Supernova remnant Cassiopeia A as viewed by NuSTAR
Cassiopeia A is the remnant of a star that blew up in a supernova event whose light reached Earth about 350 years ago, when it could have appeared to observers as a star that suddenly brightened. The remnant is located 11,000 light-years away from Earth. In this image, NuSTAR data, which show high-energy X-rays from radioactive material, are colored blue. Lower-energy X-rays from non-radioactive material, imaged previously with NASA's Chandra X-ray Observatory, are shown in red, yellow and green. The red, yellow and green data were collected by Chandra at energies ranging from 1 to 7 kiloelectron volts (keV). The red color shows heated iron, and green represents heated silicon and magnesium. The yellow is what astronomers call continuum emission, and represents a range of X-ray energies. The titanium-44, shown in blue, was detected by NuSTAR at energies ranging between 68 and 78 keV.