Washington, Dec 21 : Scientists have been able to determine how often the biggest black holes have been active over the last few billion years, thanks to a new study from NASA''s Chandra X-ray Observatory.
The breakthrough could help them understand better how massive stars explode, which ones leave behind black holes or neutron stars, and how many black holes are in our galaxy and others.
"We''ve found that only about one percent of galaxies with masses similar to the Milky Way contain supermassive black holes in their most active phase," said Daryl Haggard of the University of Washington in Seattle, WA, and Northwestern University in Evanston, IL.
"Trying to figure out how many of these black holes are active at any time is important for understanding how black holes grow within galaxies and how this growth is affected by their environment,” he added.
The team used a survey called the Chandra Multiwavelength Project, which covers 30 square degrees on the sky. Combining Chandra''s X-ray images with optical images from the Sloan Digital Sky Survey, about
100,000 galaxies were analyzed. Out of those, about 1,600 were X-ray bright, signaling possible AGN activity.
"This is the first direct determination of the fraction of field galaxies in the local Universe that contain active supermassive black holes," said co-author Paul Green of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA.
One result is that the fraction of galaxies containing AGN depends on the mass of the galaxy. Another result is that a gradual decrease in the AGN fraction is seen with cosmic time since the Big Bang.
The study also has important implications for understanding how the neighbourhoods of galaxies affects the growth of their black holes.
"It seems that really active black holes are rare but not antisocial. This has been a surprise to some, but might provide important clues about how the environment affects black hole growth,” said Haggard.
These results were published in the November 10th issue of the Astrophysical Journal. (ANI)
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