###### Newsletter

# An August Season

2 August 2021

This past month has been a very light one in terms of posts. Between visiting my parents, Summer housework, and other life events, I didn’t have as much time to write.

#### A Wave of New Findings

Astronomers observed not one, but two mergers between a black hole and a neutron star. These types of mergers will allow astronomers to study the interiors of neutron stars, which we still don’t understand very well.

Black hole mergers also helped astronomers prove a long-standing theory about black holes, known as Hawking’s Area Theorem. The theorem states that when two black holes merge, the event horizon area of the resulting black hole must be greater than the areas of the original two combined. Based on observations, the theorem seems to be true. This also means that the laws of thermodynamics apply to black holes as well, leading to things such as Hawking radiation.

In cosmology, astronomers have had difficulty determining just how fast the universe is expanding. We have a good general idea, but we can’t pin down the exact value. That’s because different measurement methods give slightly different results. This is known as the cosmic tension problem. But new work shows this tension isn’t as bad as we’d thought.

Finally, given the power of gravitational wave astronomy, it’s reasonable to develop new and more powerful gravitational wave telescopes. Space-based telescopes have been proposed before, but a new paper argues that a Moon-based gravity telescope would be extremely useful. Such a telescope could be built in the next couple of decades and would lead to amazing new discoveries.

#### Until Next Time

There will be more blog posts in August, but until then I hope you enjoy the Summer season (if you’re in the Northern Hemisphere).