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NASA's Chandra Finds Milky Way's Black Hole Grazing on Asteroids

For Release: February 8, 2012


Sagittarius A*
Credit: X-ray: NASA/CXC/MIT/F. Baganoff et al.; Illustrations: NASA/CXC/M.Weiss
Press Image and Caption

WASHINGTON -- The giant black hole at the center of the Milky Way may be vaporizing and devouring asteroids, which could explain the frequent flares observed, according to astronomers using data from NASA's Chandra X-ray Observatory.

For several years Chandra has detected X-ray flares about once a day from the supermassive black hole known as Sagittarius A*, or "Sgr A*" for short. The flares last a few hours with brightness ranging from a few times to nearly one hundred times that of the black hole's regular output. The flares also have been seen in infrared data from ESO's Very Large Telescope in Chile.

"People have had doubts about whether asteroids could form at all in the harsh environment near a supermassive black hole," said Kastytis Zubovas of the University of Leicester in the United Kingdom, and lead author of the report appearing in the Monthly Notices of the Royal Astronomical Society. "It's exciting because our study suggests that a huge number of them are needed to produce these flares."

Zubovas and his colleagues suggest there is a cloud around Sgr A* containing hundreds of trillions of asteroids and comets, stripped from their parent stars. Asteroids passing within about 100 million miles of the black hole, roughly the distance between the Earth and the sun, would be torn into pieces by the tidal forces from the black hole.

These fragments then would be vaporized by friction as they pass through the hot, thin gas flowing onto Sgr A*, similar to a meteor heating up and glowing as it falls through Earth's atmosphere. A flare is produced and the remains of the asteroid are swallowed eventually by the black hole.

"An asteroid's orbit can change if it ventures too close to a star or planet near Sgr A*," said co-author Sergei Nayakshin, also of the University of Leicester. "If it's thrown toward the black hole, it's doomed."

The authors estimate that it would take asteroids larger than about six miles in radius to generate the flares observed by Chandra. Meanwhile, Sgr A* also may be consuming smaller asteroids, but these would be difficult to spot because the flares they generate would be fainter.

These results reasonably agree with models estimating of how many asteroids are likely to be in this region, assuming that the number around stars near Earth is similar to the number surrounding stars near the center of the Milky Way.

"As a reality check, we worked out that a few trillion asteroids should have been removed by the black hole over the 10-billion-year lifetime of the galaxy," said co-author Sera Markoff of the University of Amsterdam in the Netherlands. "Only a small fraction of the total would have been consumed, so the supply of asteroids would hardly be depleted."

Planets thrown into orbits too close to Sgr A* also should be disrupted by tidal forces, although this would happen much less frequently than the disruption of asteroids, because planets are not as common. Such a scenario may have been responsible for a previous X-ray brightening of Sgr A* by about a factor of a million about a century ago. While this event happened many decades before X-ray telescopes existed, Chandra and other X-ray missions have seen evidence of an X-ray "light echo" reflecting off nearby clouds, providing a measure of the brightness and timing of the flare.

"This would be a sudden end to the planet's life, a much more dramatic fate than the planets in our solar system ever will experience," Zubovas said.

Very long observations of Sgr A* will be made with Chandra later in 2012 that will give valuable new information about the frequency and brightness of flares and should help to test the model proposed here to explain them. This work could improve understanding about the formation of asteroids and planets in the harsh environment of Sgr A*.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

For Chandra images, multimedia and related materials, visit:

For an additional interactive image, podcast, and video on the finding, visit:

Media contacts:
Trent J. Perrotto
Headquarters, Washington

Megan Watzke
Chandra X-ray Center, Cambridge, Mass.

Visitor Comments (12)

(part 2) My impression: The region around Sagittarius A (further refered as "SA" is milky way`s central black hole) flashing up again and again (by matter falling into it). Other- obviously large- stars AROUND have strong activity fluctuations under its influence. Esp. the star right above SA is already loosing much of izs mass,and a long tail of gases leads towards SA In one moment this star seems even split into two/ into half and reunites again after. . At the end of the clip just another star suddenly appears resp shines up right in the image...

Posted by helmut on Thursday, 10.11.12 @ 16:45pm

I just discovered this side. Great work!! Especially that video here made by Chandra form the galactic center ( Sagit. A). What it shows says much. But- it would be kind, if any of you NASA expert would make a comment on it what he/she believes this video actually shows.! read ff2

Posted by helmut on Thursday, 10.11.12 @ 16:44pm

Dear Massimo Calvani,
Thanks very much for your comment. I am aware that the work of Kostic et al. is referenced by Zubovas et al. I will email you with some suggestions for further recognition of the work by Kostic et al.
-P.Edmonds, CXC

Posted by P. Edmonds on Tuesday, 02.14.12 @ 10:11am

Dear kiyohisa,
There will be material - mainly hot gas - around the outside of the event horizon. This will eventually pass over the event horizon, never to be seen again, unless some process like a wind or a jet ejects it. I do not believe that secret passages (like wormholes) are generally being invoked by researchers to understand material falling onto black holes.
-P.Edmonds, CXC

Posted by P. Edmonds on Tuesday, 02.14.12 @ 10:07am

Dear Mike Delaney,
Thankfully, the Earth is not being drawn towards Sgr A*. There are *much* stronger sources of gravity, such as the Sun and the Moon.
-P.Edmonds, CXC

Posted by P. Edmonds on Tuesday, 02.14.12 @ 10:05am

Dear Mike Delaney,
It's believed that black holes can radiate in a process called Hawking radiation, although this is believed to take an extremely long time for astrophysical black holes.
-P.Edmonds, CXC

Posted by P. Edmonds on Tuesday, 02.14.12 @ 10:02am

Dear Wilhelm Koen,
Good comment - the authors estimate that about 10% of the rest mass of the asteroid will be converted into energy, although all of this might not go into X-rays.
-P.Edmonds, CXC

Posted by P. Edmonds on Tuesday, 02.14.12 @ 09:57am


Is this E(X-Ray)=m(Asteroid)xc²?

Posted by Wilhelm Koen on Saturday, 02.11.12 @ 23:32pm

All is not lost. Even if we have not observed any, Black holes can dissipate on their own.
Some tornadoes don't reach ground, they just disappear on their own into the atmosphere.

Posted by Mike Delaney on Friday, 02.10.12 @ 21:59pm

How quickly are we (earth) being drawn toward sag A? Can we estimate how long it will take us to be drawn into it?

Posted by Mike Delaney on Friday, 02.10.12 @ 19:17pm

Will the circumference of the black hole have "the dust which is not absorbed in the center" around?
Or is there "a secret passage" in a law of the physics?
Still mystery many "black holes"
NASA expects discovery to surprise people of the world from now on.

Posted by kiyohisa tanada on Friday, 02.10.12 @ 06:45am

This scenario was discussed already by Dr. Uros Kostic (Faculty of Mathematics and Physics, University of Ljubljana,)in his PhD Thesis, and published in A&A in 2008-2009.
As far as I know, this is the FIRST suggestion that SgrA* flares might be due to accretion and tidal disruption of asteroids and comets.

Posted by Massimo Calvani on Friday, 02.10.12 @ 05:36am