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Science : Images from the edge of darkness

作者:俞埔莲    发布时间:2019-02-27 04:11:04    

By Jeff Kanipe Toronto, Canada NO ONE will ever see a black hole, because light cannot escape from them. But American researchers say they have found the most direct evidence yet of the “event horizons”—the boundary beyond which matter and energy cannot return —of four black holes. Ramesh Narayan, Jeffrey McClintock and Michael Garcia from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, examined satellite images of nine X-ray novae, in which stars orbit compact invisible sources such as black holes or neutron stars. Gas from the orbiting star flows steadily towards the more compact object in a process called “accretion”, in which the gas is drawn into a disc around the central object. Friction within the rapidly rotating accretion disc heats the gas up to extraordinarily high temperatures, often up to a million million degrees, which is why it radiates X-rays. The researchers found that although all nine systems are accreting gas, four of them are dimmer than the others. They claim that the dimmer novae have a black hole at their centre, and that nearly all of their thermal energy is vanishing across the black hole’s event horizon, rather than being radiated out into space. In the brighter novae, they say, the thermal energy is being reradiated from the surface of a neutron star. When the superheated gas reaches the event horizon it disappears “down the drain” into the black hole, taking its enormous thermal energy with it. “This is the most direct evidence scientists have had that black holes are real,” claims Narayan. And, he adds,

 

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