June 15, 2011

Black Holes Were Common During Early Stages Of Universe

NASA said on Wednesday that astronomers have found the first evidence that black holes were common in the early universe.

The new discovery shows that very young black holes grew more aggressively than previously thought and in tandem with the growth of their host galaxies.  NASA's Chandra X-ray Observatory was used to help make this discovery.

NASA said by pointing Chandra to a patch of sky for more than six weeks, astronomers obtained the Chandra Deep Field South (CDFS).  When this was combined with infrared images from NASA's Hubble Space Telescope, the new Chandra data allowed astronomers to search for black holes in 200 distant galaxies, from when the universe was between about 800 million to 950 million years old.

"Until now, we had no idea what the black holes in these early galaxies were doing, or if they even existed," Ezequiel Treister of the University of Hawaii and lead author of the study said in a press release. "Now we know they are there, and they are growing like gangbusters."

The growth means that black holes in the CDFS are less extreme versions of quasars.  However, sources in the CDFS are about a hundred times fainter and the black holes are about a thousand times less massive than the ones in quasars.

NASA said observations found between 30 and 100 percent of the distant galaxies contain growing supermassive black holes.  By extending the application of these results from the small-observed field to the full sky, the team found there are at least 30 million supermassive black holes in the early universe.

"It appears we've found a whole new population of baby black holes," co-author Kevin Schawinski of Yale University said in a statement. "We think these babies will grow by a factor of about a hundred or a thousand, eventually becoming like the giant black holes we see today almost 13 billion years later."

Detailed calculations show that the number of black hole growth in the early universe observed by this team is about a hundred times higher than recent estimates.

NASA said physicists studying black holes want to know more about how the first supermassive black holes were formed and how they grow. 

"Most astronomers think in the present-day universe, black holes and galaxies are somehow symbiotic in how they grow," Priya Natarajan, a co-author from Yale University, said in a statement. "We have shown that this codependent relationship has existed from very early times."

Some theories say early black holes would play an important role in clearing away the cosmic "fog" of neutral hydrogen that pervaded the early universe when temperatures cooled down after the Big Bang.

However, NASA said this Chandra study shows that blankets of dust and gas stop ultraviolet radiation generated by the black holes from traveling outwards to perform this "reionization."  This means stars and not growing black holes are likely to have cleared this fog during the early stages of the universe.

Chandra is capable of detecting faint objects at long distances, but NASA said these black holes are so obscured that relatively few photons can escape and could not be individually detected. 

This caused the team to use a technique that relied on Chandra's ability to determine the direction the X-rays came to add up all the X-ray counts near the positions of distant galaxies and find a statistically significant signal.


Image Caption: Artist impression of a growing supermassive black hole located in the early universe. (NASA/CXC/A.Hobart) 


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