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Astronomers Spot A Black Hole That Looks Just Like A Bullseye

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Caroline Reid

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1072 Astronomers Spot A Black Hole That Looks Just Like A Bullseye
Rings of X-ray light centered on V404 Cygni, a binary system containing an erupting black hole (dot at center). Andrew Beardmore/Univ. of Leicester, and NASA/Swift.

Far off into the night sky, a satellite saw something unexpected. A target that looks like it could be for galactic archery, complete with a black hole bullseye. The system photographed is called V404 Cygni, which consists of a dynamic duo of stellar objects: a black hole and a Sun-like star. Together, the binary pair create this celestial target.

The stellar structure is the result of a black hole eruption so powerful that it skipped the low-energy, visible spectrum of light and emitted high-energy X-ray light. Oddly, the black hole appears to have emitted three rather distinct rings of X-rays, but the truth is actually quite different. The beams of light are all from the same source.


You might think of black holes as being sky "sinkholes" that only suck matter in, as even light can't escape their gravitational clutches. So how could X-rays escape this one's grasp? 

The answer is in the accretion disk around the black hole. The black hole is in a binary system with its Sun-like star and as they circle each other in their celestial dance, the black hole's powerful gravitational attraction occasionally sucks up some of the star's outer layers of dust and gas. 

This stolen star matter swirls around the black hole in an accretion disk before being sucked into it. As the matter swirls around the disk, it gets faster and creates friction against the other dust particles, causing the disk to heat up. Eventually, the dust becomes so hot that it releases some of its energy in a dramatic X-ray burst. 

Based on the gif, you might think that the accretion disk releases three rapid-fire X-ray bursts. Astrophysicists, however, think that there's a simpler theory. A dust cloud between the black hole and the satellite that saw it would distort the X-ray burst, refocusing some of the light that was going to miss the photographing satellite back towards it. This distorted beam of light appears, from Earth, to be an entirely separate ring from the original X-ray burst.


Diagram shows how each ring is caused by X-rays bouncing off different dust clouds. Sebastian Heinz/University of Wisconsin-Madison.

Since there are three rings, there must be three clouds of dust between us and the black hole. The largest ring is estimated to be roughly a third of the diameter of the Moon.

These images of cosmic rings are some of the best examples of diffracted rays forming rings ever taken. They were snapped by NASA's Swift satellite, which specializes in photographing high-energy wavelengths of light like X-rays and gamma-rays. "The flexible planning of Swift observations has given us the best dust-scattered X-ray ring images ever seen," Andrew Beardmore, from the University of Leicestersaid. "With these observations we can make a detailed study of the normally invisible interstellar dust in the direction of this black hole."

Central GIF: Three X-ray rings spreading out from the black hole epicenter. NASA.


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