February 28, 2013 – NASA’s NuSTAR Helps Solve Riddle of Black Hole Spin: Two X-ray space observatories have teamed up to measure definitively, for the first time, the spin rate of a black hole with a mass 2 million times that of our sun.
The supermassive black hole lies at the dust- and gas-filled heart of a galaxy called NGC 1365, and it is spinning almost as fast as Einstein’s theory of gravity will allow. The findings resolve a long-standing debate about similar measurements in other black holes and will lead to a better understanding of how black holes and galaxies evolve.
The observations also are a powerful test of Einstein’s theory of general relativity, which says gravity can bend space-time, the fabric that shapes our universe, and the light that travels through it.
“We can trace matter as it swirls into a black hole using X-rays emitted from regions very close to the black hole,” said the coauthor of a new study, NuSTAR principal investigator Fiona Harrison of the California Institute of Technology in Pasadena. “The radiation we see is warped and distorted by the motions of particles and the black hole’s incredibly strong gravity.”
The new data demonstrate that X-rays are not being warped by the clouds, but by the tremendous gravity of the black hole. This proves that spin rates of supermassive black holes can be determined conclusively.
Measuring the spin of a supermassive black hole is fundamental to understanding its past history and that of its host galaxy.
These monsters, with masses from millions to billions of times that of the sun, are formed as small seeds in the early universe and grow by swallowing stars and gas in their host galaxies, merging with other giant black holes when galaxies collide, or both.
Supermassive black holes are surrounded by pancake-like accretion disks, formed as their gravity pulls matter inward. Einstein’s theory predicts the faster a black hole spins, the closer the accretion disk lies to the black hole. The closer the accretion disk is, the more gravity from the black hole will warp X-ray light streaming off the disk.
NuSTAR proved that this distortion was coming from the gravity of the black hole and not gas clouds in the vicinity. NuSTAR’s higher-energy X-ray data showed that the iron was so close to the black hole that its gravity must be causing the warping effects.
With the possibility of obscuring clouds ruled out, scientists can now use the distortions in the iron signature to measure the black hole’s spin rate. The findings apply to several other black holes as well, removing the uncertainty in the previously measured spin rates.
For more information on NASA’s NuSTAR mission, visit: http://www.nasa.gov/nustar .
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