June 19, 2012: Black holes in the early universe needed a few snacks rather than one giant meal to fuel their quasars and help them grow, a new study shows. Quasars are the brilliant beacons of light that are powered by black holes feasting on captured material, and in the process, heating some of the matter to millions of degrees. The brightest quasars reside in galaxies distorted by collisions with other galaxies. These encounters send lots of gas and dust into the gravitational whirlpool of hungry black holes. Now, however, astronomers are uncovering an underlying population of fainter quasars that thrive in normal-looking spiral galaxies. They are triggered by black holes snacking on such tasty treats as a batch of gas or the occasional small satellite galaxy.
A census of 30 quasar host galaxies conducted with two of NASA's premier observatories, the Hubble Space Telescope and Spitzer Space Telescope, has found that 26 of the host galaxies bear no tell-tale signs of collisions with neighbors, such as distorted shapes. Only one galaxy in the sample shows evidence of an interaction with another galaxy. The galaxies existed roughly 8 billion to 12 billion years ago, during a peak epoch of black-hole growth. The study bolsters evidence that the growth of most massive black holes in the early universe was fueled by small, long-term events rather than dramatic short-term major mergers.See the rest: