Science
Chandra observatory to help 'weigh' giant black holes
Washington | July 17, 2008 1:05:06 PM IST
A new technique relying on data from NASA's Chandra X-ray Observatory could help weigh something as unimaginably heavy as the biggest black holes in the universe. Black holes are such dense masses that they would compress a 90,000-tonne cruise ship into the size of a teaspoon, but with the same weight. By measuring a peak in the temperature of hot gas at the centre of the giant elliptical galaxy NGC 4649, scientists determined the mass of the galaxy's super massive black hole. The method, applied for the first time, gives results consistent with traditional techniques. Astronomers have been seeking different, independent ways of precisely weighing the largest super massive black holes, billions of times more massive than the sun. Until now, methods based on observing the motions of stars or of gas in a disc near such large black holes had been used. This is tremendously important work since black holes can be elusive, and there are only a couple of ways to weigh them accurately, said Philip Humphrey, leader of the study and a scientist at the University of California at Irvine. It is reassuring that two very different ways to measure the mass of a big black hole give such similar answers, Humphrey said. NGC 4649 is now one of only a handful of galaxies for which the mass of a super massive black hole has been measured with two different methods. This new x-ray technique confirms that the NGC 4649 black hole is one of the largest, having a mass about 3.4 billion times that of the sun, about 1,000 times bigger than the black hole at the centre of our galaxy. The new technique takes advantage of the gravitational influence the black hole has on the hot gas near the centre of the galaxy. As gas slowly settles towards the black hole, it gets compressed and heated. This causes a peak in the temperature of the gas very near the centre of the galaxy. The more massive the black hole, the bigger the temperature peak detected by Chandra. These findings are scheduled to appear in the forthcoming edition of The Astrophysical Journal. St/jg (399 Words)17071224NNNN (IANS)
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