Black Holes in Other Galaxies

1. Black Holes in Other Galaxies

2. Black Holes in Other Galaxies The giant elliptical galaxy M87 is located 50 million light-years away in the constellation Virgo.

3. Black Holes in Other Galaxies Evidence for a Supermassive Black Hole in M87 The observations indicate that approximately 3 billion solar masses are concentrated in a region at the galactic core that is only about the size of the Solar System.

4. Black Holes in Other Galaxies Compelling Evidence The following figure illustrates observations taken with the Hubble Space Telescope Imaging Spectrograph of a region across the center of the galaxy M84, which is in the Virgo Cluster about 50 million light years away. The right portion of the figure is a radial velocity distribution across the slice illustrated in the left portion of the figure, determined by looking at the Doppler shift of light coming from this region. As one approaches the nucleus (moving downward in the right image) there is a sudden blue shift, indicating rapid motion of the gas near the nucleus toward us. The Doppler shift indicates that the velocity toward us reaches as high as 400 km/s at a distance only 26 light years from the center. Then suddenly the sign of the radial velocity reverses and a redshift indicating similar velocities away from us is observed, with this red shift decreasing rapidly as one moves away from the center (toward the bottom of the right diagram). The most obvious interpretation of these data is that there is a large rotating disk around the nucleus of M84 that we are seeing in cross section. Above the nucleus in this image the disk matter is moving toward us at 400 km/s, and below the nucleus the disk matter is moving away at similar velocities. The only simple explanation is that this is an accretion disk feeding a supermassive black hole in the center of M84, since no other explanation could easily account for gas velocities of these magnitudes near the center. Thus, we may take the "S" shape of such velocity distributions for galactic cores as telltale signs for an accretion disk around a supermassive black hole. This black hole interpretation is strengthened by previously known information about this galaxy: its nucleus very active and emits jets of particles that are very strong radio sources. The observed radial velocities near the center suggest a mass of about 300 million solar masses for the black hole.

5. Black Holes in Other Galaxies Evidence for a Supermassive Black Hole in NGC4261 The image shows a composite of ground based optical and radio telescope images of the galaxy NGC 4261, and a high resolution Hubble Space Telescope image of the core of this galaxy. NGC 4261 has enormous jets shooting from its core and very strong radio frequency emission. It is thought that the jets are powered by a gargantuan black hole of perhaps a billion solar masses, and that the ring in the Hubble image is an accretion disk feeding the black hole. The black hole itself presumably lies inside the bright spot at the center. Even a billion solar mass black hole would be too small to see in this image

6. Black Holes in Other Galaxies The image is of the Sombrero Galaxy (M104). This galaxy is a strong X-Ray emitter, and unusually high velocities are observed for stars near its center; this raises speculation that it may have a black hole of approximately 1 billion solar masses at its core. Credit: T. Boroson (NOAO /USGP), W. Keel (UA), KPNO

7. Black Holes in Other Galaxies Origin of Supermassive Black Holes It is now believed that many galaxies have supermassive black holes at their centers, and that whether such galaxies are active galaxies is a question of whether mass is being fed into these black holes. The simplest ideas for the origin of such supermassive black holes are that they are conglomerations of many star-size black holes that were formed during the history of a galaxy, or perhaps that galaxies formed around large black holes that then grew by accreting matter.