Tuesday, March 5, 2013

Study Sheds New Light on Black Hole Growth

Study Sheds New Light on Black Hole Growth

A study from Melbourne's Swinburne University of Technology has turned up surprising results that have shattered theories about the size and growth of black holes.

Dr. Nicholas Scott and Professor Alister Graham discovered that the central black holes of smaller galaxies do not correspond to the ratios seen in larger galaxies. Scott and Graham created a database of 77 galaxies, then determined the mass of their central black holes by recording the speed of stars orbiting around them.

The prevailing theories predicted that the growth of black holes would correspond directly with the growth of the galaxies in which they reside. This paper, which will be published in the Astrophysical Journal, showed that central black holes saw a hundredfold mass increase for each tenfold mass increase seen in the host galaxies.

The growth of black holes is spurred by galactic mergers. Smaller galaxies contain dense star clusters near the center that make up a higher percentage of total mass than seen in larger galaxies. Thus, when they merge, the greater density of material near the center allows the central black hole to quadruple in size.

The prevailing theory about black hole growth also did not account for so-called intermediate mass black holes. Scientists have long searched for these missing black holes, at a mass somewhere in between the supermassive black holes in galactic centers and the stellar mass black holes left behind in the wake of a giant star's death. These findings account for the intermediate sizes, which are between ten thousand and a hundred thousand times the Solar mass, and Alister Graham believes "we've found several good candidates."

With the advent of large, higher-powered telescope in our near future, these surprising results may be directly observed and studied in greater detail.

Image credit: SPL / Artists' Conception of a supermassive black hole.

Sources: http://www.sciencealert.com.au/news/20131701-23970-2.html

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