In A Spin Over Black Holes
By Hayley Birch
Just the mention of black holes and binary systems might be enough to put your head in a spin. But even astrophysicists have been left giddy by new evidence that suggests some black holes rotate at a dizzying 950 times a second – which is pretty much the predicted limit for how fast anything can rotate.
Now let’s think about this. A racing car engine rotates at roughly 15,000 rpm; that’s still only 250 times a second. A merry-go-round barely gets round every couple of seconds and that’s still probably fast enough to reduce you to a stagger. With the possible exception of Darcey Bussell, Britain’s premier ballerina, it’s pretty unlikely anyone could survive a spinning speed of 950 per second. So the moral of the story is don’t go poking about around black holes, not that you’d want to anyway.
Black holes are every bit as frightening as their name suggests. They occur when a star collapses in on itself, setting up a gravitational pull so strong that anything within a several thousand kilometre radius gets dragged in.
So imagine it’s 2025. You’re trundling along in your spaceship, minding your own business, when whoops; just like that you’re sucked into a big ol’ hole. Add to that a rotation speed of 950 times a second and you’ve got one hell of a scary way to die.
But how do scientists know that black holes rotate that fast? Well, in actual fact, the void in question is a particularly high-speed one. GRS 1915, as it is known, is a real giant, thought to have a mass 14 times greater than the sun. Its spin was measured by Jeffrey McClintock and Ramesh Narayan at Harvard University. As part of a binary system, GRS 1915 orbits around a star, gathering a visible spiral of gas as it spins and emitting x-rays. By observing the black hole through powerful x-ray telescopes, the scientists were able to figure out how hot these x-rays were. This tells them the radius – smaller holes are hotter – which is related to the speed.
Now let’s think about this. A racing car engine rotates at roughly 15,000 rpm; that’s still only 250 times a second. A merry-go-round barely gets round every couple of seconds and that’s still probably fast enough to reduce you to a stagger. With the possible exception of Darcey Bussell, Britain’s premier ballerina, it’s pretty unlikely anyone could survive a spinning speed of 950 per second. So the moral of the story is don’t go poking about around black holes, not that you’d want to anyway.
Black holes are every bit as frightening as their name suggests. They occur when a star collapses in on itself, setting up a gravitational pull so strong that anything within a several thousand kilometre radius gets dragged in.
So imagine it’s 2025. You’re trundling along in your spaceship, minding your own business, when whoops; just like that you’re sucked into a big ol’ hole. Add to that a rotation speed of 950 times a second and you’ve got one hell of a scary way to die.
But how do scientists know that black holes rotate that fast? Well, in actual fact, the void in question is a particularly high-speed one. GRS 1915, as it is known, is a real giant, thought to have a mass 14 times greater than the sun. Its spin was measured by Jeffrey McClintock and Ramesh Narayan at Harvard University. As part of a binary system, GRS 1915 orbits around a star, gathering a visible spiral of gas as it spins and emitting x-rays. By observing the black hole through powerful x-ray telescopes, the scientists were able to figure out how hot these x-rays were. This tells them the radius – smaller holes are hotter – which is related to the speed.
This illustration shows a swirling disk of gas orbiting a black hole, with the bulk of the X-rays pouring out of the inner, white-shaded region of the disk. One remarkable prediction of Einstein's relativity theory is the existence of a smallest radius for the disk, inside of which the gas suddenly plunges into the hole with no time to radiate away its energy. For the non-spinning black hole shown at left, this inner radius is large, which leaves a big dark hole cut out of the center of the hot disk of gas. For the fast-spinning black hole shown at right, the gas can orbit very near the event horizon, and thus only a small portion of the inner disk is missing. Therefore, the radius of the hole is a direct measure of the spin. Credit: NASA/NASA/CXC/M.Weiss
To find out more about Hayley or read more of her articles click here.
To find out more about Hayley or read more of her articles click here.
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