Astronomers have measured the rate of spin of a supermassive black hole for the first time - and it is big.
Measurements undertaken with two space-based X-ray telescopes imaged the black hole at the centre of galaxy NGC 1365.
The spin measurement, published in Nature, gives precious clues as to how the black hole grew and achieved supermassive status.
That growth influences the evolution of galaxies, so this simple number stands to teach scientists a great deal.
Black holes are notoriously difficult to study, since so much in astronomy depends on the detection of light - and beyond a certain distance, even that cannot escape.
Black holes are known to draw in material - gas and even stars - and stretching the very fabric of space-time at their edges. As matter goes in and gathers into what is called an accretion disk, it heats up and emits X-rays.
Previous attempts to quantify black holes' spins have attempted to analyse these X-rays - accounting for the violent processes within that can stretch and distort the X-rays' energies.
Those studies have until now focused on a fairly low-energy X-ray range. But those lower-energy X-rays can be further distorted by layers of gas between the black hole and the Earth, and previous spin observations have been contentious.
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Very interesting.
