- Supermassive black holes at the centers of galaxies
- Do supermassive black holes regulate galaxy evolution?


[SLIDE 1]

A small percentage of galaxies, known as active galaxies, emit extreme amounts of radiation from their central regions. The central region of such a galaxy is known as an active galactic nucleus. The most luminous examples of such galactic nuclei are known as quasars, and can be more than a trillion times more luminous than our Sun.

Scientists believe that these active galaxies contain supermassive black holes, usually no bigger than our solar system. This black hole is probably surrounded by a swirling accretion disk of very hot gas, similar to what we see in X-ray binary star systems. Matter falling into these supermassive black holes is converted into the radiation we see from billions of light years away.

Evidence for black holes is based on looking at the orbits of objects around the centers of such galaxies. Based on the characteristics of these orbits, scientists have calculated that the mass of the relatively small objects in the centers of these galaxies must be billions of times greater than our Sun. The only object known to pack so much mass into so small a space is a black hole.

Evidence collected during the last two decades indicates that it is possible that ALL galaxies have a supermassive black hole at their centers.


[SLIDE 2]

Studies have revealed that the size of a galaxy's bulge is related to the mass of its central black hole. In other words, galaxies with large bulges have large black holes, while those with smaller bulges have smaller black holes.

This may indicate that black holes play a part in a galaxy's evolution. The study of radio galaxies, which are galaxies with unusually strong radio-wave emissions, reveals that active galactic nuclei can release powerful jets of matter that heat the surrounding gas. By heating the gas, the central black holes can delay or prevent the formation of new stars.