Super Massive Black Holes Spin Really Fast!

The terrible tidal forces near a supermassive black hole at the center of another galaxy was recently observed to have ripped apart a nearby star that fell in too close... Astronomers noted that the remnants of the torn-apart star were emitting bright X-rays, and...  

"Now researchers at MIT and elsewhere have pored through data from multiple telescopes' observations of the event, and discovered a curiously intense, stable, and periodic pulse, or signal, of X-rays, across all datasets. The signal appears to emanate from an area very close to the black hole's event horizon...The signal appears to periodically brighten and fade every 131 seconds...The researchers believe that whatever is emitting the periodic signal must be orbiting the black hole, just outside the event horizon...Given the signal's stable proximity to the black hole and the black hole's mass, which researchers previously estimated to be about 1 million times that of the sun, the team has calculated that the black hole is spinning at about 50 percent the speed of light."

(Fast enough to make you dizzy...)

It's kind of amazing.

Apparently supermassive black holes are usually rather passive and quiet as far as X-ray emissions go. But they perk up temporarily when they eat stars. The partially chewed star remnants get very bright for a while as they whirl around the black hole in its accretion disk. Now it's been shown that data on the black hole's rate of spin can be extracted from the periodicity of the emissions and the black hole's mass. (The mass determines the size of the event horizon, hence the minimum size of the orbit.) Spin data is of major interest to astrophysicists and has been something that's been very hard to determine up to now. And the really fast relativistic spin speeds makes it even more interesting...
(Jan 11, 2019 06:08 AM)Yazata Wrote: the team has calculated that the black hole is spinning at about 50 percent the speed of light.

(Fast enough to make you dizzy...)

Enough to make anything in the vicinity dizzy... it should have some interesting relativistic effects due to Frame Dragging. If a massive object is rotating, it will tend to twist space-time around itself. (This is unlike Newtonian physics, where gravity is only a function of a body's mass and not its rotation.) While frame-dragging is very small and difficult to detect around earth-sized bodies, it's important around rotating black holes. Especially supermassive black holes. And Especially supermassive black holes rotating at some significant fraction of the speed of light. This is more pronounced the closer one gets to the event horizon. There may be some very interesting and very peculiar physics near the rotating supermassive black holes lurking in the hearts of galaxies.

Something more speculative...

And something much more speculative...
Neighboring civilizations glad that it's confined to rotation, rather than a black hole traveling across space at half-light speed in their direction. (As if any complex life -- much less development of intelligence -- has a chance in the crowded and turbulent interior of a galaxy. Gamma-ray bursts, supernovas, frequent gravitational perturbations of comet clouds and asteroid belts, etc. "Hillbilly heaven: Sapience loves the rural outskirts.")

How fast can black holes spin?: "One black hole, at the heart of galaxy NGC 1365 is turning at 84% the speed of light. It has reached the cosmic speed limit, and can't spin any faster without revealing its singularity."


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