The real monster black hole is revealed in this new image from NASA's Nuclear Spectroscopic Telescope Array of colliding galaxies Arp 299. This image shows the NuSTAR data alone.
Before NuSTAR, astronomers knew that the each of the two galaxies in Arp 299 held a supermassive black hole at its heart, but they weren't sure if one or both were actively chomping on gas in a process called accretion. The new high-energy X-ray data reveal that the supermassive black hole in the galaxy on the right is indeed the hungry one, releasing energetic X-rays as it consumes gas.
In this image, X-rays with energies of 4 to 6 kiloelectron volts are red, energies of 6 to 12 kiloelectron volts are green, and 12 to 25 kiloelectron volts are blue.