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Black Holes Can Over-Eat, Too.

Black Holes Can Over-Eat, Too.

Black holes cannot accrete more than 50 billion suns-worth of mass, according to new find.

Once upon a time, it was thought that black holes could ‘eat-up’ accreted matter. That is: gas, dust, and other such things that have been pulled into the black hole’s gravity field, usually forming a disk of rotating material. The black holes would pull the matter into infinity, with no limit to how large a black hole could become in this manner.

However, Andrew King, from Leicester University, has recently determined with rock-solid mathematics that black holes cannot grow beyond the 50 billion-sun mark before the very accretion disk that they rely on for ‘food’ becomes unstable and collapses away – leaving the affected black hole with no more matter from which to grow.

Now, this doesn’t mean that black holes can’t actually grow to mass-sizes greater than 50 billion suns – it can always do so by coming upon a star and consuming that, or by merging with another black hole.  However, mathematically, it cannot accrete (pull into a disk about itself) material beyond this particular limit.

The black hole at the center of our own Milky Way galaxy is a mere 3.3 million suns – tiny compared to some of the very largest ones ever found, inhabiting the centers of the largest, elliptical galaxies and possessing around 40 billion suns-worth of mass.

But these are just the ‘supermassive’ black holes that reside at galactic centers; most black holes are ‘stellar’-sized, only a few dozen times more massive than our Sun, and will most likely not grow much larger.  However, somewhere out in the Universe, there is likely to be a black hole, or two or more, whose accretion limit has been reached and so at this time has been ‘starved’ of matter to become any larger.

References:
Andrew King (2015). How Big Can a Black Hole Grow? MNRAS Letters arXiv: 1511.08502v2
Rt.com 

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Jeffrey Daniels
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