Scientists explain obscene growth of black holes

Washington, March 25 (IANS) A new theory about why black holes become so hugely massive has been put forth by astronomers from University of Leicester, UK and Monash University, Australia.

Andrew King, professor of physics from Leicester, said: "Almost every galaxy has an enormously massive black hole in its centre," the journal Monthly Notices of the Royal Astronomical Society reported.

Our own galaxy, the Milky Way, has one about four million times heavier than the sun. "But some galaxies have black holes a thousand times heavier still. We know they grew very quickly after the Big Bang," said King.

"These hugely massive black holes were already full grown when the universe was very young, less than a tenth of its present age," added King, according to a university statement.

Black holes grow by sucking in gas. This forms a disc around the hole and spirals in, but usually so slowly that the holes could not have grown to these huge masses in the entire age of the universe.

"We needed a faster mechanism, so we wondered what would happen if gas came in from different directions," said Chris Nixon, also at Leicester.

Nixon, King and their colleague Daniel Price in Australia made a computer simulation of two gas discs orbiting a black hole at different angles. After a short time the discs spread and collide, and large amounts of gas fall into the hole. According to their calculations black holes can grow 1,000 times faster when this happens.

"If two guys ride motorbikes on a Wall of Death and they collide, they lose the centrifugal force holding them to the walls and fall," said King. The same thing happens to the gas in these discs, and it falls in towards the hole.

This may explain how these black holes got so big so fast. "We don't know exactly how gas flows inside galaxies in the early universe, but I think it is very promising that if the flows are chaotic it is very easy for the black hole to feed," said King.