Astronomers Get New Spin on Black Holes

By Cowen, Ron | Science News, June 28, 1997 | Go to article overview

Astronomers Get New Spin on Black Holes


Cowen, Ron, Science News


They swallow everything in sight, warp space and time into an unfamiliar tangle, and trap even light in their clutches. Yet for something so complex, black holes are defined by just three properties: mass, charge, and spin.

By studying how ordinary stars are whipped around by their black hole companions, astronomers have measured the mass of many of these dense, invisible objects. Although they have not yet figured out a way to detect charge, scientists now report that they have indirectly determined the spin of several small black holes--those comparable in mass to stars--in the Milky Way.

"Now that we've learned how to measure a second property, spin rate, one might say that we are two-thirds of the way to understanding black holes," says study coauthor Shuang N. Zhang of the Universities Space Research Association at NASA's Marshall Space Flight Center in Huntsville, Ala.

The measurements reveal a specific relationship between the spin of a black hole and the energy it emits as gas is pulled from an orbiting companion onto a disk of material that surrounds and feeds the hole. Some black holes expel jets of material. Black holes with highly energetic jets--those that travel at nearly the speed of light--spin the fastest and in the same direction as the disk, Zhang and his collaborators report in the June 20 Astrophysical Journal Letters

The team, which includes Wei Cui of the Massachusetts Institute of Technology and Wan Chen of NASA's Goddard Space Flight Center in Greenbelt, Md., and the University of Maryland at College Park, identified two other indicators of spin. …

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