Researchers See Brightest Flare Ever in Milky Way’s Black Hole

Wed, 11/07/2012 - 12:12pm
MIT, Jennifer Chu

This false-color image shows the central region of our Milky Way Galaxy as seen by Chandra. The bright, point-like source at the center of the image was produced by a huge X-ray flare that occurred in the vicinity of the supermassive black hole at the center of our galaxy. Image: NASA, MIT, F. Baganoff et al.As black holes go, Sagittarius A* is relatively low-key. The black hole at the center of our galaxy emits very little energy for its size, giving off roughly as much energy as the sun, even though it is 4 million times as massive.


Now a team of scientists from MIT, the Univ. of Amsterdam, the Univ. of Michigan and elsewhere have used NASA’s Chandra X-Ray Observatory to detect the brightest flare ever observed from Sagittarius A*. The flare, recorded from 26,000 light years away, is 150 times brighter than the black hole's normal X-ray luminosity. Scientists observed the flare for more than one hour before it faded away. This brief burst of activity, they say, may be a clue to how mature black holes like Sagittarius A* behave.

“We’re learning what black holes do when they’re old,” says Joey Neilsen, a postdoc at MIT’s Kavli Institute for Astrophysics and Space Research. “They’re no young whippersnappers like quasars, but they’re still active, and how they’re active is an interesting question.”

Neilsen and his colleagues published their results recently in The Astrophysical Journal.

A finicky eater


“Everyone has this picture of black holes as vacuum sweepers, that they suck up absolutely everything,” says Frederick Baganoff, a research scientist at MIT Kavli. “But in this really low-accretion-rate state, they’re really finicky eaters, and for some reason they actually blow away most of the mass available for them to consume.”

To detect such a faint signal, the team reserved observing time on NASA’s Chandra X-Ray Observatory, a giant space-based telescope designed to detect extremely faint objects. The team obtained images of the black hole from Chandra, and utilized the telescope’s High Energy Transmission Gratings Spectrometer (HETGS), an instrument built by MIT physics professor Claude Canizares (now the Institute’s vice president for research and associate provost), to analyze the incoming light.

The onboard spectrometer split the black hole’s X-rays into various wavelengths, much like light passed through a prism. The researchers analyzed the data, and found a spike of 700 photons — which, while small compared with more active galaxies, was 150 times brighter than the black hole’s normal luminosity. 

“Suddenly, for whatever reason, Sagittarius A* is eating a lot more,” says Michael Nowak, a research scientist at MIT Kavli. “One theory is that every so often, an asteroid gets close to the black hole, the black hole stretches and rips it to pieces, and eats the material and turns it into radiation, so you see these big flares.”

The great escape


Mark Morris, a professor of astronomy at the Univ. of California at Los Angeles, says that while less luminous flares occur daily, scientists have detected very few events from the black hole as bright as this recent flare-up.



“We’re really studying the great escape, because most of the gas escapes, and that’s not what we expect,” Baganoff says. “So we’re piecing out the history of the activity of the center of our galaxy.”



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