Thermal analog black hole in accordance with Hawking radiation theory

A team of researchers at the Israel Institute of Technology discovered that a thermal analog black hole they had created was in keeping with Hawking's theory of radiation. In their article published in the newspaper Nature, the group describes how to build its analogue black hole and use its data to test its temperature. Silke Weinfurtner of the University of Nottingham has published an article in News and Views on the work done by the team in the same issue of the journal.

One of Stephen Hawking's theories suggests that all materials that approach a black hole do not fall in – he argued that in some cases in which entangled particle pairs appear, a only one of them would fall, while the other escaped. The particles that escaped were called Hawking radiation. Hawking also predicted that radiation coming out of a black hole would be thermal and that its temperature would depend on the size of the black hole. It is difficult to test the theory because of the nature of the black holes – any radiation that comes out of it would be too weak to be observed. To solve this problem, researchers have been working on creating analogs of black holes in the lab. In this new effort, researchers have built one designed to absorb sound rather than light. With such an analog, pairs of phonons served as substitutes for entangled particles in a real black hole.

The experiment consisted in cooling a group of rubidium atoms and using lasers to create a Bose-Einstein condensate. The atoms were then forced to flow in a manner that resembled trapping that occurs with a real black hole. With such a flow, the sound waves were unable to escape under normal circumstances. In their experiment, the researchers were able to force one of a pair of phonons to fall into the flow of atoms while the other was allowed to escape. In doing so, the researchers measured both phonons, allowing them to estimate their temperature at 0.035 billionth of a Kelvin. And in doing so, they found that this was consistent with Hawking's prediction. They also agreed that the radiation of such a system would be thermal.

The work does not prove the theory, of course; the only way to achieve this will be to develop a technology that can actually measure the radiation of a real black hole – but this gives the theory more credibility.

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