Magazine article Science News

Hawking Radiation Created in the Lab: Sonic Black Hole Emits Energy as Famed Physicist Predicted

Magazine article Science News

Hawking Radiation Created in the Lab: Sonic Black Hole Emits Energy as Famed Physicist Predicted

Article excerpt

A whisper from a lab-manufactured black hole may confirm the existence of radiation predicted by physicist Stephen Hawking four decades ago. If validated by further research, the finding would offer evidence that particles blinking in and out of existence can rob black holes of mass.

"It's amazing, groundbreaking work," says physicist Daniele Faccio of Heriot-Watt University in Edinburgh. By observing Hawking radiation, the work "demonstrates something that everyone thought was impossible."

Initially, scientists thought of black holes as everlasting objects from which nothing, not even light, could escape. But in the mid-1970s, Hawking proposed an amendment to that rule with huge implications. He noted that quantum mechanics allows pairs of particles to spontaneously pop into existence in the vacuum of space. Usually those particles quickly annihilate each other. But if they formed at the event horizon--the black hole's point of no return--then one particle could get dragged in, while the other could escape as energy called Hawking radiation. The fleeing particle would take a small fraction of the black hole's mass with it, meaning that in the very far future, every black hole in the universe would evaporate.

After initially expressing skepticism, physicists have largely embraced the idea of Hawking radiation, and today it lies at the heart of the quest to unify general relativity, the theory that explains the very large stuff in the universe, and quantum mechanics, which dictates the very small (SN: 5/31/14, p. 16). Yet confirming Hawking's prediction is a tremendous challenge: The radiation emitted by black holes light-years away is almost certainly too feeble for detection by telescope.

Instead of looking for Hawking radiation in nature's black holes, physicist Jeff Steinhauer of Technion-Israel Institute of Technology in Haifa conducted the search on a homemade black hole that traps sound rather than light. He used lasers to cool a vat of rubidium atoms to temperatures about a billionth of a degree above absolute zero. Then he set those supercooled atoms, known as a Bose-Einstein condensate, in motion, creating a raging river of rubidium. The event horizon of Steinhauer's hole of silence emerged at the point where the rubidium's flow rate broke the sound barrier: Any sound waves emitted beyond that spot could not escape upstream (SN: 12/18/10, p. 28).

The success of Steinhauer's experiment hinged on observing pairs of sound waves that emerge from the vacuum at the event horizon. They would form via quantum fluctuations analogous to those predicted by Hawking to produce radiation around a real black hole. To make this acoustic Hawking radiation easier to detect, Steinhauer tried out a previously proposed strategy to make the radiation proliferate. …

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