Tuesday, June 5, 2012

Black Hole Ejected from Host Galaxy


June 4, 2012

J.D. Harrington 
Headquarters, Washington 
202-358-5241 
j.d.harrington@nasa.gov 

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

RELEASE: 12-182

GIANT BLACK HOLE KICKED OUT OF HOME GALAXY

WASHINGTON -- Astronomers have found strong evidence that a massive 
black hole is being ejected from its host galaxy at a speed of 
several million miles per hour. New observations from NASA's Chandra 
X-ray Observatory suggest that the black hole collided and merged 
with another black hole and received a powerful recoil kick from 
gravitational wave radiation. 

"It's hard to believe that a supermassive black hole weighing millions 
of times the mass of the sun could be moved at all, let alone kicked 
out of a galaxy at enormous speed," said Francesca Civano of the 
Harvard-Smithsonian Center for Astrophysics (CfA), who led the new 
study. "But these new data support the idea that gravitational waves 
-- ripples in the fabric of space first predicted by Albert Einstein 
but never detected directly -- can exert an extremely powerful 
force." 

Although the ejection of a supermassive black hole from a galaxy by 
recoil because more gravitational waves are being emitted in one 
direction than another is likely to be rare, it nevertheless could 
mean that there are many giant black holes roaming undetected out in 
the vast spaces between galaxies. 

"These black holes would be invisible to us," said co-author Laura 
Blecha, also of CfA, "because they have consumed all of the gas 
surrounding them after being thrown out of their home galaxy." 

Civano and her group have been studying a system known as CID-42, 
located in the middle of a galaxy about 4 billion light years away. 
They had previously spotted two distinct, compact sources of optical 
light in CID-42, using NASA's Hubble Space Telescope. 

More optical data from the ground-based Magellan and Very Large 
Telescopes in Chile supplied a spectrum (that is, the distribution of 
optical light with energy) that suggested the two sources in CID-42 
are moving apart at a speed of at least 3 million miles per hour. 

Previous Chandra observations detected a bright X-ray source likely 
caused by super-heated material around one or more supermassive black 
holes. However, they could not distinguish whether the X-rays came 
from one or both of the optical sources because Chandra was not 
pointed directly at CID-42, giving an X-ray source that was less 
sharp than usual. 

"The previous data told us that there was something special going on, 
but we couldn't tell if there were two black holes or just one," said 
another co-author Martin Elvis, also of CfA. "We needed new X-ray 
data to separate the sources." 

When Chandra's sharp High Resolution Camera was pointed directly at 
CID-42, the resulting data showed that X-rays were coming only from 
one of the sources. The team thinks that when two galaxies collided, 
the supermassive black holes in the center of each galaxy also 
collided. The two black holes then merged to form a single black hole 
that recoiled from gravitational waves produced by the collision, 
which gave the newly merged black hole a sufficiently large kick for 
it to eventually escape from the galaxy. 

The other optical source is thought to be the bright star cluster that 
was left behind. This picture is consistent with recent computer 
simulations of merging black holes, which show that merged black 
holes can receive powerful kicks from the emission of gravitational 
waves. 

There are two other possible explanations for what is happening in 
CID-42. One would involve an encounter between three supermassive 
black holes, resulting in the lightest one being ejected. Another 
idea is that CID-42 contains two supermassive black holes spiraling 
toward one another, rather than one moving quickly away. 

Both of these alternate explanations would require at least one of the 
supermassive black holes to be very obscured, since only one bright 
X-ray source is observed. Thus the Chandra data support the idea of a 
black hole recoiling because of gravitational waves. 

These results will appear in the June 10 issue of The Astrophysical 
Journal. 

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

For Chandra images, multimedia and related materials, visit: 

http://www.nasa.gov/chandra 

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

http://chandra.si.edu 

 
-end-

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