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Milky Way's Black Hole Shows Signs of Increased Chatter

For Release: September 23, 2015


Credit: NASA/CXC/MPE/G.Ponti et al; Illustration: NASA/CXC/M.Weiss
Press Image and Caption

Three orbiting X-ray space telescopes have detected an increased rate of X-ray flares from the usually quiet giant black hole at the center of our Milky Way galaxy after new long-term monitoring. Scientists are trying to learn whether this is normal behavior that was unnoticed due to limited monitoring, or these flares are triggered by the recent close passage of a mysterious, dusty object.

By combining information from long monitoring campaigns by NASA's Chandra X-ray Observatory and ESA’s XMM-Newton, with observations by the Swift satellite, astronomers were able to carefully trace the activity of the Milky Way’s supermassive black hole over the last 15 years. The supermassive black hole, a.k.a. Sagittarius A*, weighs in at slightly more than 4 million times the mass of the Sun. X-rays are produced by hot gas flowing toward the black hole.

The new study reveals that Sagittarius A* (Sgr A* for short) has been producing one bright X-ray flare about every ten days. However, within the past year, there has been a ten-fold increase in the rate of bright flares from Sgr A*, at about one every day. This increase happened soon after the close approach to Sgr A* by a mysterious object called G2.

"For several years, we've been tracking the X-ray emission from Sgr A*. This includes also the close passage of this dusty object” said Gabriele Ponti of the Max Planck Institute for Extraterrestrial Physics in Germany. “A year or so ago, we thought it had absolutely no effect on Sgr A*, but our new data raise the possibility that that might not be the case."

Originally, astronomers thought G2 was an extended cloud of gas and dust. However, after passing close to Sgr A* in late 2013, its appearance did not change much, apart from being slightly stretched by the gravity of the black hole. This led to new theories that G2 was not simply a gas cloud, but instead a star swathed in an extended dusty cocoon.

"There isn't universal agreement on what G2 is," said Mark Morris of the University of California at Los Angeles. "However, the fact that Sgr A* became more active not long after G2 passed by suggests that the matter coming off of G2 might have caused an increase in the black hole’s feeding rate."

While the timing of G2’s passage with the surge in X-rays from Sgr A* is intriguing astronomers see other black holes that seem to behave like Sgr A*. Therefore, it’s possible this increased chatter from Sgr A* may be a common trait among black holes and unrelated to G2. For example, the increased X-ray activity could be due to a change in the strength of winds from nearby massive stars that are feeding material to the black hole.

"It's too soon to say for sure, but we will be keeping X-ray eyes on Sgr A* in the coming months," said co-author Barbara De Marco, also of Max Planck. "Hopefully, new observations will tell us whether G2 is responsible for the changed behavior or if the new flaring is just part of how the black hole behaves."

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The analysis included 150 Chandra and XMM-Newton observations pointed at the center of the Milky Way over the last 15 years, extending from September 1999 to November 2014. An increase in the rate and brightness of bright flares from Sgr A* occurred after mid-2014, several months after the closest approach of G2 to the huge black hole.

If the G2 explanation is correct, the spike in bright X-ray flares would be the first sign of excess material falling onto the black hole because of the cloud’s close passage. Some gas would likely have been stripped off the cloud, and captured by the gravity of Sgr A*. It then could have started interacting with hot material flowing towards the black hole, funneling more gas toward the black hole that could later be consumed by Sgr A*.

A paper on these findings has been accepted by the Monthly Notices of the Royal Astronomical Society. A preprint is available online. NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.

An interactive image, a podcast, and a video about the findings are available at:

For more Chandra images, multimedia and related materials, visit:

Media contacts:
Megan Watzke
Chandra X-ray Center, Cambridge, Mass.

Visitor Comments (14)

The article by Ponti et al reached publication status in July 2015. What's curious is that time dilation prevents anything ever being seen by outsiders to cross the event horizon of a black hole. We're also led to wonder whether Sagittarius A will eat the rest of the Milky Way given enough time.

Posted by jesse baker on Sunday, 01.24.16 @ 19:30pm

In addition, we have a big problem, which is called sensitivity in measuring devices... what if, in the future, we advance the sensitivity of the measurement system, and we measure some energy coming from a black hole? How much of the theoretical models would be destroyed? This question is consistent with what would happen if in the future we measure that the speed of light is not constant, and varies throughout the universe?

Posted by cristian meys on Sunday, 01.24.16 @ 08:04am

I do not think black holes, as many understand them, exist. I think we do not yet know clearly the essential laws of physics, and we base, almost dogmatically, in some theoretical models, which only partially explain something of the nature we study.

Posted by cristian meys on Sunday, 01.24.16 @ 08:03am

Isn't Sagittarius our home galaxy?

Posted by Anna Calcagno on Wednesday, 01.6.16 @ 05:46am

These images are amazing and naturally creates so many questions in mind.

Posted by pawar anil on Sunday, 12.27.15 @ 10:15am

What if the Universe continually produce black holes? Will the universe collapses? This seem to be what the Big bang evolved from. Theoretically speaking.

Posted by LEONARD JACKSON on Monday, 11.30.15 @ 22:05pm

Oppenhiemer and Wheeler used to argue over the nature of Black Hole physics and not much else has been added to this discussion except astronomical observations. Perhaps, some real imagination is required to think the impossible and I not talking the current paradigm nor wormholes in space. Black holes will be part of the natural evolution of energy and not bound by the state of our scientific understanding at this moment it time.

Posted by trevor on Sunday, 11.22.15 @ 17:36pm

How many black holes have been identified found in our galaxy?

Posted by Balaji Kartha on Sunday, 10.18.15 @ 00:54am

As of now there is no BLACK HOLE near to earth. Hunt for black hole requires very powerful telescopes. Another way to detect these objects are by gravitational lensing.
Peace out brother no danger... yet

Posted by Sandeep Kumar S on Thursday, 10.1.15 @ 01:14am

This is extremely extraordinary. Is this activity normal to the black hole in the center of the galaxy?

Posted by Angeles cole on Tuesday, 09.29.15 @ 14:29pm

Great photos. Thanks.

Posted by paulskillman on Saturday, 09.26.15 @ 11:38am

So do we have to worry about objects hitting our Sun and like the black hole our Sun produce a flare that can destroy Earth?

Posted by paul cafaro on Saturday, 09.26.15 @ 01:15am

Years ago, my brother Anthony, my friend Joe & I observed Sagittarius A by using a shortwave radio - a simple die pole antenna. When we set the shortwave to 20.5 mega hertz, we were able to get a loud hiss which came from the central black hole.

Posted by Michael Amato on Friday, 09.25.15 @ 22:51pm

Any Black holes near the earth, any danger effects earth in future?

Posted by KARTHICK on Thursday, 09.24.15 @ 06:24am

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