Spinning Black Hole

Everything Spins

Spin is a characteristic of nearly every piece of matter, from the smallest sub-atomic particle to the largest galaxy. Spin (or more properly, angular momentum) is conserved, so that as the size of a rotating object decreases, its spin rate increases. The formation of a black hole represents the ultimate shrinking of matter, in which matter collapses to occupy no space. Conservation of angular momemtum suggests that black holes should spin, but what this "spin" would represent is hard to understand, since it's impossible to see inside the black hole's "event horizon". So how can the spin of a black hole be measured? A team of astronomers at the NASA/Goddard Space Flight Center think they've found one way to measure the spin of a black hole, by measuring the effect of the black hole's spin on the surrounding space. According to Einstein's theory of general relativity, a spinning black hole should drag spacetime around (so that should an astronaut come near a spinning black hole, she'd start spinning too!). The image above represents the space-time around a non-spinning black hole (left) and spinning black hole (right). Using the Rossi X-ray Timing Explorer (RXTE), these astronomers believe they've detected a signal from matter rotating with the black hole in the star system known as GRO J1655-40. "A spinning black hole modifies the fabric of spacetime near it," said Dr. Tod Strohmayer of GSFC, who lead the team which analyzed the RXTE data. "The spinning allows matter to orbit at a closer distance than if it were not spinning, and the closer matter can get the faster it can orbit." Strohmayer and his colleagues detected a signal from this innermost, fastest-moving material orbiting with the spinning black hole.

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Page Author: Dr. Michael F. Corcoran
Last modified May 14, 2001