Q: What’s “new” about NuSTAR?
NuSTAR is the first focusing high-energy X-ray telescope. X-rays can be focused by reflection, but they’re so penetrating that they only reflect at very glancing angles—sort of like skipping a stone off the surface of a lake. But most of the X-rays don’t interact even then, so you use “nested optics,” which you can think of as a set of cones nested inside one another like Russian dolls. Each cone intercepts some of the X-ray beam. The higher the energy, the more glancing the reflecting angle is, and the more cones you need.
Other focusing telescopes, such as NASA’s Chandra X-ray Observatory and the European Space Agency’s X-ray Multi-Mirror Mission, observe X-rays with energies below about 10 kilo-electronvolts. NuSTAR can see up to 79 kilo-electronvolts. Chandra has four nested mirrors, each about an inch thick and set at about a one-degree angle; NuSTAR has 133 mirrors as thin as my fingernail and almost parallel to the incoming light. We developed the detector here at Caltech. It’s a digital camera, but made out of a special material that stops the high-energy X-rays that would have gone straight through previous X-ray imaging detectors.
Read more at: Phys.org