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Black Hole Spin Rate Deduced For First Time

The spin rate of a supermassive black hole has been deduced for the first time by researchers working at NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) and the European Space Agency’s XMM-Newton X-Ray telescopes.

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The black hole in question has a mass over 2 million times larger than that of the Sun. And exists at the center of a galaxy referred to by researchers as NGC 1365. The black hole is spinning at nearly the max speed as Einstein’s theory of gravity predicts is possible.

The discovery should help to resolve the ongoing debate that there has been about similar measurements taken of other black holes potentially increasing the scientific understanding of black hole and galaxy formation.


“This is hugely important to the field of black hole science,” stated Lou Kaluzienski, a researcher working at the NuSTAR program at NASA’s Headquarters in Washington.

The direct observations of the black hole’s spin rate also allow thorough testing of Einstein’s theory of general relativity to be done. According to the theory, gravity is able to warp space-time, which is the ‘fabric’ that the universe is made out of, and also the energy that travels through it, such as light.

“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 co-author of the 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.”

“NuSTAR, an Explorer-class mission launched in June 2012, is designed to detect the highest-energy X-ray light in great detail. It complements telescopes that observe lower-energy X-ray light, such as XMM-Newton and NASA’s Chandra X-ray Observatory. Scientists use these and other telescopes to estimate the rates at which black holes spin.”

Previously, there was some uncertainty about these measurements because “clouds of gas could have been obscuring the black holes and confusing the results. With help from XMM-Newton, NuSTAR was able to see a broader range of X-ray energies and penetrate deeper into the region around the black hole. 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.”

“If I could have added one instrument to XMM-Newton, it would have been a telescope like NuSTAR,” said Norbert Schartel, XMM-Newton Project Scientist at the European Space Astronomy Center in Madrid. “The high-energy X-rays provided an essential missing puzzle piece for solving this problem.”

Being able to determine the exact spin of supermassive black holes is extremely important in the field, as it allows fundamentals about the history of the universe to be clarified.

“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,” according to the study’s lead author, Guido Risaliti of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and the Italian National Institute for Astrophysics.

“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.”

“Astronomers look for these warping effects by analyzing X-ray light emitted by iron circulating in the accretion disk. In the new study, they used both XMM-Newton and NuSTAR to simultaneously observe the black hole in NGC 1365. While XMM-Newton revealed that light from the iron was being warped, 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.”

The research was just published in the journal Nature.

Source: NASA/Jet Propulsion Laboratory

Image Credits: NASA/JPL-Caltech




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