A schematic diagram of velocity measurements of a rotating disk of hot gas in the core of active galaxy M87.

The measurement was made by studying how the light from the disk is redshifted and blueshifted -- as part of the swirling disk spins in earth's direction and the other side spins away from earth.

Credit: Holland Ford, Space Telescope Science Institute/Johns Hopkins University; Richard Harms, Applied Research Corp.; Zlatan Tsvetanov, Arthur Davidsen, and Gerard Kriss at Johns Hopkins; Ralph Bohlin and GeorgeHartig at Space Telescope Science Institute; Linda Dressel and Ajay K.Kochhar at Applied Research Corp. in Landover, Md.; and Bruce Margon fromthe University of Washington in Seattle NASA/ESA