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  1. What We Study
  2. Into a Black Hole - Stephen Hawking
  3. Sorry, Black Holes Aren't Actually Black

But a prediction made by Albert Einstein in his theory of general relativity stated that under certain circumstances, an outline of a black hole and its light-swallowing event horizon could be seen, according to representatives of the Haystack Observatory at MIT, which houses one of the EHT telescopes. In the image, the dark circle represents the "shadow" of the black hole and its boundary, created by the glowing material that surrounds it. However, the colors of the bright ring in the image aren't the actual hues of the gas; rather, they represent a color map chosen by EHT researchers to depict the brightness of the emissions, Fox explained.

What We Study

In the optical range, the ring around the black hole would likely appear white, perhaps tinged with blue or red, according to Fox. Hawking proposed that when virtual pairs pop into existence near a black hole, though, they're torn apart by the pull of the black hole, with the antimatter being sucked in while the matter shoots off into space — at this point, they're no longer virtual, but real, particles.

The negative charge belonging to the antimatter particles reduces the energy and mass of the black hole that's absorbed it by a tiny amount — however, when a black hole ingests enough of these, it evaporates. The positively charged particles fly away as what's now called "Hawking radiation. Hawking also predicted that the radiation emitted would exhibit a continuous thermal spectrum rather than discreet light wavelengths preferred by individual escaping photons. The temperature of the spectrum would be determined instead by the black hole's mass.

Part of the problem in testing Hawking's theories was summarized by physicist Silke Weinfurtner, who has written :. And for the smallest observed black holes, which have a mass similar to that of the Sun, this temperature is about 60 nanokelvin.

Into a Black Hole - Stephen Hawking

Hawking radiation therefore produces a tiny signal, and it would seem that the phenomenon cannot be verified through observation. Experimental physicist Jeff Steinhauer of Technion—Israel Institute of Technology in Haifa, Israel, has been working alone in his lab for years creating sonic "black holes" that suck in and trap sound waves. He's a drummer, too. Physicist William Unruh of the University of British Columbia in Vancouver, Canada, first proposed the creation of a sound-wave black-hole replica in as a safe way of observing the behavior of the stellar version. Steinhauer's black-hole replica was "constructed" within a Bose-Einstein condensate BEC , an extremely strange form of matter in which atoms are cooled to a temperature vanishingly close to absolute zero.

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At this temperature, there's so little energy available that atoms barely move at all in relation to each other, and thus the entire superfluid begins to behave as one big, unified atom. Within such a frigid condensate, weak quantum fluctuations occur, and these produce pairs of entangled phonons , compressional waves that can create the air-pressure changes we perceive as sound. Working with a cigar-shaped trap just a few millimeters long, Steinhauer cooled some 8, iridium atoms into a BEC. Inside it, the speed of sound, the rate at which the condensate flowed, dropped from meters per second to an almost stationary half a millimeter per second.

Reducing the density of one area of the BEC to allow atoms to travel at 1 millimeter per second, though he created a supersonic region — at least compared to the lower speed in the rest of the condensate, that is. Its comparatively rapid current overwhelmed and pulled in any high-energy phonons that came near its event horizon, thus trapping them.

Sorry, Black Holes Aren't Actually Black

In August, Steinhauer published a paper in Nature that documented his observation of phonons emerging from his artificial black hole in line with Hawking's predictions. Sometimes, as matter is drawn toward a black hole, it ricochets off the event horizon and is hurled outward, rather than being tugged into the maw. Bright jets of material traveling at near-relativistic speeds are created. Although the black hole remains unseen, these powerful jets can be viewed from great distances. The Event Horizon Telescope's image of a black hole in M87 released in was an extraordinary effort, requiring two years of research even after the images were taken.

That's because the collaboration of telescopes, which stretches across many observatories worldwide, produces an astounding amount of data that is too large to transfer by internet. With time, researchers expect to image other black holes and build up a repository of what the objects look like. The Event Horizon Telescope, a planet-scale array of eight ground-based radio telescopes forged through international collaboration, captured this image of the supermassive black hole in the center of the galaxy M87 and its shadow. LIGO's observations also provide insights about the direction a black hole spins.

As two black holes spiral around one another, they can spin in the same direction or in the opposite direction. There are two theories on how binary black holes form. The first suggests that the two black holes in a binary form at about the same time, from two stars that were born together and died explosively at about the same time. The companion stars would have had the same spin orientation as one another, so the two black holes left behind would as well.

Under the second model, black holes in a stellar cluster sink to the center of the cluster and pair up. These companions would have random spin orientations compared to one another. This article was updated on July 11, by Space.

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