The Secrets of Black Holes: Meet NuSTAR, NASA's New X-Ray Mission
The new space telescope is going to look at black holes and the power they have over the objects around them.
In just an hour, NASA will launch a new spacecraft, NuSTAR, into orbit around the Earth. From its perch in orbit over the equator, NuSTAR will be collecting data on high-energy X-rays, helping us to better understand the physics of black holes and the effects they have on the space around them. The first images should start beaming down to Earth through a space center in Malindi, Kenya, in just ten days.
Yesterday, I spoke with Fiona Harrison, the mission's principal investigator, about what she hopes NuSTAR will achieve, and what it feels like to be on the cusp of sending the product of more than a decade's work off into space.
Why don't we begin with you telling me about the genesis of the mission and how you first got interested in black holes.
Harrison: I really didn't think of becoming an astrophysicist until I was in graduate school. I went to graduate school in physics at Berkeley and started thinking I would do something very practical like solid-state physics where you're developing materials for electronics devices and things like that. I started doing research and it just didn't capture me.
There was a faculty member at Berkeley at the time building an instrument to study black holes that's now on a European satellite and just something about it was so intriguing. I just got hooked on the whole idea of understanding these exotic and interesting phenomenon in the universe. For my dissertation I built an X-ray telescope for a balloon experiment and realized that the sensitivity -- the clarity of the images it could make, the sorts of objects it could study -- was really limited.
I went to CalTech and started working with a team of people to develop a new kind of focusing, high-energy telescope -- a telescope that could go much deeper and make much better images of the cosmos.
When did that work evolve into the NuSTAR mission?
Harrison: We developed the technologies starting about 15 years ago but it wasn't until six years ago that we really in earnest started developing NuSTAR as a space mission.
Can you talk about how this will compare with NASA's Chandra Space Telescope and other ways that we have studied X-rays in the universe?
Harrison: Sure. If we think of the X-ray spectrum as broken up into low-energy X-rays and high-energy X-rays, the Chandra observatory and other sensitive telescopes like ESA's XMN-Newton, they have observed the universe in low-energy X-rays. NuSTAR is going to be the first telescope to make sensitive images in the high-energy X-ray band. High-energy X-rays are those used by a doctor or a dentist to penetrate through your skin and image your teeth or your bones. They are very penetrating; they can penetrate through a lot of dust and gas [in space]. So we will be able to see objects that are hidden from view at low-energy X-ray wavelengths or optical (visible) light. Also we will be able to study regions where particles are accelerated very close to the speed of light, very hot regions, very close to black holes. So all of these are uniquely studied in the high-energy X-ray band.
One of the things I'm really excited about is that by partnering with Chandra and XMN-Newton and looking at the same objects at the same time, we can cover the entire X-ray spectrum and get information that otherwise we couldn't access with just one telescope alone.
What are some of the regions of space, or particular objects, that you're looking forward to seeing and why?
Harrison: For me, the study of black holes and other what we call compact objects is the most exciting. The black holes themselves don't emit light; no light can escape from within the event horizon. But black holes don't live in isolation -- they live in galaxies where there's dust and gas and their gravity attracts the dust and gas. As they fall on to the black hole, friction heats them up until it gets very hot. The innermost regions near the black hole -- just a few times the size of the event horizon -- emit very strongly in the high-energy X-ray band. In these regions, particles are accelerated very close to the speed of light.
One of the things I'm really excited about is that by partnering with XMN-Newton and looking at these inner regions around black holes, we will actually be able to track the orbits of atoms just before they disappear forever and get eaten by the black hole, and see how those orbits are severely distorted by the strong gravity, by the warping in space-time. So usually when the materials fall on, it organizes itself into a disc, we see that disc -- instead of looking like a pancake -- it's all sort of folded back on itself and we see these trajectories as severely distorted. By looking at this we can measure, for example, how fast the black hole is spinning.
Another thing is that we used to think that black holes were exotic and rare but we now know that every massive galaxy has a massive black hole at its heart. So these black holes -- once thought to be interesting but unimportant in determining how the cosmos is put together -- it turns out they influence the way galaxies and stars form, because they pump so much energy out into the galaxies.
And is there any black hole that stands out to you as particularly interesting?
Harrison: Unfortunately they don't have very captivating names, but the one system I'm looking forward to has the sexy name of MCG 6-30-15. It's postulated that it's spinning very fast. And if we can get the data to show us that that's true, it will tell us something about how these massive black holes grow.
How are you feeling on the eve of the launch? What has the run-up to the launch been like for you?
Harrison: Well it's just been ... the last few weeks, leading up to the launch, I've tried not to think about it too much, because otherwise you just lie awake at night worrying. It is kind of like sending your kid off to school for the first time or to college. But it's incredible. There's no feeling like it. We've worked so hard and the team has worked so hard and done such a great job. And it's about to become a reality. We're about to get these great images and open this new window on the universe. It's amazing.
This interview has been condensed and edited for clarity.