In 1974, Stephen Hawking theorized that the universe's darkest gravitational behemoths, black holes, were not the pitch-black star swallowers astronomers imagined, but they spontaneously emitted light — a phenomenon now dubbed Hawking radiation.
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The problem is, no astronomer has ever observed Hawking's mysterious radiation, and because it is predicted to be very dim, they may never will. Which is why scientists today are creating their own black holes.
Researchers at the Technion-Israel Institute of Technology did just that. They created a black hole analog out of a few thousand atoms. 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, told Phys.org. "Hawking suggested that black holes are just like regular stars, which radiate a certain type of radiation all the time, constantly. That's what we wanted to confirm in our study, and we did."
The event horizon
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. To escape this boundary, a particle would have to break the laws of physics and travel faster than the speed of light.
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."
As explained by Heisenberg's uncertainty principle, even the complete vacuum of space is teeming with pairs of 'virtual' particles that pop in and out of existence. These fleeting particles with opposite energies usually annihilate each other almost immediately. 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. From this alone, given enough time (much longer than the age of the universe), a black hole could completely evaporate away.
"Hawking's theory was revolutionary because he combined the physics of quantum field theory with general relativity," Einstein's theory that describes how matter warps space-time,Steinhauer told Live Science. "It's still helping people to look for new laws of physics by studying the combination of these two theories in a physical example. 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."
This problem inspired Steinhauer and his colleagues to create their own black hole — a safer and much smaller one than the real deal.
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Source: https://www.livescience.com/black-hole-analog-confirms-hawking.html