What do you get when one black hole plunges into another? A whole lot of space-shaking violence, according to the first 3-dimensional simulation of such a collision. The results will guide physicists who search for eerie distortions of space, called gravitational waves, that ripple from merging black holes and other superlative explosions.
Understanding how black holes behave requires Einstein's general theory of relativity in all its mathematical glory. The equations lead to infinite densities of matter, time that slows to a standstill, and other bizarre effects. When computer models tried to simulate these phenomena for two black holes in a death spiral, the simulations "crashed and burned," says astrophysicist Joan Centrella of NASA's Goddard Space Flight Center in Greenbelt, Maryland. As a result, physicists could not predict the patterns of gravitational disturbances that cascade into space at the speed of light from the site of a merger.
Now, Centrella and her colleagues have overcome that barrier by devising new formulations of Einstein's equations. The trick was expanding them in a way that translated exactly into computer code. The team ran its programs for several days last year on NASA's most powerful supercomputer. In the simulation, two identical, nonrotating black holes whirl around each other for several orbits and then collide. The violent interaction converts about 3% of the system's mass into a blaze of gravitational radiation, briefly emitting more energy than all stars in the universe combined. The resulting frenzy of gravitational waves is surprisingly regular, says Centrella, like sound waves that crescendo smoothly to a peak in volume and frequency and then sharply drop off. She described the work today during a NASA teleconference; the findings will be published in upcoming issues of Physical Review Letters and Physical Review D.
The simulation offers crucial new clues for physicists at the Laser Interferometer Gravitational-wave Observatory (LIGO), an experiment designed to detect the faint trembles of waves from collisions hundreds of millions of light-years away. "The calculations definitely have the ring of truth to them," says LIGO spokesperson Peter Saulson, a physicist at Syracuse University in New York. But researchers also must simulate crashes between rapidly spinning black holes of different masses, Saulson says, because that's probably how nature works. Those models--now in progress--will produce more complex patterns of gravitational waves for LIGO's physicists to try to recognize, he notes.
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