When black holes become unstable?
There are several ways to create a black hole from collapsing supernova core to the merger of neutron stars with the collapse of a huge number of substances. If we take the lower limit, black holes may be 2, 5 - 3 solar mass, but the upper limit supermassive black holes may exceed the weight at 10 billion solar. They are usually found in the centers of galaxies. As far as they are stable? What is a black hole dries up first: a large and voracious or small?
Is there a critical size for the stability of a black hole? A black hole weighing 10 12 kilograms can be stable for several billion years. But the black hole in the weight range of 10 5 may explode in a second, and definitely will not be stable. Where is the middle ground, where the influx of matter is equal to Hawking radiation?
The stability of black holes
The first thing you need to start, is the stability of the black hole itself. In any other object in the universe, astrophysics or another, there are the forces that hold it together against the universe, which is trying to tear it up. It represents a hydrogen atom strong structure; a single ultraviolet photon can destroy it, the ionized electrons. For the destruction of the atomic nucleus need more high-energy particles such as cosmic ray, the accelerated protons or gamma ray photon.
But larger structures such as planets, stars or even galaxies, gravitational forces that hold them, are huge. Typically, such a gap need megastructure or thermonuclear reaction, or an incredibly powerful effect of gravity from the outside - for example, from a passing star, black hole or the galaxy.
In the case of black holes, however, it is not so. Mass black hole instead distributed by volume, is compressed into a singularity. In a non-rotating black hole is a single point of zero dimension. In a rotating black hole is not much better: an infinitely thin, one-dimensional ring. In addition, the entire contents of the mass-energy of a black hole is within the event horizon. Black holes - these are the only objects in the universe that have an event horizon: the border, breaking that, you can not return. No acceleration, and therefore no force can pull matter, mass, or energy from the event horizon beyond.
This may mean that the black holes formed in any way possible, can only grow and never be destroyed. And they are growing steadily and continuously. We are seeing all sorts of phenomena in the universe, such as:
- active galactic nuclei;
- stars, emit no light;
- X-ray and radio bursts from the galactic center;
which lead us to the black holes. Determining their weight, we try to learn and the physical size of the event horizon. Anything that interferes with it, crosses or touches, inevitably fall into. And then, thanks to the conservation of energy, and to increase the mass of the black hole.
This process occurs with every black hole, known to us. Material from other stars, cosmic dust, interstellar matter, gas clouds and even light neutrinos left over from the Big Bang - everyone goes there. Any matter colliding with a black hole, increasing its mass. black hole growth is dependent on the density of matter and energy surrounding the black hole; Monster in the center of our Milky Way is growing at a rate of 1 solar mass in 3,000 years; a black hole in the center of the Sombrero galaxy is growing at a rate of 1 solar mass in 20 years.
The bigger and heavier than your black hole in the middle, the faster it grows, depending on encountering a material. Over time, its growth rate is slowing down, but because the universe only about 13, 8 billion years, black holes grow well. On the other hand, black holes are not easy to grow over time; There is also a process of evaporation: Hawking radiation. This is due to the fact that space is strongly curved near the event horizon, but straightens out when removed. If you are at a great distance, you can see a small light emitted from the curved area near the event horizon, coupled with the fact that the quantum vacuum has different properties in different areas of curved space.
The net result is that black holes emit thermal radiation of a black body (mainly in the form of photons) in all directions around itself, in a volume of space, which generally comprises about ten Schwarzschild radii at the location of the black hole. And it may seem strange, but the smaller the black hole, the faster it evaporates.
Hawking radiation - an incredibly slow process, in which a black hole with the mass of our sun evaporates through 10 64 s; hole at the center of our Milky Way - 10 87 years, and the most massive in the universe - 10 100 years. To calculate the evaporation of a black hole by a simple formula, you need to take a time-frame of our Sun, and is multiplied by (the black hole mass / mass of the Sun) 3.
From which it follows that a black hole with the mass of the Earth will live 10 47 s; a black hole with the mass of the Great Pyramid of Giza (6 million tons) - about a thousand years; with the mass of the Empire State Building - about a month; with the mass of the ordinary man - a picosecond. The less weight, the faster the black hole evaporates.
As far as we know, the universe could contain black holes unimaginably different sizes. If it was filled with light black holes - a billion tonnes - they would have evaporated by now There is no evidence that there are black holes with masses between the light and those that are born in the process of merging neutron stars - in theory, they have a weight of 2, 5 sun. Above these limits, X-ray studies indicate the existence of black holes in the range of 10-20 solar masses; LIGO showed black hole 8 to 62 solar masses; also found supermassive black holes throughout the universe. Today, all of the existing black holes are gaining matter faster than lose due to Hawking radiation. Solar mass black hole loses about 10 -28 joules of energy per second. But when you consider that:
- , even in one of the CMB photon is a million times more energy;
- 411 of photons per cubic centimeter of space left after the Big Bang;
- They travel at the speed of light, facing 10 trillion times per second per cubic centimeter;
Even an isolated black hole in the depths of intergalactic space will wait until the universe does not grow up to 10 20 years - a billion times larger than its current age - before the black hole growth rate falls below the rate of Hawking radiation.
But let's play a game. Suppose you live in intergalactic space, away from the ordinary matter and dark matter, away from all the cosmic rays, neutrinos and stellar radiation, and you still have only photons from the Big Bang, with whom you can chat. How big should your black hole to the rate of evaporation (Hawking radiation) and absorption of photons of your black hole (growth) cancel each other out?
The answer is in the region of 10 23 kg, ie approximately the mass of the planet Mercury. If Mercury was a black hole, it would have been half a millimeter in diameter and radiated to about 100 trillion times faster than a black hole of solar mass. It is with such a mass in our universe is a black hole would be absorbed as much microwave radiation as lost in the process of Hawking radiation.
But if you need a realistic black hole, you can not isolate it from the rest of the matter in the universe. Black holes, even being thrown out of the galaxies are still flying through the intergalactic medium, when confronted with cosmic rays, the light of the stars, neutrinos, dark matter and all kinds of particles, massive and massless. The cosmic microwave background is unavoidable, no matter where you go. Black holes are constantly absorb matter and energy and grow in weight and size. Yes, they also radiate energy, but to exist in our universe black holes began to run out faster than they grow, should pass about 100 quintillion years. And on the final evaporation will take even more.
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