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In the words of Frida Kahlo, everything changes, everything moves, everything revolves. This applies to many aspects of the universe, from fundamental particles to supermassive black holes. But measuring the motion of the biggest black holes is not easy. Now, using cosmic alignments across billions of years and X-ray data from NASA's Chandra Observatory, astronomers have measured how fast five supermassive black holes rotate on their axes.
The five objects observed are quasars, galaxies with a supermassive black hole so active it outshines all the stars around it. The light doesn’t come from the black hole itself (nothing escapes a black hole, not even light), but from the disk of material that surrounds it. This disk is under incredible force, gets heated up to scorching temperatures, and is spun around at phenomenal speed.
As reported in The Astrophysical Journal, in one of the quasars the material in the disk is being thrown about at 70 percent of the speed of light. This implies that the black hole’s event horizon, the surface beyond which nothing can escape, must be moving at almost the speed of light. The other four quasars are spinning at about half this maximum rate.
The five black holes have masses between 160 and 500 million times that of our Sun. Their host galaxies are located at distances ranging from 9.8 billion to 10.9 billion light-years from us. Measuring the disks around the black holes was not an easy task. The astronomers were helped by the serendipitous positions of certain foreground galaxies.
Any object with mass warps space-time, but large and/or denser bodies can bend the continuum so much that they act as lenses, magnifying the light of things in the background. These quasars are all gravitationally lensed by galaxies much closer to us. This is called strong lensing and it often produces multiple images of the same object, the so-called Einstein Cross.
On top of that already pretty handy magnification, researchers used the phenomenon of microlensing, where stars produce a magnification. Using the stars in the gravitationally lensing galaxies, the team was able to see even more details of these disks of material and produce a better estimate of the spinning rate of these incredible black holes.
