We picture black holes as giant, unmoving nothings in space, their gravitational force so crushing that everything nearby is sucked in. It's true that black holes absorb all sorts of matter, but it's not true that they do it as totally motionless voids. In fact, a recent study from NASA and the European Space Agency found that a black hole at the center of a nearby galaxy rotates as it sucks in everything around it. And it rotates at an estimated 670 million miles per hour.
That's nearly the speed of light--light travels at the speed of 671 million miles per hour, and scientists believe nothing can go faster. But black holes, apparently, can get close. NASA's NuSTAR telescope, launched in 2012, and the ESA's XMM-Newton were used together to study the black hole 60 million light years away in galaxy NGC 1365.
A NASA press release from Wednesday explains how the telescopes were able to determine that the black hole was rotating:
" '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 and 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.' "
Both telescopes were crucial in the study. XMMM-Newton was designed to detect low-energy x-rays, while the NuSTAR was designed to detect high-energy x-rays. Using only one telescope, scientists weren't sure that they could get accurate readings through clouds of dust obscuring the black hole. But with two, they could detect more x-rays and determine that the black hole was warping them with its gravitational force.
Once they could detect that warping and discount cloud interference, they could measure it:
"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....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."
NASA says that knowing the spin rate of a galaxy can help us understand its history and that of the galaxy that contains it--perhaps how old the galaxy is, how much mass the black hole has absorbed, or even if the galactic core is comprised of several black holes that merged with other black holes when galaxies collided.