A laboratory-created analogue of a black hole has provided new circumstantial evidence that these mysterious cosmic objects do emit gas streams of charged particles, Science Alert reports, citing a new scientific study published in the journal Nature. Physicists claim that the analogue of a black hole they created has a temperature, which is a prerequisite for the radiation of the same name, predicted by Stephen Hawking.
Black holes emit nothing. Or does it radiate?
According to general relativity (GR), nothing can escape a black hole. Their gravitational force is so great that even light, the fastest thing in the Universe, is not able to develop sufficient speed to break out of its influence. Thus, according to general relativity, black holes cannot emit any kind of electromagnetic radiation.
Nevertheless, Hawking's 1974 theory suggested that if the rules of quantum mechanics were added to the question, then black holes could indeed emit something. It is a theoretical type of electromagnetic radiation named after Hawking himself.
This hypothetical radiation resembles black body radiation generated by the temperature of a black hole, which is inversely proportional to its mass. Scientists have not yet been able to find it directly. The first real pictures of the black hole were recently taken, so everything is still ahead. Nevertheless, physicists believe that this radiation, if it exists, would be too weak to be found with our modern scientific instruments.
Measuring the temperature of a black hole is also challenging. A black hole with the mass of the Sun will have a temperature of only 60 nanokelvin. The cosmic microwave background radiation it will absorb will be much higher than the Hawking radiation it would emit. Moreover, the larger the size of the black hole, the lower its temperature will be.
To test Hawking's hypothesis, physicists from the Israel Technical University conducted an experiment with the closest "analogue" of a black hole, which has been successfully created in the laboratory.
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Is Hawking radiation real?
It was invented by Israeli physicist Jeff Steinhower in 2016 and is a Bose condensate of cold rubidium atoms (cooled to near absolute zero), in one of which the atoms move at supersonic speed, and in the other they move very slowly. As it moves, the condensate creates a so-called acoustic black hole, which traps sound (phonons) instead of light (photons). The quanta of sound entering this area cross a kind of "acoustic event horizon", since they can no longer leave it. Studying the characteristics of the acoustic analogue of a black hole, experts came to the conclusion that they were close to theoretical models implying the presence of Hawking radiation.
Even during the experiment in 2016, Steinhower and his colleagues were able to demonstrate that in the region of the acoustic event horizon of their analogue of a black hole, a pair of entangled phonons can arise, one of which is repelled from it by atoms of a slowly flowing Bose condensate into space, creating in fact the Hawking radiation effect. At the same time, another phonon of a pair can be absorbed by an analogue of a black hole due to a high-speed condensate.
It should be noted that earlier this year, another group of Israeli physicists from the Weizmann Institute, led by Ulf Leonhardt, created their own analogue of a black hole, which used fiber optic technology as a base for the event horizon. Then the scientists considered a similar observed result to be a statistical anomaly. However, a new experiment by Steinhauer's group proved that this is not the case. The result of the new experiment showed once again that one photon can be thrown into hypothetical space, while another can be absorbed by a hypothetical black hole. Leonhardt has already commented on the success of the Steinhower group:
Evidence that Hawking was right is growing, but this new method for determining the temperature of an analog black hole could help gain a deeper understanding of the thermodynamics of a black hole.
Nikolay Khizhnyak