An active galactic nucleus (AGN) is the center of a galaxy that has a supermassive black hole being fed by gas and dust near it. At one time, such AGN’s were called quasars, which is short for quasi-stellar radio source. Also at one time, our own Milky Way galaxy may have had an AGN, until its central black hole consumed all the gas and dust near it.
However, an alternative theory is that an AGN comes from the merger of two galaxies. So which theory is correct? That is what the Hubble Space Telescope set out to prove.
Most galaxies, including our own, have a huge but well-behaved black hole at their heart, while some have messy eaters that suck in vast amounts of matter which then shines brightly as it falls towards oblivion. This causes the telltale bright spots at the centre of galaxies known as active galactic nuclei (AGN). Why are the two types so different? Until now, the leading theory has been that mergers between galaxies are instrumental in driving matter into the black holes, making them grow.
In a new study, the largest of its kind so far, astronomers set up an identity parade of galaxies to test this theory. Comparing 140 active galaxies with a control group of over 1200 comparable inactive galaxies, they found that there has been no significant link between AGN activity and galactic mergers for at least the past eight billion years. Therefore, other phenomena such as instabilities within galaxies, collisions of molecular clouds or tidal disruption by other galaxies flying by must instead be to blame.
via : Identity Parade Clears Cosmic Collisions of the Suspicion of Promoting Black Hole Growth
Video after the break:
