For the first time, astronomers have managed to measure the rate of spin of a supermassive black hole—and it's been clocked at 84 percent of the speed of light, or the maximum allowed by the law of physics.
"The most exciting part of this finding is the ability to test the theory of general relativity in such an extreme regime, where the gravitational field is huge, and the properties of space-time around it are completely different from the standard Newtonian case," said lead author Guido Risaliti, of the Harvard-Smithsonian Center for Astrophysics (CfA) and INAF-Arcetri Observatory in Italy. (Related: "Speedy Star Found Near Black Hole May Test Einstein Theory.")
They can pack the gravitational punch of many million or even billions of suns—distorting space-time in the region around them, not even letting light escape their clutches.
The predatory monster that lurks at the core of the relatively nearby spiral galaxy NGC 1365 is estimated to weigh in at about two million times the mass of the sun, and stretches some 2 million miles (3.2 million kilometers) across—more than eight times the distance between Earth and the moon, Risaliti said. (Also see "Black Hole Blast Biggest Ever Recorded.")
Risaliti and colleagues' unprecedented discovery was made possible thanks to the combined observations from NASA's high-energy x-ray detectors on its Nuclear Spectroscopic Telescope Array (NuSTAR) probe and the European Space Agency's low-energy, x-ray-detecting XMM-Newton space observatory.
Astronomers detected x-ray particle remnants of stars circling in a pancake-shaped accretion disk surrounding the black hole, and used this data to help determine its rate of spin.
By getting a fix on this spin speed, astronomers now hope to better understand what happens inside giant black holes as they gravitationally warp space-time around themselves.
Even more intriguing to the research team is that this discovery will shed clues to black hole's past, and the evolution of its surrounding galaxy.
Tracking the Universe's Evolution
Supermassive black holes have a large impact in the evolution of their host galaxy, where a self-regulating process occurs between the two structures.
"When more stars are formed, they throw gas into the black hole, increasing its mass, but the radiation produced by this accretion warms up the gas in the galaxy, preventing more star formation," said Risaliti.
"So the two events—black hole accretion and formation of new stars—interact with each other."
Knowing how fast black holes spin may also help shed light how the entire universe evolved. (Learn more about the origin of the universe.)
"With a knowledge of the average spin of galaxies at different ages of the universe," Risaliti said, "we could track their evolution much more precisely than we can do today."