Opava physicists study how to protect humankind from dangerous radiation of black holes and use it to our advantage

  • Tomáš Lanča
  • 01.03.2022
Supermassive black holes can be a good servant, but also a very evil lord for possible civilizations throughout the Galaxy. A new study by Opava physicists’ points to three types of energy production in the vicinity of black holes, ie three variants of the so-called Penrose process. Huge amounts of energy could be extracted from these processes in the future; however, the same processes can lead to the fatal escape of strong radiation and endanger the lives of any galaxy. Thus, physicists from Opava are studying not only the possibilities of using this gigantic source of energy, but also how to detect a possible energy leak and protect civilization.
A supermassive black hole surrounded by a disk of matter emits high-energy radiation through so-called jets. artistic illustration: ESO. A supermassive black hole surrounded by a disk of matter emits high-energy radiation through so-called jets. artistic illustration: ESO.
The so-called supermassive black holes, located in the middle of galaxies, store a gigantic amount of energy. A team of physicists from the Institute of Physics in Opava, prof. Zdeněk Stuchlík, Arman Tursunov and Martin kološ, describe the mechanisms of generating such energy. In their new scientific work, they focused on the consequences of the so-called Penrose processes, ie on the description of obtaining energy from the immediate vicinity of black holes. As early as 1969, the British physicist Roger Penrose (b. 1931), winner of the Nobel Prize in Physics in 2020, discovered that a vast amount of energy could be gained around a rotating black hole through a phenomenon known as "frame-dragging".

Huge amount of energy hidden in a magnetic field

In 1977, physicists Roger Blandford and Roman Znajek came up with the theory that a rotating black hole in a magnetic field could provide energy. The lines of the magnetic field twist due to the frame dragging and create an effective electric charge. As the charge discharges, the rotational energy of the black hole is extracted out. If we consider a typical supermassive black hole (about a trillion Sun masses), that would give an energy of about 10^(55) Joules, which is a hundred trillion times (or 14 orders of magnitude!) more than how much energy is needed across the globe at the moment. This is however only one of the processes, the so-called magnetic, whose efficiency increases with the mass of the black hole and the intensity of the surrounding magnetic field.

"Rebellious" particles force a black hole to glow

"A black hole can only release energy through the radiation of a charged particle, from a shell we call the ergosphere. This is a zone of a black hole above the event horizon, from which particles can still escape," describes Dr. Arman Tursunov, one of the co-authors of the work. He explains that for black holes to release energy in this way, the black hole must rotate. "We don't see black holes directly, but we assume they rotate, because that's the nature of every object in the universe. Around the rotating black holes, simply speaking, "rebellious" charged particles - those that do not move in the direction of the black hole's rotation - become energy carriers, accelerate, and escape. As a result of the law of conservation of energy, the black hole itself "suffers" and this results in a slight slowdown in its rotation." Such particles enter the vicinity of black holes from crumbling objects - the more material is in the vicinity of a material black hole, the greater the source of radiation energy the black hole becomes.

Supermassive black holes can produce very strong and life-threatening radiation that can destroy civilizations across the galaxy. artistic illustration: ESO. Supermassive black holes can produce very strong and life-threatening radiation that can destroy civilizations across the galaxy. artistic illustration: ESO.

Charged black hole is enough

A black hole does not necessarily have to rotate to be a source of energy. it only must have an electric charge. The so-called the electric Penrose process shows us that charged particles, which fall into a black hole, charge the black hole itself. The size of the total charge can't grow indefinitely, eventually it will happen that another spray of particles with the same charge will be repelled by a black hole. Because giant forces act around the black hole, the charge of unabsorbed particles is ejected - the closer the cloud of particles to the black hole is and the larger the black hole's charge in comparison to its size is the stronger acceleration will particles gain. "The efficiency of such radiation is about 100,000 times less than the magnetic Penrose process, but that could still give an energy up to a trillion times greater than our civilization needs at the moment," adds Dr. Martin Kološ, co-author of scientific work.

Danger to the whole galaxy

Penrose processes have the highest efficiency in supermassive black holes in the galactic nuclei of large galaxies. From Earth, we also observe so-called active galaxies, ie those in whose nuclei black holes are extremely radiation active. Such galaxies are a completely inhospitable place to live due to the extremely strong radiation fluxes from their central black hole. During rapid events - when such a black hole absorbs a massive cloud of stellar matter - large fluxes of protons, ions and free electrons are released, which are about 100 trillion times stronger than we know from solar flares. An Earth-like planet would therefore not save life on its surface with its magnetic shield, even if it orbits a star at the very edge of the galaxy. Even more far-reaching effects has the radiation released by the black hole poles, in so-called jets. Such energy accelerated by the mentioned phenomena can have devastating consequences even at greater distances.

We are alert in our Galaxy, the solution is concrete shielding

If our black hole would be about to emit dangerous radiation, we would get to know it in advance from the radiation in the ergosphere. "If we would see an increase in energy in the ergosphere, it would mean that the Penros radiation process has intensified. It amplifies other energy processes and is in fact an indicator of the future large energy release. People on Earth would thus have to hide in underground concrete bunkers from potentially lethal radiation and stay there for several days to weeks until the level of radiation on the surface would return to normal.” Summarizes the study's results Dr. Kološ.
"The black hole in the center of our Galaxy is relatively calm," reassures prof. Zdeněk Stuchlík, director of the Institute of Physics in Opava and co-author of scientific work. "But we should still be vigilant. If, for example, a central black hole devoured an object with a strong magnetic field, the so-called magnetar - of which there are several around it - this collision would cause the rapid acceleration of charged particles into all directions, including Earth. So, it would be good to monitor the galaxy center processes. However, we do not expect to be hit by the radiation of the jets. According to available observations, the rotational poles of our central black hole are not heading in our direction."