Black holes are perhaps the most indescribable objects in the Universe: the concentration of such a mass that it collapses, as follows from general relativity, to a singularity at the center. Atoms, nuclei and even fundamental particles are compressed into an infinitesimal point in our three-dimensional space. Everything that falls into a black hole is doomed to remain in it until the end of time, captured by its gravity, which even light cannot leave. What is the fate of dark matter when it encounters a black hole?
Will it be sucked into the singularity like normal matter and contribute to the mass of the black hole? If so, when the black hole evaporates due to Hawking radiation, what will happen to dark matter?
We should start with what black holes are.
Here on Earth, if you want to send something into space, you need to overcome the Earth's gravitational pull. For our planet, the so-called escape velocity is about 11.2 km / s, it can be developed using a sufficiently powerful rocket. If we were on the surface of the Sun, the escape velocity would be much higher, 55 times: 617.5 km / s. When our Sun dies, it will shrink to a white dwarf, which will be the size of the Earth, but will be half the mass of the current Sun. On it, the escape velocity will be about 4570 km / s, which is about 1.5% of the speed of light.
This is important because you are concentrating more and more mass in a particular region of space, and the escape velocity for that object is getting closer and closer to the speed of light. And as soon as your escape velocity on the surface of an object reaches or exceeds the speed of light, not only light will no longer be able to leave it - as far as we understand matter, energy, space and time today - this entire object will collapse into a singularity. The reason is simple: all fundamental forces, including the forces that hold atoms, protons, or even quarks together, cannot travel faster than the speed of light. Therefore, if you are at a certain point from the central singularity and are trying to keep a distant object from gravitational collapse, you cannot; collapse is inevitable. And all you need to overcome this barrier is a star 20-40 more massive than the Sun.
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When its core runs out of fuel, the center will explode under its own gravity, creating a catastrophic supernova, inflating and destroying the outer layers, but leaving a black hole in the center. Such black holes grow over time, absorbing any matter and energy that gets too close. Even moving at the speed of light, you can get into it and never leave the event horizon. Due to the curvature of the space itself inside the black hole, you will also inevitably fall into a singularity at the center. When this happens, you simply add energy to the black hole.
Outside, we cannot say what the black hole originally consisted of - protons, electrons, neutrons, dark matter, or antimatter in general. There are only three properties (so far) that we can observe about a black hole from the outside: its mass, its electric charge and its angular momentum, a measure of rotational motion. Dark matter, as far as we know, does not have an electric charge, as well as other quantum characteristics (color charge, baryon number, lepton number, etc.), which may or may not be preserved or destroyed, based on the information paradox of a black hole.
Because of how black holes form (from explosions from supermassive stars) when they first form, black holes are 100% regular (baryonic) matter and 0% dark matter. Do not forget that dark matter interacts only gravitationally, unlike ordinary matter, which interacts through gravitational forces, weak, electromagnetic and strong interactions. Yes, large galaxies and their clusters have five times more dark matter than ordinary matter, but it gathers into one large halo. In a typical galaxy, this dark matter halo extends for several million light years, spherically, in all directions, while ordinary matter is concentrated in a disk that occupies 0.01% of the volume of dark matter.
Black holes tend to form inside the galaxy, where ordinary matter completely predominates over dark matter. Imagine the region of space we are in: around our sun. If we draw a sphere of 100 AU. e. (a.u. is the distance from the Earth to the Sun) around our solar system, we will enclose all the planets, moons, asteroids and the entire Kuiper belt, but the baryonic mass - ordinary matter - enclosed in our sphere, will be mostly represented Sunshine and weigh about 2 x 1030 kg. On the other hand, the total amount of dark matter in the same sphere will be only 1 x 1019 kg, or 0.0000000005% of the mass of ordinary matter in the same region, equal to the mass of a modest asteroid the size of Juno, about 200 kilometers across.
Over time, dark matter and ordinary matter will collide with this black hole, be absorbed and add to its mass. Most of the mass growth will come from ordinary matter, not dark matter, but at some point, many quadrillion years into the future, the black hole's decay rate will finally exceed the black hole's growth rate. Hawking's radiation process will cause particles and photons to exit the black hole's event horizon, conserving all the energy, charge, and angular momentum of the black hole's interior. This process will take from 1067 years (for a black hole with solar mass) to 10100 years (for the most massive black holes).
This means that some dark matter will come out of black holes, but will be completely different from the volume of dark matter that entered the black hole initially. All black holes have a memory of the things that got into it, in the form of a small set of quantum numbers, and this amount of dark matter is not included in them (remember, it does not have all the quantum characteristics?). The output will be completely different from the input.
Thus, dark matter is another food source for black holes, and far from the best. Moreover, it is a completely uninteresting food source. It has little or no effect on black holes.
ILYA KHEL