Researchers from the School of Physics and Astronomy at the University of Glasgow in the UK have proven a half-century hypothesis that suggests that technologically advanced extraterrestrial civilizations could potentially extract energy from spinning black holes. An article by researchers is published in the journal Nature Physics.
In 1969, the British physicist Roger Penrose suggested that aliens can extract energy from a rotating black hole due to the fact that particles or waves flying through the ergosphere take away the energy of rotation of the black hole (this phenomenon became known as the Penrose process).
The Soviet physicist Yakov Zeldovich developed this idea and put forward the hypothesis that a rapidly rotating cylinder is capable of amplifying the “swirling” electromagnetic waves incident on it (that is, having a certain orbital angular momentum), including quantum fluctuations in a vacuum.
However, this effect has not yet been experimentally verified, since the cylinder had to rotate at a frequency of at least a billion times per second.
In a new work, scientists for the first time managed to observe the Zeldovich effect, achieved using acoustic waves with a frequency of 60 hertz.
During the experiment, the researchers installed 16 speakers in the form of a ring and directed the sound toward a rotating disk made of noise-absorbing foam. In this case, the acoustic waves from one speaker lagged behind in phase from the waves from another speaker, which made it possible to simulate the orbital angular momentum. Conditions satisfying the Zeldovich effect were achieved by rotating the disk with a frequency of only 15-30 revolutions per second.
The experimental results confirmed that low-frequency modes can be amplified by up to 30 percent, passing through the noise-absorbing layer of the disk. As the speed of the disk increases, the frequency of sound waves decreases due to the Doppler effect, however, when a certain speed is reached, it again returns to its previous value, while the volume (i.e. the amplitude) increases. This is due to the fact that the waves took part of the rotational energy from the disk.
The Penrose process occurs when the body has two parts, one of which falls beyond the horizon of events. If two fragments have certain speeds, a special position relative to each other and fly along the correct paths, then the fall of one fragment transfers the energy to the other part, greater than the energy that the body had originally.
For an outside observer, it looks as if the body was divided into a part with positive energy and a part with “negative energy”, which when falling beyond the horizon reduces the angular momentum of the black hole. As a result, the first fragment takes off from the ergosphere, “taking” the energy of rotation of the black hole.
