[meteorite-list] NASA's Chandra Detects Record-Breaking Outburst from Milky Way's Black Hole

[Ron Baalke]

January 5, 2015
     
NASA's Chandra Detects Record-Breaking Outburst from Milky Way's Black Hole

Astronomers have observed the largest X-ray flare ever detected from the 
supermassive black hole at the center of the Milky Way galaxy. This event, 
detected by NASA's Chandra X-ray Observatory, raises questions about the 
behavior of this giant black hole and its surrounding environment.

The supermassive black hole at the center of our galaxy, called Sagittarius 
A*, or Sgr A*, is estimated to contain about 4.5 million times the mass of 
our sun.

Astronomers made the unexpected discovery while using Chandra to observe how 
Sgr A* would react to a nearby cloud of gas known as G2.

"Unfortunately, the G2 gas cloud didn't produce the fireworks we were 
hoping for when it got close to Sgr A*," said lead researcher Daryl Haggard 
of Amherst College in Massachusetts. "However, nature often surprises us 
and we saw something else that was really exciting."

On Sept. 14, 2013, Haggard and her team detected an X-ray flare from Sgr A* 
400 times brighter than its usual, quiet state. This "megaflare" was 
nearly three times brighter than the previous brightest X-ray flare from Sgr 
A* in early 2012. After Sgr A* settled down, Chandra observed another 
enormous X-ray flare 200 times brighter than usual on Oct. 20, 2014.

Astronomers estimate that G2 was closest to the black hole in the spring of 
2014, 15 billion miles away. The Chandra flare observed in September 2013 was 
about a hundred times closer to the black hole, making the event unlikely 
related to G2.

The researchers have two main theories about what caused Sgr A* to erupt in 
this extreme way. The first is that an asteroid came too close to the 
supermassive black hole and was torn apart by gravity. The debris from such a 
tidal disruption became very hot and produced X-rays before disappearing 
forever across the black hole's point of no return, or event horizon.

"If an asteroid was torn apart, it would go around the black hole for a 
couple of hours - like water circling an open drain - before falling 
in," said co-author Fred Baganoff of the Massachusetts Institute of 
Technology in Cambridge, Massachusetts. "That's just how long we saw the 
brightest X-ray flare last, so that is an intriguing clue for us to 
consider."

If this theory holds up, it means astronomers may have found evidence for the 
largest asteroid to produce an observed X-ray flare after being torn apart by 
Sgr A*.

A second theory is that the magnetic field lines within the gas flowing 
towards Sgr A* could be tightly packed and become tangled. These field lines 
may occasionally reconfigure themselves and produce a bright outburst of 
X-rays. These types of magnetic flares are seen on the sun, and the Sgr A* 
flares have similar patterns of intensity.

"The bottom line is the jury is still out on what's causing these giant 
flares from Sgr A*," said co-author Gabriele Ponti of the Max Planck 
Institute for Astrophysics in Garching, Germany. "Such rare and extreme 
events give us a unique chance to use a mere trickle of infalling matter to 
understand the physics of one of the most bizarre objects in our galaxy."

In addition to the giant flares, the G2 observing campaign with Chandra also 
collected more data on a magnetar: a neutron star with a strong magnetic 
field, located close to Sgr A*. This magnetar is undergoing a long X-ray 
outburst, and the Chandra data are allowing astronomers to better understand 
this unusual object.

These results were presented at the 225th meeting of the American 
Astronomical Society being held in Seattle. 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.

NASA is exploring our solar system and beyond to understand the universe and 
our place in it. The agency seeks to unravel the secrets of our universe, its 
origins and evolution, and search for life among the stars.

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

http://chandra.si.edu 

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

http://www.nasa.gov/chandra 

-end-

Felicia Chou
Headquarters, Washington
202-358-0257
felicia.chou at nasa.gov 

Janet Anderson
Marshall Space Flight Center, Huntsville, Ala.
256-544-6162
janet.l.anderson at nasa.gov 

Megan Watzke
Chandra X-ray Center, Cambridge, Mass.
617-496-7998
mwatzke at cfa.harvard.edu