CASPER
New member
he center of most galaxies harbors a massive black hole. So does our Milky Way. The exotic object there, however, is calm, unlike some supermassive gravity monsters in other galaxies. Scientists at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, and other institutions around the world have analyzed 199 of these galaxies and discovered what makes black holes at galaxy centers become active — black holes switched on some 700 million years ago after major galaxy merger events.
While in our own galaxy the central black hole was measured to have about 4 million solar masses, the 199 galaxies analyzed host black holes with a typical mass of about 300 million solar masses. These galaxies are larger than our Milky Way and also active, which means that the inner region of the galaxy has a higher luminosity than normal.
Astronomers believe this radiation is powered by the accretion of matter on the supermassive black hole. Previous studies suggest that the formation and evolution of the host galaxies and their black holes are closely connected. However, there are various possibilities how the interstellar gas can be funneled toward the black hole, and it is unclear which of these mechanisms is dominant at what stage in the evolution of a galaxy.
The two main mechanisms discussed are either internal disruptions, such as galaxy disk instabilities, or mergers and tidal interactions between close pairs of galaxies. Simulations of these scenarios lead to different predictions about the clustering of active galaxies and the masses of the host galaxies. Previous studies have analyzed active galaxies selected by their optical or soft X-ray emission, which misses a major part of the radiation powered by the black hole accretion due to absorption and other effects.