NewScientist.com news service
David Shiga
Just how big can a black hole grow? Two astronomers reckon they have worked out the answer: colossal black holes with a mass of up to 50 billion suns could be lurking out there – but that's the limit.
Giant black holes sit at the cores of virtually all galaxies, and are thought to have grown from smaller seed black holes that swallowed lots of matter. The biggest well-measured one resides in the galaxy Messier 87 and has the mass of 3 billion suns, a measurement based on the speed of the gas swirling around it.
Even bigger black holes are waiting to be found, say Priya Natarajan of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and Ezequiel Treister of the European Southern Observatory in Santiago, Chile.
In a study to appear in Monthly Notices of the Royal Astronomical Society, the pair examined the "feeding habits" and growth of black holes. They used data from surveys carried out by other teams that observed the X-rays and visible light emitted by matter as it is devoured by black holes. The properties of this radiation can be used to estimate a black hole’s mass and how quickly it is gobbling up its surroundings.
The team analysed how many galactic black holes of various masses were present at each stage in the universe's history. The distribution of masses they found today and in the past can only be explained if there is a limit on how fast black holes can grow, the researchers say.
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http://space.newscientist.com/article/dn14653-how-big-can-a-black-hole-grow.html
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