NuSTAR is the NASA space telescope launched in 2012 to observe high-energy X-rays from black holes and other cosmic sources.
NuSTAR stands for Nuclear Spectroscopic Telescope Array. It focuses hard X-rays in the approximate 3–79 keV energy range, allowing astronomers to study energetic regions that are difficult or impossible to observe with ordinary optical telescopes. Its targets include black-hole accretion disks, hot coronae, supernova remnants, and active galaxies.
The observatory launched on 13 June 2012 aboard a Pegasus XL rocket from Kwajalein Atoll. A long deployable mast separated its grazing-incidence optics from the detectors, giving the telescope the focal length needed to produce focused hard-X-ray images.
NuSTAR does not photograph a black hole’s event horizon directly. Instead, it measures X-rays from superheated matter around the black hole and can investigate effects such as relativistic reflection and the spin of the central object. GALEX observed ultraviolet light, Kepler searched for planetary transits, and Spitzer operated primarily in infrared wavelengths.