Magazine article Science News

X-Rays from Dim Space Hint at a Black Hole

Magazine article Science News

X-Rays from Dim Space Hint at a Black Hole

Article excerpt

Last month an object in the constellation Perseus that had been so dim no one had ever detected it began spewing out a barrage of X-rays and gamma rays. NASA's Compton Gamma Ray Observatory (GRO) found that the puzzling source had become the most powerful radiator detected at the X-ray energy of 100,000 electron-volts.

Preliminary evidence now suggests that the object belongs to a special class of binary stars likely to contain a small black hole. Variously dubbed Nova Persei 1992 or GRO jo422+32 for its location in the sky or the observatory that discovered it, the object has X-ray and ultraviolet spectra resembling those of other candidate black holes that have literally burst on the scene in the past 20 months. Researchers reported some of their findings last week at the World Space Congress in Washington, D.C.

Nova Persei 1992 appears to belong to a subtype of a general class of X-ray-emitting stars called low-mass X-ray binaries. Low-mass binaries typically feature a dwarf star closely orbiting a highly compact object, either a neutron star or a black hole. (A black hole is a collapsed star theorized to have such a strong gravitational field that not even light can escape it.) Matter from the dwarf star falls directly onto its compact partner or onto a disk of matter surrounding that partner, emitting intense radiation in the process. Many binaries emit light continuously, masking the faint glow of the dwarf star. But some binaries, perhaps including Nova Persei 1992, emit radiation in bursts that die down after a few months, allowing researchers to observe the dim dwarf star and estimate its mass and velocity, From such data, scientists can determine if the dwarf's compact partner has more than three times the mass of the sun -- the minimum value a star must have to become a black hole. …

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