The artist's impression of the remainder of a star orbiting a black hole. Image: NASA
NASA astronomers have observed a supermassive black hole spinning at 380 million miles per hour, or half the speed of light.
To put this in perspective, this means that the black hole – 300 times the diameter of the Earth – completes one rotation about every two minutes.
As detailed in an article published on Wednesday ScienceThe team made the unprecedented measurement of black hole rotation using observations from a set of space-based X-ray observatories, including NASA's Chandra telescope.
Astronomers were able to observe more than 300,000 rotational cycles, giving the most accurate measure of a supermassive black hole ever made.
The black hole, located some 290 million light years from Earth, caught the attention of astronomers in 2014 after a strong explosion of light was detected by optical telescopes. After a more detailed investigation, astronomers discovered that light was the result of a star being torn into pieces by a supermassive black hole.
An optical and radiological image of the black hole. Image: NASA
As the rest of the star fell toward the black hole's event horizon, astronomers were able to monitor the X-ray emissions the hole produced using Chandra and two other space-based telescopes. (In addition to the event horizon, no light or other energy can escape the immense black hole gravitational force.)
Because the black holes themselves do not emit any light or other energy, the only way to measure their speed of rotation is by observing other objects orbiting around them and extrapolating these observations to determine how fast the black hole is spinning. The scientists noted that X-rays would increase every 131 seconds, which they attributed to hot gas orbiting the black hole that functioned as a sort of beacon.
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This is not the first time scientists use variations on X-ray emissions to measure the turning of a black hole. Previously, however, these types of observations were limited to black holes only a few times more massive than the Sun. Although some supermassive black holes have also been observed in this way, astronomers have only been able to record some rotational cycles, which diminishes certainty of the speeds of rotation of these black holes.
According to a statement released by NASA, the researchers involved in the project hope that this will encourage astronomers to look for similar events and better understand how stars interact with black holes.