They were trying to confirm two of Hawking's most important predictions, that Hawking radiation arises from nothing and that it does not change in intensity over time, meaning it's stationary.
"A black hole is supposed to radiate like a black body, which is essentially a warm object that emits a constant infrared radiation," study co-author Jeff Steinhauer, an associate professor of physics at Technion-Israel Institute of Technology, said in a statement."Hawking suggested that black holes are just like regular stars, which radiate a certain type of radiation all the time, constantly.
The gravity of a black hole is so powerful that not even light can escape its grasp, once a photon, or light particle, crosses beyond its point-of-no-return, called the  event horizon.Hawking showed that although nothing that crosses the event horizon can escape, black holes can still spontaneously emit light from the boundary, thanks to quantum mechanics and something called "virtual particles." .But due to the extreme gravitational pull at an event horizon, Hawking suggested pairs of photons could be separated, with one particle getting absorbed by the black hole and the other escaping into space.
The absorbed photon has negative energy and subtracts energy in the form of mass from the black hole, while the escaped photon becomes Hawking radiation?
People would like to verify this quantum radiation, but it's very difficult with a real black hole because Hawking radiation is so weak compared to the background radiation of space.".
Using a second laser beam, the team created a cliff of potential energy, which caused the gas to flow like water rushing down a waterfall, thereby creating an event horizon where one half of the gas was flowing faster than the speed of sound, the other half slower.[That's] just like being in a black hole, once you're inside, it's impossible to reach the horizon.".
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