Humans have been scanning the cosmos for decades now in hopes of discovering the existence of an intelligent alien civilization. So far, no positive results have yet been able to confirm the presence of the aliens, research being based on the detection of radio waves that the aliens could emit. A recent study could offer another avenue to explore for alien hunters , it is to identify the traces that the latter could leave when they exploit the energy coming from black holes.
According to the scientists behind the study, a technology capable of harvesting energy from a rotating black hole could leave traces just outside the event horizon. This process could thus be at the origin of certain shards of plasma that researchers have already detected near these cosmic objects. The article published on January 13 in the journal Physical Review D in fact proposes a new way of obtaining energy from black holes, a method that may be exploited by possible extraterrestrial civilizations.
According to astrophysicist Luca Comisso of Columbia University in New York and co-author of the study, they were only able to establish the physics behind the new method of extracting energy from black holes. Now what remains to be done is to determine what kind of signal one should look for to say that the process is taking place somewhere in the Universe.
The principle behind the new theory
This isn't the first time scientists have come up with a way to harness the energy produced by rotating black holes. This latest study is in fact the fourth to do so in 50 years.
From what is known, the best-known theory is that established by the physicist Roger Penrose in 1969. The latter proposed a process, today known as the Penrose Process, which involves a particle se dividing in half near a black hole spinning at almost the speed of light. One part of the particle will then fall through the ergosphere, which is the region just outside the event horizon, and end up inside the black hole. Calculations indicate that objects falling into the ergosphere can have negative energy, a phenomenon that is only possible in this precise area.
Physics dictates that when you add a particle with negative energy to a black hole, it is equivalent to extracting energy from it. So, if an advanced civilization could capture the part of the particle that escaped from the black hole, that would be one way to get energy.
The difference between Penrose's theory and that of the new study is that Penrose just considered a single particle dividing into two. The recent study considers astronomical quantities of plasmas generated in the accretion disk around the black hole. Plasmas are indeed made up of a large number of particles, which means that a very large amount of energy could be extracted.
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The origin of plasmas
Plasmas that can be used for energy have a particular origin, as explained by Comisso and Felipe Asenjo, the latter being an astrophysicist from the Universidad Adolfo Ibanez de Santiago in Chile, and co-author of the article . These plasmas would be created from “magnetic reconnection” events. During this process, strong magnetic field lines become entangled, broken, and joined, and this is happening just outside the event horizon.
Magnetic reconnections are usually seen on the surface of stars like the Sun. When the plasma jets created on the stars from this phenomenon are created, they fall directly back into the star or are ejected into space. In the case of a rotating black hole, a plasma jet which falls back through the ergosphere could have negative energy, while the escaping jet will obtain additional energy.
In any case, even if this theory is correct, there is still a very long way to go before we can one day take advantage of the energy produced by black holes. In the meantime, it is still possible to scan the sky to see if any extraterrestrial civilizations may have had the same idea.