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What happens when astronomers use Chandra to take a long look at the same patch of sky? (2017-01-06)

Peering Into the X-ray Future

This year marks 10 years since Chandra was launched and deployed from the Space Shuttle Columbia. Such a milestone not only gives us a chance to look back, but it also provides an opportunity to think about what lies ahead. This episode will touch on some of the areas in which astronomers hope X-ray telescopes will push our knowledge forward in the years to come. To help us explore some of these topics, Dr. Randall Smith joins us. Randall is an astrophysicist working with the International X-ray Observatory. This is a proposed mission that would be a joint project of NASA, the European Space Agency, and the Japanese Space Agency, that would be developed and launched in the decades to come.

While Chandra and XMM-Newton have been even better than we'd hoped, we as scientists are always looking at the next questions to answer. In the case of X-ray astronomy, we've got some great questions to ask. Let me begin with what we're going to be able to do with black holes. With a new, much bigger X-ray telescope, we're going to watch as the very first black holes in the Universe grow into giant black holes. It's surprisingly difficult for a black hole to grow very fast. They tend to spit back if fed too quickly. We'll be able to watch them as they develop and see how it works -- something that's a huge unknown right now. Also, well be able to track material zooming around black holes that's very close to the point of no return. While, of course, we can't see anything that's fallen into the black hole, we can tell a lot about it, like whether the black hole itself is spinning or not, based on what's happening with these clumps zooming around just outside it.

So black holes are one huge area that X-ray telescopes are necessary to study. What are some of the others?

X-ray telescopes are unique in that they can see really hot material. Fortunately, the Universe is full of hot stuff, of all sizes. On the big end, the largest individual 'things' in the Universe are clusters of galaxies, and in these galaxy clusters just about all of the mass comes in the form of very hot gas. So X-rays tell us a lot about what is happening in these clusters, how they formed, what's in them, where they're going, and so on. In other words, in order to understand what's happening in the Universe, a good place to start is these clusters of galaxies. Current X-ray observations have shown, for example, that there is a connection between these clusters and the - relatively speaking, much smaller - black holes at their centers. We expect the next generation of X-ray telescopes will help us understand this relationship far better than we do now. The key thing to understand is that these interactions are taking place over colossal scales. Even though we've made enormous progress in the past decade with Chandra, there are just so many questions we still don't have answers for.

It's clear that X-ray astronomy is crucial to understanding some of the very biggest things in the Universe, and even the structure of the Universe itself. However, new X-ray telescopes should be able to do even more. In fact, the hope is that X-ray astronomy will help us expand our understanding of physics itself.

My favorite topic here is neutron stars, collapsed dead stars that have the highest densities in the Universe. Lead has nothing on neutron stars. The whole Earth compressed to the density of a neutron star would be only about the size of three football fields. There's no way that we can replicate their conditions on Earth, so the only way to probe conditions in these super-densities is to study them in their natural laboratories in space. We plan on using X-ray telescopes to make detailed profiles of these extremely exotic objects. Once we have these, we can see if, for example, the density makes so-called 'strange quarks' come out into the open in these stars, as some have predicted, or if the cores become superfluids with no viscosity, or something else. It's quite important for us to know if this is the case, because, for example, if strange quarks become stable at the center of a neutron star then we might be able to find them elsewhere as well.

These are just a few of the topics that scientists hope X-ray astronomy will address in the coming years. As Chandra has shown, X-rays reveal something important in nearly every aspect of astronomy and astrophysics. In fact, the past 10 years with Chandra have shown that modern astrophysics needs a variety of telescopes to truly tackle the biggest problems. X-rays have been, and will continue to be, a vital player in our quest to explore the Universe.

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