LONDON - Astronomers have weighed a supermassive black hole on the edge of the known universe and found that it is three billion times bigger than the Sun.
The black hole is 13 billion light years away on the further reaches of space, and can only be seen because it is
in a quasar, a highly energetic galaxy emitting vast amounts of light. It was examined by an Anglo-Canadian team of scientists using the United Kingdom Infrared Telescope (Ukirt) in Hawaii.
Black holes are so dense that their gravity can prevent the escape of light. A quasar is powered by the release of gravitational energy as matter is pulled toward a supermassive black hole at its centre, a process called accretion.
The extreme brightness of quasars made them visible over great distances, said Chris Willott, the team's leader from the Canadian National Research Council's Herzberg Institute of Astrophysics in Victoria, British Columbia.
The scientists used Ukirt to observe the most distant known quasar, called SDSS J1148+5251. "We're seeing this quasar as it looked when its light was emitted 13 billion years ago," Dr Willott said.
Special devices on the telescope measured the spectrum of the light from the quasar, focusing on the part made by charged magnesium particles. These magnesium ions are part of the gas circulating around the black hole at the heart of the quasar.
"We can determine the mass of the black holes in these distant quasars by looking at the [magnesium] emission line and comparing it with the same emission line in closer quasars.
"The basic idea here is that the width of the line gives an indication of the speed of the gas close to the quasar. More massive black holes will have faster moving material," Dr Willott said.
Ross McLure from the Institute for Astronomy in Edinburgh said: "This quasar ... confirms predictions that such huge black holes do exist so early in the universe, but they are rare."The research was published yesterday in the online edition of Astrophysical Journal Letters.
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