Dr. Fiona Harrison waited 20 years to see her X-ray telescope design launch into space.
If you happen to be on the lookout for black holes these days, you need to learn to operate on a budget. Just ask Dr. Fiona Harrison. She proposed a concept for a new kind of X-ray telescope about 20 years ago, and the device only made it into space last June. (Follow the mission at nasa.gov/nustar) The telescope, called NuSTAR, can make images 10 times sharper and register energies at a sensitivity 100 times that of previous X-ray telescopes such as NASA’s Chandra and the European Space Agency’s XMM-Newton. It’s already examined Cygnus X-1, the nearest black hole to earth (still 6,100 light years away), checked out remnants of supernovae in other galaxies, and will soon examine the center of our own galaxy, which — like all galaxies, apparently — houses a massive black hole of its own.
Harrison is a professor of physics and astronomy at the California Institute of Technology and only the second female project leader at NASA. “I was always interested in science and engineering because my father was a scientist,” she says, “but I never imagined majoring in physics when I was an undergraduate. I was thinking of more practical things, and I just had a fantastic physics teacher who taught me amazing things about the way physics and the universe works that are really strange and weird. When I was in graduate school, I planned on doing something sort of applied but then I heard about someone who was studying black holes and I just thought, ‘Wow, that’s really interesting,’ and I did a summer research project with him and got hooked.” Harrison put in the first proposal for what would become NuSTAR in 1995. “When we started there were no detectors or optics that could be used for focusing these high-energy X-rays, and we needed to develop optics with very smooth surfaces and new kinds of reflective coatings that are very demanding to make. We had to first figure out how we could form the optics, what kind of smooth substrates could we use that would be inexpensive enough because we needed many of them. The coatings are hundreds of layers of thin films — the thinnest ones are only a few atoms thick, and we have to put them down in a way that would make these very thin films.”
“When we’re looking at a black hole, we’re not actually seeing the black hole itself because light can’t escape it.”
NuSTAR is the first high-energy focusing telescope. Harrison explains, “Unlike any previous high-energy telescope, it concentrates and focuses the light from a source using optics onto an image — previous telescopes have worked more like a pinhole camera. X-rays only reflect at very glancing angles, which means the reflectors have to be almost parallel to the incoming beam. And if you think about that, if you have a reflector that’s almost parallel to the incoming light you’re not going to intercept very much. So we nest very many reflectors like Russian dolls so that you can intercept enough X-ray light. So the challenge for NuSTAR was both that the angle to reflect that gets smaller and smaller as the energy gets higher, so we needed many more, closely nested, very thin optics — so, by comparison, Chandra has four of these nested shells that are about a centimeter thick, and NuSTAR has 133 that are just the thickness of your fingernail. In addition to that, we have to have these special reflective coatings that are kind of like the antireflective coatings on your glasses, only they’re designed to enhance reflection. We have to coat these substrates once we have them because they’re glass, and we coat them in this custom chamber, and we needed a new kind of digital camera because the digital camera used in previous missions wouldn’t stop these high-energy X-rays.”The NuSTAR mission is led by Caltech, managed by JPL for NASA, while the spacecraft itself was built by Orbital Sciences Corporation in Dulles, Virginia. Instead of being launched from an old-school gantry rocket, NuSTAR was slung underneath a specially equipped L-1011 airliner in a very long rocket that would drop from the plane and then boost the device into earth’s orbit. In its second year of operation, NuSTAR is set to examine Earth’s sun in order to determine how the star’s outer region, or heliosphere, remains hotter than the interior of the star.
Harrison’s study of black holes have exposed her to a lot of misconceptions about the mysterious objects: “One of the questions I often get asked is, ‘Won’t a black hole suck up all the matter in a galaxy eventually?’ That’s a big misconception because really black holes aren’t sucking, they just have gravity — like stars and planets have gravity — and the sphere of influence of a black hole, which means the distance to which its gravity is stronger and more influential than the stars in a galaxy, is not very large. The other misconception is when we’re looking at a black hole, we’re not actually seeing the black hole itself because light can’t escape it — what we’re seeing is all the matter around the black hole that’s falling onto it and even heating up and radiating, lighting up.”
One thing she apparently hadn’t been asked before is what happens if you fall into one? “You’d have to think about how close you’d be before the strong difference in gravity between your head and your feet started to affect you biologically,” she replies. In other words, you might get stretched like a rubber band. Yikes.