... and the black hole that ate too much.
A black hole in the galaxy M83 might have bitten more off than it should be able to chew. Black holes theoretically adhere to the Eddington limit, which predicts that an accreting black hole can only spew so much energy in jets, winds, and radiation from its fluffy disk. Above the limit, all that outward-pushing radiation cuts off the flow of infalling gas and starves the beast.
Black holes occasionally violate this limit, but only for short periods of time. But as Roberto Soria (Curtin University, Australia) and colleagues report February 27th in Science, one black hole looks like it broke its limit for roughly 20,000 years.
The team studied the binary system MQ1 in X-rays, optical, infrared, and radio. The X-rays come from the black hole's accretion disk, and based on how the disk's emission should look for a given mass, the team used the system's X-ray brightness to estimate the black hole's mass.
The astronomers also studied a bubble around MQ1, ostensibly inflated by the black hole's jets and other outflows. Based on the emission from hot gas inside the bubble, they calculated how much energy was dumped into the gas and, therefore, the average jet power needed to do it.
Finally, they used the estimated jet power, the bubble's estimated size, and the gas's presumed density to calculate how long the structure had been expanding.
Put together, the evidence suggests that the black hole is between 10 and 115 solar masses, with a best guess of a little more than 40. Over 20,000 years, it ejected 1052 ergs in energy into its surroundings, 10 times more than a typical supernova would. If the black hole is about 40 solar masses, the energy output is a few times above its Eddington limit.
Joey Neilsen (Boston University) says the biggest puzzle is why the black hole appears to have broken the Eddington limit for so long. Stellar-mass black holes in binary systems often "turn on" for several months or a year, spitting out jets, and then they fade away for a decade or more.
Soria says it should be possible for a black hole to go three to four times above its Eddington rate for up to 100,000 years if a massive companion star dumps a huge amount of dense, opaque gas onto the black hole. Normally, the pressure of photons produced inside the infalling gas can build up so much that it can shut off the infall. But if the gas is very dense and opaque to radiation, the photons' escape is delayed--sometimes they can't even emerge before the gas surrounding them crosses the black hole's event horizon. In this case, the photons can't "do their duty of pushing gas away," he says. He suspects that's what happened with MQ1.
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|Title Annotation:||News Notes|
|Author:||Carlisle, Camille M.|
|Publication:||Sky & Telescope|
|Date:||Jun 1, 2014|
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