[Creative Cultivation Program] Is it possible to get energy from a black hole?

Author: Gou Lijun

This time we are going to talk about the energy of black holes. In fact, it is possible to get energy from black holes. But to understand the energy of black holes, we must first start with the formation of black holes. In the universe, there are stars of different masses, some are about the same mass as our sun, some are less than our sun, some are more than our sun, and some are much more than our sun. According to the existing theory of stellar evolution, when a celestial body similar to our sun or less than about 8 times the mass of the sun dies, the central part of the star will become a white dwarf. And those celestial bodies between 8 times the mass of the sun and 20 times the mass of the sun will become a neutron star when they finally die. And those celestial bodies with an initial mass of about 20 times the mass of the sun will eventually collapse into a black hole. The reason why black holes are formed is that there is no known force to support other celestial bodies.

Black holes can usually be divided into Schwarzschild black holes and Kerr black holes. A Schwarzschild black hole is a black hole that does not rotate, while a Kerr black hole is a black hole that rotates. Of course, we usually imagine that the energy that makes the black hole rotate can be extracted in some way. If this is the case, we can imagine that for a Schwarzschild black hole, that is, a black hole that does not rotate, there should be no energy that can be extracted. However, this is not the case. According to current statements, for a black hole that does not rotate, there should be about 6% or more of the energy that can be extracted, which is actually a bit different from our usual understanding. For a rotating black hole, we know that the rotation speed of the black hole's event horizon can be close to the speed of light, so at this time the energy that can be extracted from the black hole is close to 42%, which is already very high. The mass of the black hole that we see actually includes the rotational energy of the black hole.

In astrophysics, there is usually an accretion disk around a black hole. Part of the matter in the accretion disk will slowly fall into the black hole, and the other part of the matter will be ejected along the axis of rotation of the black hole. In astronomy, we call the matter along the axis of rotation ejected matter or jet. What is the energy mechanism of this part of matter? In fact, it is the rotational energy of the black hole, which is the energy we mentioned above. So can we extract this energy artificially? Some people have come up with a method similar to the Dyson sphere, which is placed around a normal star to extract the energy radiated by the star. This is the usual Dyson sphere we know. Based on this idea, some people thought of placing a similar Dyson sphere around a black hole. Of course, this device is more complicated, and then the rotational energy of the black hole is gathered and utilized. Kip Thorne, who once won the Nobel Prize, once mentioned how to extract the energy of black holes in his popular science book "Black Holes and Time Warps". In addition, there are some theoretical studies on the possibility of the existence of planets around black holes. The final result is that planets can also exist around black holes because the gas disk around the black hole can provide certain radiation.

So can we really use the energy of black holes? In the early 1960s, the former Soviet cosmologist Kardashev hypothesized a three-level model of cosmic civilization based on the level and total amount of energy that civilization can master and use. The first-level cosmic civilization can be called a planetary civilization, which means that it can use all the energy and resources on the planet. The second-level cosmic civilization is a stellar civilization, which means that it can use all the resources of the entire star system. The third-level civilization is a galaxy civilization, which means that it can use the resources of the entire galaxy. According to the current capabilities of human beings, we are still in the first-level civilization, with a level of 0.7. As for the black hole we mentioned, it still belongs to the level of a star and should be in the next civilization. We are still far from it.

Although we have not yet reached the point of utilizing the energy of black holes, we need to consider first whether we live around this black hole. In the Milky Way, it is estimated that there are hundreds of millions of stellar-mass black holes, but so far, we have discovered less than 100 stellar-mass black holes. Among the less than 100 black holes discovered, less than 20 to 30 have been accurately measured, so it can be said to be the tip of the iceberg. According to our current understanding, some black holes rotate slowly, and some rotate quickly, so the energy that can be extracted from different black holes should be different. According to our current understanding, the stellar-mass black hole closest to the Earth or the Sun is A0620, which is a black hole named after the satellite that discovered it. It is about 3,000 light-years away from us, so this black hole is very far away. For us to want to utilize its energy, it should be unlikely for us at present.

So the simple answer to this question again is: whether it is a rotating black hole or a non-rotating black hole, in theory we can extract energy from the black hole, but because

The distance is too far, and the level we are currently at is too low, so we have no way to operate it. I hope that humans in the future can do it.

This article is produced by the Science Popularization China-Creation Cultivation Program. Please indicate the source when reprinting