Magazine article Science News

Energy-Saving Space Engines: Black Holes Can Be Green

Magazine article Science News

Energy-Saving Space Engines: Black Holes Can Be Green

Article excerpt

Some seemingly quiet black holes are actually efficient engines that emit jets of high-energy particles. This finding, from the first study to directly measure the efficiency of black holes, offers a hint as to why the universe isn't more crowded with stars.

All black holes swallow matter and spit out energy. Their gravitational pull traps clouds of hot, X-ray-emitting gas, and the black holes spew radiation or jets of high-energy particles.

The energy that black holes send out affects their environments. Scientists had presumed that young black holes producing quasars, which are beacons of light, are highly efficient. However, that efficiency hasn't been directly measured because the quasars are too bright.

Instead of focusing on quasars, a team of scientists led by astrophysicist Steven W. Allen of Stanford University used NASA's Chandra X-Ray Observatory to look at nine supermassive black holes, which are older than quasars and lie at the centers of nearby giant elliptical galaxies. "These are the boring old black holes that we thought had stopped doing anything interesting a long time ago," says team member astrophysicist Christopher S. Reynolds of the University of Maryland at College Park. The team's findings, announced this week, will be published in an upcoming Monthly Notices of the Royal Astronomical Society.

Though these black holes produce relatively little radiation, previous Chandra observations had noted the formation of large cavities in the surrounding gas clouds, as if the black holes were blowing bubbles tens of thousands of light-years across. …

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