Astrophysicists had been struggling for long to figure out how black holes work, as well as to understand their mind-boggling characteristics. For a long time, nobody could come with compelling explanations for how these cosmic monsters can have infinite gravity, can literally stop time, and more. And these things will probably still remain a mystery for decades from now on.
Pretty much everything spins in the Universe: from galaxies, stars, planets, and so on. It’s also the case for black holes, but astronomers had trouble finding out the speed of their spin. Now, they have the correct answer.
Target: the 4U1543-4 black hole
This black hole exists in our own galaxy, as it’s located 24,700 light-years away from Earth. While it’s difficult to determine the speed of the spin for a black hole by usual methods, scientists didn’t run out of ideas. They had been relying on the whirling clouds of matter outside the black hole’s event horizon, and their movement is driven by the spin of the singularity. By determining how fast that matter is moving, they can estimate the spin of the singularity itself.
The key is measuring the glow of X-rays produced near the event horizon as its surrounding swirl of dust and gas accelerates to extreme speeds. The glow reveals how fast the dust and gas are moving, and that, in turn, offers information about the singularity itself.
The rate of spin for 4U1543-4
This black hole, according to the scientists involved, has a spin of 0.67. The rate of spin is “moderate” for a black hole of this mass. Astronomers generally describe a black hole’s rate of spin by numbers from -1 to 1. However, scientists admit that in the case of the 4U1543-4 black hole, there is room for some error bars around the estimate.
The study paper was published in the journal Monthly Notices of the Royal Astronomical Society, and it became available on arXiv.