Black Holes Are "Green," X-Ray Study Says

April 24, 2006

Supermassive black holes are actually "green," scientists announced today as they described a new study on the energy efficiency of black holes.

If cars were as fuel efficient as these black holes, researchers say, the vehicles could theoretically travel over a billion miles (1.6 billion kilometers) on a gallon of gasoline.

"In anyone's book, that would be pretty green," Steve Allen, an astrophysicist with Stanford University in Palo Alto, California, and lead author of the study, said during a telephone briefing with reporters.

Using NASA's Chandra X-ray Observatory (related images from Chandra), scientists hope to provide insight into how older, supermassive black holes at the centers of elliptical galaxies generate energy and affect their environment.

According to the study, most of the energy released by matter falling toward these supermassive black holes is in the form of high-energy jets traveling near the speed of light away from the black hole.

These jets create bubbles thousands of light-years across in the hot gas in galaxies. The energy supplied to these bubbles keeps the hot gas from cooling, thereby preventing billions of new stars from forming.

This should place limits on the growth of the largest galaxies, scientists said.

"In an environmental sense, the black holes are actually preventing galactic sprawl from taking over the neighborhood," Kimberly Weaver, an astrophysicist with the NASA Goddard Space Flight Center in Greenbelt, Maryland, said at the briefing.

Weaver, who was not part of the study team, added, "This is another way that these black holes could be considered green."

Not So Boring

Black holes are places in space where the force of gravity is so strong that nothing, not even light, can escape. Supermassive black holes are found at the center of every galaxy in the universe.

Allen and his colleagues studied nine older supermassive black holes in nearby galaxies that have received less scientific attention than quasars, a younger type of supermassive black hole.

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