How a black hole condenses

Artificial black hole in the laboratory : Researchers detect Hawking radiation

A common assumption is that nothing can escape the enormous gravitational force of black holes. Not true, contradicted the British astrophysicist Stephen Hawking in 1974. They give off weak heat radiation, which means that black holes are not completely black and, on the other hand, lose mass and can therefore dissolve over a long period of time. However, this "Hawking radiation" is so weak that it has not yet been detected - until now.

Everything disappears behind the event horizon

A team led by Jeff Steinhauer from the Technion - Israel Institute of Technology in Haifa has succeeded in creating an "artificial" black hole in the laboratory. As they report in the specialist magazine “Nature”, they used it to measure the thermal radiation that Hawking's predictions and thus his theory correspond to.

The physicist's considerations are based on the fact that the vacuum is not completely empty. Rather, pairs of virtual particles and anti-particles are constantly emerging, which immediately cancel each other out again. It gets exciting at the event horizon, the zone that surrounds every black hole and behind which everything disappears irretrievably in the hole.

If a virtual pair of particles emerges on the event horizon, one partner can fall into the black hole while the other remains. According to the theory, the remaining particle forms Hawking radiation. The particle that falls into the black hole has negative energy. Put this into Einstein's formula E = mc2, it follows that the mass of the black hole decreases. However, this happens so slowly that this effect cannot be observed in real black holes.

The acoustic equivalent is evidence of radiation

For a long time, researchers have been working on experiments to simulate black holes in the laboratory. Jeff Steinhauer and his team have managed to build an acoustic equivalent. It consists of around 8,000 rubidium atoms that form a Bose-Einstein condensate. This means that they are cooled down so extremely that they reach a special physical state in which all atoms have the same physical properties for a short time.

With the help of a laser, the scientists created a zone in it that moves at supersonic speed, while the rest of it flows at subsonic speed. The transition of both zones corresponds to the event horizon. According to the researchers, pairs of sound waves are formed there. While one wave disappears in the black hole, the other moves away from the supersonic zone and forms radiation with a temperature of only 0.351 nanokelvin - as weak as Hawking predicted.

Hawking temperature determined using quantum simulation

"The finding establishes a connection between the theories of Stephen Hawking and Jacob Bekenstein," explains Jeff Steinhauer in an email. “Interestingly, they both concluded that the temperature should be determined by gravity on the surface of the black hole, but their calculations were based on very different ideas. The measurement confirms that this is actually the relevant temperature. "

In an accompanying commentary in “Nature”, Silke Weinfurtner from the University of Nottingham acknowledges the achievement of the Technion team, who for the first time succeeded in determining the Hawking temperature using quantum simulation. The experimental arrangement is promising and could help to research further phenomena.

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