NASA spots giant black hole rejecting food

Astronomers at the Chandra X-ray Observatory explain why the black hole at the heart of the Milky Way galaxy doesn't consume everything in sight.

The center of the Milky Way galaxy with the black hole Sagittarius A* located in the middle. IR: NASA/STScI,X-ray: NASA/UMass/D.Wang et al.
You might think of black holes as voracious eaters that suck up everything in sight. But astronomers using NASA's Chandra X-ray Observatory have found that the black hole at the heart of the Milky Way galaxy is actually quite sloppy when it comes to its culinary habits.

New images of Sagittarius A*, or Sgr A* (pronounced "Sagittarius A-star"), which is approximately 26,000 light-years from Earth, reveal that the black hole manages to suck up less than 1 percent of the gas within its reach. Instead, most of it is tossed back out into space before it's ever devoured.

"Contrary to what some people think, black holes do not actually devour everything that's pulled towards them," Feng Yuan of Shanghai Astronomical Observatory in China wrote in a study about the findings. "Sgr A* is apparently finding much of its food hard to swallow."

This answers a mystery that has been confounding astronomers for some time -- why some black holes appear to be surprisingly dim. Black holes form when massive stars die and the gravity is so strong that not even light can escape. The gravitational force of black holes can be measured by X-ray emissions, which indicate how much heat is generated.

"There's been a debate for the last 20 years or so about what actually is happening to the matter around the black hole," said research leader Q. Daniel Wang of the University of Massachusetts, Amherst. "Whether the black hole is accreting the matter, or actually whether the matter can be ejected. This is the first direct evidence for outlflow in the accretion process."

The findings are the result of one of Chandra's longest observation campaigns ever. The spacecraft collected five weeks' worth of data on Sgr A* last year, during which time, researchers captured detailed X-ray images of super-heated gas swirling around the black hole.

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