Magazine article Science News

Astronomers Get the Spin on Black Holes

Magazine article Science News

Astronomers Get the Spin on Black Holes

Article excerpt

For all their mind-boggling effects on geometry, warping the very fabric of space and time, black holes are governed by two just properties--mass and spin.

Although these superdense objects don't emit light, their mass can be measured with relative ease if they are partnered with a visible star. Astronomers simply record how much of a tug a black hole exerts on its companion. Determining whether a black hole rotates has proven much more of a challenge. Astronomers reported last week strong evidence that black holes spin like whirling dervishes, dragging space-time along with them.

With the Rossi X-ray Timing Explorer satellite, Tod E. Strohmayer of NASA's Goddard Space Flight Center in Greenbelt, Md., and his colleagues examined the X-ray flashes emitted by stellar matter plunging into a nearby black hole. Known as GRO J1655-40, this system lies 10,000 light-years from Earth and consists of an ordinary star orbiting a black hole about 6.3 times as massive as the sun.

A blob of gas circling a stationary black hole this massive can't maintain itself in an orbit with a radius smaller than 64 kilometers. If the orbiting material ventures any nearer, it's doomed to fall into the black hole, never to be seen again.

From the region around GRO J1655-40, the satellite detected X rays that flicker 300 times per second. The observed rapidity is just what astronomers would expect from a blob of hot gas orbiting 64 km from the black hole. The satellite, however, also recorded an even faster flickering--an X-ray signal winking on and off 450 times per second. …

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