Testing A Black Hole Property In The Lab

The analogue black hole. University of Nottingham

We can’t create a black hole in the lab (yet), but researchers at the University of Nottingham have done the next best thing and created a physical simulation of one. By using a sophisticated set-up, the team was able to create a “water black hole” and demonstrate experimentally the phenomenon of superradiance. The study is published in Nature Physics.

“This research has been particularly exciting to work on as it has brought together the expertise of physicists, engineers, and technicians to achieve our common aim of simulating the conditions of a black hole and proving that superradiance exists,” team leader Dr. Silke Weinfurtner said in a statement. “We believe our results will motivate further research on the observation of superradiance in astrophysics.”

Superradiance is a very interesting property of black holes. When a wave approaches a black hole, it can either be captured and fall in or it can swing around it, stealing some of the black hole's energy. This is the physical phenomenon behind the Penrose mechanism, which is a theoretical way to get energy out of a black hole.

Superradiance is seen as a precursor of Hawking radiation, although the latter is a quantum mechanical effect rather than a consequence of general relativity.

“Some of the bizarre black hole phenomena are hard, if not, impossible to study directly," Dr Weinfurtner added. "This means there are very limited experimental possibilities. So this research is quite an achievement."

This is not the first attempt at creating experimental models of black holes. Over the last decade, Professor Jeff Steinhauer from the Israel Institute of Technology used sound to create black holes that can be tested. In this case, the scientists went another route.

“This research has grown from humble beginnings. I had the initial idea for a water based experiment when I was at the International School for Advanced Studies (SISSA) in Italy and I set up an experiment with a bucket and a bidet,” Dr Weinfurtner recalled. “However, when it caused a flood I was quickly found a lab to work in!”

The experimental water-bath system is specially designed to accommodate 2,250 liters (595 gallons) of water. It’s a closed water system with a plug in the middle, where the water is drained creating the analogous of a black hole. Then a mechanical system produces waves until they reach the specific frequencies to create superradiance.

The effects of superradiance were then studied with an ad-hoc sensor that can produce 3D images of the surface between air and water. The researchers witnessed a maximum amplification of the waves by 14 percent, which is well within the allowed range based on theory. 

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