that over time the effects of relativity come into play. Earlier studies have taken the Doppler effect of relative motion into effect, but this study shows the relativistic version of chromatic aberration would also come into play. The full relativistic effects would need to be accounted for in a realistic design, which would require sophisticated modeling and optics.</p> <p>So a light sail still seems like a possible way to reach the stars. We just have to be careful not to make light of the engineering challenges.</p> <div class="footnotes" role="doc-endnotes"> <hr> <ol> <li id="fn:1"> <p>Mackintosh, Rhys, et al. &ldquo;Poynting-Robertson damping of laser beam driven lightsails.&rdquo; <em>arXiv preprint</em> arXiv:2401.16924 (2024).&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p> </li> </ol> </div>