Figure 13-68 Supermassive Black Holes as Engines for Galactic Activity (a) Analogous to the activity depicted in Figure 12-46, in the accretion disk around a supermassive black hole, inswirling gas heats and expands. Pulled inward, compressed, and heated further, some of it is eventually expelled perpendicular to the disk in two jets. (b) The giant elliptical galaxy NGC 4261 is a double-radio source located in the Virgo cluster, about 100 million ly from Earth. An optical photograph of the galaxy (white) is combined with a radio image (orange and yellow) to show both the visible galaxy, which does not emit much radio energy, and its jets, which do. Inset: This Hubble Space Telescope image of the nucleus of NGC 4261 shows a disk of gas and dust about 800 ly (250 pc) in diameter, orbiting a supermassive black hole.