Black Hole Spin Rate Discovery May Shed Light On Evolution Of Galaxies

[Bill USA]

http://www.huffingtonpost.com/2013/07/30/black-hole-spin-rate-discovery-evolution-galaxies_n_3675578.html

A newly discovered way to determine the spin of monster black holes could help shed light on the evolution of these bizarre objects and the galaxies they anchor.

Astronomers watched as a black hole that sits at the core of a spiral galaxy 500 million light-years from Earth gobbled up gas and dust from its surrounding accretion disk. They were able to measure the distance between the inner edge of the disk and the black hole, which, in turn, allowed them to estimate the black hole's spin.

“If a black hole is spinning, it drags space and time with it, and that drags the accretion disk, containing the black hole's food, closer towards it," study lead author Chris Done, of the University of Durham in the United Kingdom, said in a statement. "This makes the black hole spin faster — a bit like an ice skater doing a pirouette."

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It's tough to describe black-hole spin rates because they don't really translate into familiar terms, such as miles per hour. For example, the NGC 1365 team, which used observations by XMM-Newton and NASA's NuStar spacecraft, found the black hole's rotation rate to be 84 percent of the maximum allowed by Einstein's theory of general relativity.

In the new study, Done and her team estimated that the black hole found 500 million light-years away — which is powering a superluminous "active galactic nucleus" known as PG1244+026 — has a relatively low spin rate.
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NASA's NuStar helps Solve riddle of Black Holes rate of Spin