Optical-to-Ultraviolet Spectrum of Markarian 231
This simplified spectral plot shows the radiation emitted from the center of a nearby galaxy that hosts a quasar. Visible and infrared light coming from a disk surrounding a central black hole in the middle of the galaxy is measured. Surprisingly, ultraviolet light from the disk, as measured by the Hubble Space Telescope, shows a drop in radiation from the disk. This is evidence for a large gap in the center of the disk that is likely carved out by a second black hole orbiting the primary black hole.
