Experiments made with a black hole created in the laboratory by researchers at the Technion-Israel Institute of Technology, helped to prove a theory physicist Stephen Hawking proposed 47 years ago, regarding the spontaneous emission of light by these mysterious celestial objects. The research is detailed in an article recently published in Nature Physics.
The famous British scientist theorized, in 1974, that black holes were not just giant star swallowers as astronomers thought. Hawking said they also had the ability to emit light spontaneously, a phenomenon called “Hawking radiation” in his honor.
“If you go inside the event horizon, there’s no way to get out, even for light,” said Jeff Steinhauer to Phys.org, Physics Professor at the Technion-Israel Institute of Technology who co-authored the study. “Hawking radiation starts just outside the event horizon, where light can barely escape. That is really weird because there’s nothing there; it’s empty space. Yet this radiation starts from nothing, comes out, and goes towards Earth.”
Proving such a theory has always been a complicated task, since observing the supposed light emitted by the celestial bodies, considered weak to be viewed from a distance, was unlikely. Thus, the alternative was to build an artificial black hole.
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To do this, the scientists used a gas flowing from approximately 8,000 rubidium atoms cooled to almost absolute zero, in addition, a laser beam was used to keep it in place. From there, a mysterious state of matter known as Bose-Einstein Condensate (BEC) was created, in which thousands of atoms can act as if they were one.
In the sequence, the use of a second laser allowed the creation of a peak of potential energy, where half of the gas flowed faster than the speed of sound and the other half more slowly. In this experiment, they found pairs of quantum sound waves known as phonons, forming spontaneously in the gas.
The next step was to confirm that the pairs of phonons were correlated (in the slowest half, a phonon traveled against the gas flow, while the fastest one was trapped) and that Hawking radiation was stationary, remaining constant throughout the time.
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But to carry out this confirmation and prove the theory of the deceased physicist, the team repeated the experiment no less than 97 thousand times, during 124 days of continuous measurements, which paid off in the end.
“A black hole is supposed to radiate like a black body, which is essentially a warm object that emits a constant infrared radiation. 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.” said Steinhauer.
