A new study by a University of Leicester researcher claims that the black holes that reside in the hearts of galaxies can swell up to 50 billion times the mass of the sun before running out of the gas that they rely on to sustain themselves.
Black holes make their home in the centers of galaxies due to the fact that there are regions of space surrounding these areas where gas settles into an orbiting disc. This gas disc can subsequently lose energy and move inwards, feeding the black hole and acting as its "food source." However, when these discs crumble into stars due to instability, what happens to the black hole?
The study suggests that without a gas disc, the black hole would cease to grow, and the only way that it could continue to expand would be if a star fell directly into it or it merged with another black hole. Barring these situations, once a black hole reaches 50 billion times the mass of the sun, its outer edge would become be too large to enable the formation of a gas disc, making this its upper growth limit.
"The significance of this discovery is that astronomers have found black holes of almost the maximum mass, by observing the huge amount of radiation given off by the gas disc as it falls in," Andrew King, author of the study, said in a press release. "The mass limit means that this procedure should not turn up any masses much bigger than those we know, because there would not be a luminous disc.
"Bigger black hole masses are in principle possible - for example, a hole near the maximum mass could merge with another black hole, and the result would be bigger still. But no light would be produced in this merger, and the bigger merged black hole could not have a disc of gas that would make light."
The findings were published in the Dec. 17 issue of the journal Monthly Notices Letters of the Royal Astronomical Society.
