Huge black hole has supersize appetite

THE BALTIMORE SUN

Scientists have found the largest explosion to be detected so far since the big bang created the universe 13.7 billion years ago.

It's coming from a black hole the size of our solar system and, thankfully, pretty far away - about 2.6 billion light years. (A light year is 5.9 trillion miles, or about 63,000 times the distance between the Earth and the sun.)

Even so, the black hole's size and power were a shock to the astronomer who discovered it.

"When I saw it, I almost fell off my chair, I was so startled by it," said Brian McNamara, a research professor at Ohio University.

A report this month in the journal Nature says that the black hole is siphoning up matter and spraying energy across an area about 600 times the size of our Milky Way galaxy. The findings are based on observations from NASA's Chandra X-Ray Observatory.

McNamara and a team of researchers found that the black hole has created two enormous cavities as it feeds itself and sucks up the matter around it. The cavities - which show up as voids in Chandra's X-ray emissions - may be preventing stars and galaxies from forming, he said.

Based on the size of the cavities, researchers say the black hole has been erupting for 100 million years and has so far swallowed the equivalent of 300 million stars the size of our sun.

"The sheer size of it is astounding," McNamara said. "It really is hard to get your mind around."

Astronomers may one day find bigger black holes, experts say. But the study is the first to show the nature of the forces generated by the type of black holes that exist inside massive galaxy clusters.

"It shows a whole new picture of what's going on in the center of these galaxies and clusters," said Lynn Cominsky, chairwoman of the physics and astronomy department at Sonoma State University.

Black holes are mysterious masses of energy believed to be formed by the collision or collapse of massive stars. They can't be seen directly because they don't emit light - their gravitational force is so strong that light can't get out. But their existence has been confirmed by the Hubble Space Telescope and other instruments.

"We know just about every galaxy has black holes," said Joel Bregman, a University of Michigan astronomer.

Astronomers believe there are two types of black holes, Bregman said. One type is formed when massive stars die. But the other type, like the one in the Nature report, are super massive black holes found at the centers of galaxy clusters that are believed to play a role in star formation.

Most galaxy clusters share space with hot gases. Through time, the gases lose energy and cool through X-ray emissions. As they do, they form new stars and galaxies, experts say.

But over the years, astronomers peering across parts of the universe have been puzzled by the absence of cooling gases and star formation.

McNamara, intrigued by the problem, decided in the late 1990s to focus on a galaxy cluster - prosaically identified as MS 0735.6+7421 - because of a phenomenon he observed in that part of the universe using an optical telescope at Kitt Peak National Observatory in Arizona.

Astronomers had suspected that the cluster included a supermassive black hole because of its size and brightness. But in his observations at Kitt Peak, McNamara found there wasn't as much star formation as there should be.

To really understand what was happening, he needed the Chandra, which measures X-ray radiation given off by superhot gases that can't be detected by optical telescopes.

In images beamed back from Chandra in 2003, McNamara found the cavities that he thinks are preventing hot gases from cooling off and forming stars and galaxies.

Researchers from the University of Virginia, Boston University, the National Radio Astronomy Observatory and the Massachusetts Institute of Technology collaborated on the paper, published Jan. 6.

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