Physicists have created an analogue of a black hole and confirmed Hawking's theo

Posted by Foret Horet on April 15th, 2021

Scientists at the Israel Institute of Technology have created a sound analogue of a black hole in the laboratory, confirming the existence of stable Hawking radiation. Earlier, physicists from Mexico and Israel first demonstrated the existence of Hawking radiation using ultrashort laser pulses and photonic crystal fibers. However, it has not been possible to confirm the stability of the radiation so far. We will tell you what it is, how scientists have created an analogue of a black hole and what the new discovery will lead to.

How do black holes "work"?

Black holes are regions in space where gravity is very strong. Moreover, it is so strong that everything that falls into them cannot "escape" - not even the light. Theoretical predictions suggest that there is a radius around black holes known as the event horizon. Once something crosses it, it can no longer leave the black hole. The point is that gravity gets stronger as you get closer to its center.

In an ordinary black hole, Hawking radiation appears when a pair of virtual particles appears at the event horizon, which turns into a particle-antiparticle pair. In this case, one particle falls over the horizon, and the other flies away.

What did Hawking predict?

Theoretical physicist Stephen Hawking predicted that although nothing can leave black holes, they themselves spontaneously emit a limited amount of light. It is known as Hawking radiation. According to the predictions of the physicist, this radiation is spontaneous (that is, it arises from nothing) and stationary (that is, its intensity does not change much over time).

Hawking radiation is the main argument of scientists regarding the decay (evaporation) of small black holes, which theoretically can arise during experiments at the LHC - the Large Hadron Collider. This effect is based on the idea of ​​a singular reactor - a device for obtaining energy from a black hole using Hawking radiation.

V. Gribov, in a discussion with Ya. Zel'dovich, insisted that due to quantum tunneling, black holes should emit particles. Even before the publication of his work, Hawking visited Moscow in 1973, where he met with Soviet scientists Yakov Zeldovich and Alexei Starobinsky. They demonstrated to Hawking that, according to the uncertainty principle of quantum mechanics, rotating black holes should generate and emit particles.

According to Hawking's predictions, emission from black holes is spontaneous. In their new study, the scientists set out to find out whether the radiation emitted by their black hole is also stationary (i.e., whether it remains constant over time).

What did the scientists find out?

Researchers at the Technion Israel Institute of Technology recently conducted research aimed at testing Hawking's theoretical predictions. In particular, they investigated whether the equivalent of Hawking radiation in a laboratory-created "artificial black hole" was stationary.

If you go inside the event horizon, you will not be able to get out of here, even for light. Hawking's radiation begins just below the event horizon, from where light can barely escape. This is really strange because there is nothing there; this is empty space. But this radiation starts from nothing, goes out and goes to the Earth.

How did scientists create an artificial black hole?
The man-made black hole, created by Israeli scientists, was approximately 0.1 mm long and was made from a gas composed of 8,000 rubidium atoms. This is a relatively small number of atoms. Every time the researchers photographed it, the black hole collapsed. Thus, in order to observe its evolution over time, they had to create a black hole, photograph it, and then create another one. This process was repeated many times over the course of months.

Hawking radiation from this analogous black hole is made up of sound waves, not light. Rubidium atoms move faster than the speed of sound, so sound waves cannot reach the event horizon and escape from the black hole. However, outside the event horizon, gas flows slowly, so sound waves can move freely.

Rubidium flows quickly, faster than the speed of sound, which means that sound cannot go against the flow. Let's say a person is trying to swim against the current. If this current goes faster than he is able to swim, then it is simply impossible to move forward. The swimmer is constantly pushed back - the stream moves too fast and in the opposite direction. As a result, a person gets stuck in one place. This is what it is like to be stuck in a black hole and try to reach the event horizon from within.

Hawking radiation consists of pairs of photons (that is, light particles): one comes out of the black hole and the other falls back into it. In an effort to identify Hawking radiation emitted by an analog black hole, scientists looked for similar pairs of sound waves, one emerging from the black hole and the other moving into it. After they identified these pairs of sound waves, the researchers tried to determine if there were correlations between them. Physicists repeated their experiment 97,000 times - that's 124 days of continuous measurements. As a result, the researchers found that the analogue of the black hole has a pair of sound waves, and also confirmed the correlation between them.

Overall, the results seem to confirm that the radiation emitted by black holes is stationary, as Hawking predicted. While these results relate primarily to the analogue black hole they created, theoretical studies can help confirm whether they can be applied to real black holes as well.