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Sagittarius A*: Milky Way's Black Hole Shows Signs of Increased Chatter
Sagittarius A*

  • A long monitoring campaign of the Milky Way's supermassive black hole has revealed some unusual activity.

  • Typically relatively quiet, the black hole (called Sagittarius A*) had an increase in X-ray flares in mid-2014.

  • The timing of this surge coincided with the close passage of the mysterious G2 object near the black hole.

  • Astronomers will continue to observe the black hole to ascertain the true nature of the increased X-ray activity.

Three orbiting X-ray telescopes have been monitoring the supermassive black hole at the center of the Milky Way galaxy for the last decade and a half to observe its behavior, as explained in our latest press release. This long monitoring campaign has revealed some new changes in the patterns of this 4-million-solar-mass black hole known as Sagittarius A* (Sgr A*).

The bottom panel of this graphic is a view of the region around Sgr A* where red, green, and blue represent low, medium, and high-energy X-rays detected by NASA's Chandra X-ray Observatory. Sgr A* itself is not visible in this image, but is embedded in the white dot at the end of the arrow. The other two telescopes involved in the 15 years of X-ray observations were ESA's XMM-Newton and NASA's Swift Gamma Ray Burst Explorer, but their data are not included in this image.

Within the past year, the usually quiet black hole has shown an increased level of X-ray flares over its typical rate. This surge in X-ray flares coincides with the passage close to Sgr A* of a mysterious object called G2. Astronomers have been tracking G2 for years, originally thinking it 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 a gas cloud, but instead a star or pair of stars within an extended dusty cocoon.

If the G2 explanation does explain the recent rise in X-ray flares, it 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, resulting in an enhanced feeding rate and the production of X-ray flares. This scenario is depicted in the artist's illustrations found in the upper two panels of the graphic.

While the timing of G2's passage with the surge in X-rays from Sgr A* is intriguing, it is not yet an open-and-shut case. That is because astronomers see other black holes that appear to have behavior similar to the most recent increase of activity from Sgr A*. Therefore, it's possible this increased chatter from Sgr A* may be a common trait among supermassive black holes and unrelated to G2. Instead, it could represent, for example, a change in the strength of winds from nearby massive stars that are feeding the black hole.

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. The newest set of Chandra, XMM and Swift observations, obtained between August 30 and October 2014, revealed six bright flares within about three days, while an average of only 0.8 bright flares was expected.

A paper on these findings has been accepted by the Monthly Notices of the Royal Astronomical Society and a preprint is available online. The authors of this study were Gabriele Ponti (Max Planck Institute for Extraterrestrial Physics), Barbara De Marco (Max Planck), Mark Morris (University of California, Los Angeles), Andrea Merloni (Max Planck), Teo Muñoz-Darias (University of La Laguna, Spain), Maica Clavel (CEA Saclay, France), Darryl Haggard (Amherst College), Shuo Zhang (Columbia University), Kirpal Nandra (Max Planck), Stefan Gillassen (Max Planck), Kenji Mori (Columbia), Joseph Nielsen (Massachusetts Institute of Technology), Nanda Rea (University of Amsterdam), Natalie Degenaar (University of Cambridge), Regis Terrier (University of Paris), and Andrea Goldwurm (CEA Saclay).

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.

Fast Facts for Sagittarius A*:
Credit  NASA/CXC/MPE/G.Ponti et al; Illustration: NASA/CXC/M.Weiss
Release Date  September 23, 2015
Scale  Image is 5 by 5 arcmin (about 38 light years)
Category  Black Holes, Milky Way Galaxy
Coordinates (J2000)  RA 17h 45m 40s | Dec -29 00' 28.00"
Constellation  Sagittarius
Observation Date  43 pointings from September 21, 1999 to May 18, 2009
Observation Time  278 hours (11 days 14 hours).
Obs. ID  242, 1561, 2943, 2951-2954, 3392, 3393, 3549, 3663, 3665, 4683, 4684, 5360, 5950-5954, 6113, 6363, 6639, 6640-6646, 7554-7759, 9169-9174, 10556
Instrument  ACIS
Also Known As Galactic Center
References Ponti, G et al, 2015, MNRAS (accepted); arXiv:1407.2243
Color Code  Energy: Red (2-3.3 keV), Green (3.3-4.7 keV), Blue (4.7-8 keV)
Distance Estimate  About 26,000 light years
distance arrow
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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