Fifty years ago, the English mathematical physicist and Nobel Prize winner Roger Penrose suggested extracting energy from space around a rotating black hole. This region, known as the ergosphere, lies just outside an event horizon, the limit within which nothing can escape the pull of a black hole (even light). Here also infallible matter is accelerated to unbelievable speeds and gives off all kinds of energy.
This became known as the Penrose process, which many theorists have since expanded upon. The latest comes from a study by researchers from Columbia University and Universidad Adolfo Ibáñez in Chile. With support from organizations like NASA, they showed how a better understanding of physics when working with spinning black holes could one day enable us to harness their energy.
The study, entitled “Magnetic Reconnection as a Mechanism for Generating Energy from Rotating Black Holes” was carried out by Luca Comisso and Felipe A. Asenjo. In it, they propose a new method for extracting energy from a black hole by breaking and rejoining magnetic field lines near its event horizon, the limit within which nothing can escape the gravitational pull of a black hole (even light).
The artist’s impression shows a rapidly rotating supermassive black hole surrounded by an accretion disk. Recognition:
As Comisso, a Columbia University scientist and the study’s first author, stated in a Columbia News press release:
“Black holes are usually surrounded by a hot ‘soup’ of plasma particles that carry a magnetic field. Our theory shows that magnetic field lines, when properly separated and reconnected, accelerate plasma particles to negative energies and large amounts of energy can be extracted from black holes. “
While Penrose theorized in 1971 that this process of particle decay could draw energy from a black hole, Stephen Hawking proposed in 1974 that black holes could release energy through quantum mechanical emission (known as Hawking radiation). It was followed by Roger Blandford and Roman Znajek, who suggested in 1977 that electromagnetic torque was the main means of generating energy.
For their study, Comisso and Senjo looked at an important part of the Penrose process, in which magnetic field lines break apart and reconnect near the event horizon. This causes infalling matter to transform into two streams of charged particles (also known as plasma), one of which is pushed against the spin of the black hole and absorbs negative mass energy, causing it to fall beyond the event horizon into the black hole.
Visualization of an ergosphere surrounding the event horizon of a black hole. Image credit: Visser. M. (2008)
In the meantime, the other plasma stream is driven in the same direction as the spin of the black hole, allowing it to absorb additional mass energy and escape into the ergosphere. Within the ergosphere, the reconnection of magnetic field lines is so extreme that the plasma particles are accelerated to speeds approaching the speed of light (also known as relativistic speeds).
This essentially means that a black hole loses energy by eating particles with negative mass energy. In addition, the high relative speed between trapped and exiting plasma streams enables the process in which enormous amounts of energy can be extracted from a black hole. As Asenjo, professor of physics at Universidad Adolfo Ibáñez and co-author of the study, explained:
“We have calculated that the process of plasma excitation can achieve an efficiency of 150 percent, much higher than any power plant on earth. An efficiency of more than 100 percent is possible because black holes lose energy, which is given free of charge to the plasma emerging from the black hole. “
While it sounds like science fiction, it’s entirely possible that future generations will be looking for black holes to meet their energy needs. In addition, according to Comisso and Asenjo, the process of generating energy could already take place with a series of black holes in the observable universe. This may be the reason for black hole flares, which are powerful bursts of radiation that can be detected from Earth.
The first image of an event horizon around a supermassive black hole (SMBH) captured by the Event Horizon Telescope (EHT). Photo credit: EHT Collaboration
“In thousands or millions of years, mankind could be able to survive around a black hole without using the energy of the stars,” Comisso said. “It’s essentially a technological problem. If we look at physics, there is nothing stopping it. “
In fact, it is possible that sufficiently advanced species in our universe are already using black holes for their limitless energy. One such scenario was recently discussed in an article by Marion Cromb, Ph.D. Astrophysics student in the Faculty of Physics and Astronomy at the University of Glasgow. It is also part of the Transcension Hypothesis, a proposed solution to the Fermi Paradox that Roger Smart originally proposed in 2002.
Smart was not only an ultimate source of energy, but also suggested that black holes would enable a “transcendent” (sophisticated) species to “have a computationally optimal domain of increasingly dense, productive, miniaturized and efficient scales of space, time and energy and Matter. “There’s even an opportunity to explore alternative physics models, time travel, and see the“ seeds ”of new universes!
There are also theories about how tiny black holes could be used to propel interstellar spacecraft (the black hole propulsion), or how an event horizon could become a propulsion means (the halo propulsion). This latter idea works much like a gravity-assist maneuver, in which a spaceship would use the event horizon of a spinning black hole to hurl itself at distant stars at a speed approaching the speed of light.
Photo credit: NASA / Goddard Media Studios
Meanwhile, studies like this one are part of a growing effort to expand our knowledge of black holes and the exotic physics around them. As Asenjo has indicated, theoretical studies of black hole physics are especially important at a time when global efforts like the Event Horizon Telescope (EHT) are enabling the first images of black holes to be captured:
“Our expanded knowledge of how magnetic reconnections occur near the black hole could be critical to our interpretation of current and future telescope observations of black holes such as those used by the Event Horizon Telescope.”
The study, recently published in the journal Physical Review D, was made possible thanks to funding from NASA, the Chilean National Fund for Scientific and Technological Development (FONDECYT), and the Windows on the Universe initiative from the National Science Foundation (NSF) . A synthesis program that brings theoretical physics and observational astronomy under one roof to answer some of the most profound questions.
Further reading: Columbia News, Physical Review D.