The Power of Observation

X-ray: NASA/CXC/Penn State Univ./L. Townsley et al.; Optical: NASA/STScI/HST; Infrared: NASA/JPL/CalTech/SST

The key to astronomy is careful observation. Unlike many sciences, astronomers can’t often do their work in a lab. Sure, they can build space telescopes and large ground observatories, but even with tools as simple as sticks and stones astronomers were able to change our understanding of the Universe with patience and observation. That tradition still holds true today, as a recent study in The Astronomical Journal shows.¹

The study focuses on a small nebula in the southern hemisphere known as 30 Doradus B. It is part of a star-forming region that has been creating stars for about 10 million years. At first glance, 30 Dor B is a rather typical nebula. It’s a supernova remnant in the Large Magellanic Cloud, but otherwise not much to look at. However, interesting things can be discovered if you take the time to look.

In this case, the team looked at x-ray data captured by the Chandra space telescope. Two million seconds worth of data, which adds up to more than 23 days. From these weeks of data, they were able to detect a faint shell gas emitting X-rays. The shell is about 130 light-years across, which is large, but again not too unusual. X-ray shells such as this are often seen around supernova remnants. When supernovae explode they cast off a shell of high-velocity material, which can collide with interstellar gas to produce X-rays.

But the team went further, and looked at Hubble observations of the region in visible light, and other observations in infrared. By combining all of this data they began to see something strange. The visible and infrared observations show the distribution of gas in the nebula, and combined with x-ray data of the same region they could show that the supernova occurred about 5,000 years ago. But the extended shell of faint X-rays is too large to match that age. Based on the size of the X-ray shell, there must have been a supernova explosion more than 5,000 years ago.

Taken together, the observations revealed that 30 Doradus B is not a simple supernova. Instead, it is the product of at least two supernovae occurring within the same region. It’s possible that the first supernova helped to trigger the second one. It’s even possible that multiple supernovae occurred in the region over the past several millennia.

Of course, none of this is obvious to look at the nebula. If this team of astronomers hadn’t taken a second look we would just assume it is a typical remnant. But because of their detailed study, we can learn more about the evolution and demise of large stars in star-forming regions. Careful observation leads to beautiful data, and our understanding of the cosmos is all the richer for it.