Extract from the energy of a cosmic monster?
The story begins in 1969 with Roger Penrose, future Nobel Prize, which imagines a theoretical process called since … The Penrose process. In this idea, an object sent to the ergosphere – the region just outside the horizon of a black hole in rotation – could be split. A part would fall into the black hole with negative energy, and the other would come out with more energy than it had at the start. Result: the black hole would lose a little of its energy mass, as if it had been stolen from it a tiny portion of its rotation.
Zel'dovich and the shadow of a black hole on earth
But it was the physicist Yakov Zel'dovich who, a few years later, proposed a more “achievable” version of the phenomenon. According to him, if a wave (sound or electromagnetic) with an angular moment strikes an object turning at high speed, it can come out amplified – as if it had captured part of the rotation of the object. This phenomenon, known as superradiance, would become observable without the need for a real black hole.
Problem: this idea remained, until recently, confined to the pages of theoretical newspapers. Too difficult to test in practice. Until today.
The experience that changes the situation
Physicists have finally managed to reproduce this phenomenon in the laboratory, with remarkable ingenuity. The heart of their experience? An aluminum cylinder put into mechanical rotation. On this object, scientists have directed twisted electromagnetic waves, that is to say waves which, like a luminous corkscrew, transport an angular moment.
Two crucial parameters were accurately adjusted:
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A speed of rotation sufficiently high for the frequency of waves, perceived from the cylinder, becomes negative (what is called a rotational doppler offset).
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A resonator system attached to the cylinder, making it possible to trap and amplify the waves if they receive an energy boost.
Result: under certain conditions, the waves came out of the more energetic system than they were when entering. In other words, they had stolen part of the rotation of the cylinder. It is the very first experimental demonstration of the Zel'Dovich effect with electromagnetic waves.
A black hole bomb, table version
Building on this success, the team pushed the experience further, by building a analog of the famous “black hole bomb”, a concept proposed in the 1970s by William Press and Saul Teukolsky. In this version, the amplified wave is returned to the object in rotation to be amplified again … and again, and again. Result: exponential instability occurs, with an unleashing of waves generated from ambient noise.
This device obviously does not create black holes, but it spectacularly illustrates how a rotating system can be emptied of its energy to feed a wave, which is reinforced with each passage.
© Buradaki/Istock
Illustration of a (real) black hole
A demonstration, and promises
Why is this experience so important? First, because it experimentally validates a theoretical prediction of half a century old. Then, because it confirms that processes similar to those of black holes can be studied under laboratory conditions. It is a spotlight on the effects of superradiance, which could play a much more important role than we thought in the real universe.
Because if the Zel'Dovich effect is active in space, it could amplify certain waves – gravitational or electromagnetic – near black holes. This would change the way in which we understand the energetic dynamics of these extreme objects, and perhaps open new indirect observation windows for astrophysicists.
(Very) terrestrial applications
Beyond the implications for cosmology, this phenomenon could have very concrete benefits. By finely controlling the amplification of waves by a rotation object, one could imagine:
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generators of ultra-effective electromagnetic or acoustic waves,
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mechanical energy recovery systems,
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Ultra-sensitive radars or communications, capable of detecting tiny signals thanks to an amplification effect based on rotation.
The concept of “recycling” an energy otherwise lost in a rotation could thus find industrial outlets, even if these applications remain speculative for the moment.
A door ajar towards a deeper physique
For researchers, the objective is now double: refine their models to better simulate these effects in a cosmic context, and explore new experimental configurations, with different materials, forms or wave diets. The idea is to understand how this energy transfer works in its smallest detail, for one day, perhaps, to take full advantage of it.
The Zel'Dovich effect is no longer a simple theoretical curiosity. It is now a real, measurable, usable phenomenon. And as often in physics, this kind of breakthrough opens doors … to the unknown.
Source: Arxiv
With an unwavering passion for local news, Christopher leads our editorial team with integrity and dedication. With over 20 years’ experience, he is the backbone of Wouldsayso, ensuring that we stay true to our mission to inform.
