KEY POINTS

• The Penrose experiment was introduced about 50 years ago
• Researchers simulated the conditions of a black hole for a new study
• The study proved that objects can escape black holes with additional energy

An experiment proposed about 50 years ago has finally able to prove that energy can be extracted from a black hole. The discovery was made after researchers simulated the conditions of a rotating black hole.

The Penrose experiment is a theoretical process introduced by mathematical physicist Roger Penrose in 1969. It focuses on a region surrounding a black hole known as the ergosphere, which is just outside the event horizon.

In black holes, the event horizon is the region where the gravitational pull is at its strongest. Located beyond the event horizon is a region where space-time gets twisted as it gets dragged into the black hole. This effect, known as frame-dragging, occurs within the ergosphere.

According to Penrose’s calculations, objects within the ergosphere can sometimes escape the pull of the event horizon and get flung out into space. As it gets kicked out, the object gains additional energy from the event horizon. Penrose estimated that the objects that are able to escape gain about 21% more energy.

Recently, physicists from the University of Glasgow’s School of Physics and Astronomy in Scotland conducted a new study based on Penrose’s experiment. To see if objects ejected from the event horizon carry additional energy, the researchers simulated the conditions of a black hole.

Their model consisted of a ring of speakers installed around a rotating sound absorber made out of a foam disc. The absorber represented the center of the black hole, while the speakers twisted the sound waves to simulate the effect of the event horizon.

Microphones were then placed on both sides of the absorber to detect the sound waves passing through the foam disc. If the pitch and amplitude of the sound waves changed as they go through the disc, then this would mean that they are leaving the model with additional energy, just like in Penrose’s theory.

“The twisted sound waves change their pitch when measured from the point of view of the rotating surface,” Marion Cromb, the lead author of the study, said in a statement. “If the surface rotates fast enough then the sound frequency can do something very strange - it can go from a positive frequency to a negative one, and in doing so steal some energy from the rotation of the surface.”

After carrying out the experiment, the researchers detected a significant change in the pitch of the sound waves. They noted that the sound waves became 30 percent louder, indicating that they were picking up additional energy.

In actual black holes, the additional energy within the objects escaping from the event horizon can be extracted. But before this can be done, humans still have to figure out a way to safely approach a black hole.

“We're thrilled to have been able to experimentally verify some extremely odd physics a half-century after the theory was first proposed,” Daniel Faccio, the study’s co-author, stated. “It's strange to think that we've been able to confirm a half-century-old theory with cosmic origins here in our lab in the west of Scotland, but we think it will open up a lot of new avenues of scientific exploration.”

The results of the experiment conducted by the researchers were presented in a new study published in the journal Nature Physics.