10 facts about black holes, which everyone should know
Black holes - this is perhaps the most mysterious objects in the Universe. Unless, of course, somewhere in the depths of not hiding things, the existence of which we do not know and can not know that it was unlikely. Black holes - this is an enormous mass and density, compressed at one point a small radius. The physical properties of these objects are so strange that they make to puzzle most experienced physicists and astrophysicists. Sabina Hossfender, a theoretical physicist, made a compilation of ten facts about black holes, which everyone should know.
What is a black hole?
The defining feature of a black hole is its horizon. This border, breaking which nothing, not even light, can not go back. If the area becomes separated separated forever, we are talking about the "event horizon". If it is only temporarily separated, we talk about "the visible horizon." But it is "temporarily" can also mean that the region will be separated for much longer the current age of the universe. If the horizon of a black hole is a temporary but long-lived, the difference between first and second spreads.
How big black hole?
It is possible to imagine the horizon of a black hole as a sphere, and its diameter is directly proportional to the mass of the black hole. Therefore, the greater the mass falls into the black hole, the more it becomes a black hole. Compared with stellar objects, however, are tiny black holes, because the mass is compressed into very small volumes under the irresistible gravitational pressure. The radius of the black hole mass to the planet Earth, for example, only a few millimeters. This is 10 billion times smaller than the radius of the Earth. The radius of the black hole is called the Schwarzschild radius after Karl Schwarzschild, who first brought the black hole as a solution to Einstein's general theory of relativity.
What's happening on the horizon?
When you cross the horizon, much is happening around you nothing. All because of Einstein's equivalence principle, which implies that you can not tell the difference between the acceleration in flat space and gravitational field, creating the curvature of space. Nevertheless, the observer away from the black hole, which is watching as someone else falls into it, notice that people will move more and more slowly, approaching the horizon. If time near the event horizon is moving slower than the distance from the horizon. However, it will take some time, and falling into the hole observer cross the event horizon and is inside the Schwarzschild radius.
What you are experiencing on the horizon depends on the tidal forces of the gravitational field. Tidal forces on the horizon are inversely proportional to the square of the mass of the black hole. This means that the more and more massive the black hole, the less force. And if a black hole is massive enough, you can overcome the horizon before I noticed that something was going on. The effect of the tidal forces will stretch you, a technical term that is used for this purpose of physics, called "spaghettification".
In the early days of the general theory of relativity it was believed that on the horizon there is a singularity, but it was not so.
What's inside a black hole?
No one knows for sure, but not exactly a bookshelf. General relativity predicts that a black hole singularity, a place where the tidal forces become infinitely large, and once you get over the event horizon, you can not get anywhere else, except in the singularity. Accordingly, it is better not to use general relativity in these places - it simply does not work. To say what happens inside a black hole, we need a theory of quantum gravity. It is recognized that this theory replaces the singularity of something else. How do black holes form?
At present, we know of four different ways of formation of black holes. It is best to understand associated with stellar collapse. A big enough star forms a black hole after its fusion ceases, because all that was possible to synthesize, was synthesized. When the pressure generated by the synthesis stops, the substance starts to fall to its own gravitational center, becoming more dense. In the end, it is sealed so that nothing can overcome the gravitational effect on the star's surface, Thus is born a black hole. These black holes are called "black holes of solar mass" and are the most common.
The next common type of black holes are "supermassive black hole" that can be found in the centers of many galaxies and have a mass of about a billion times greater than the solar mass black holes. While not known exactly how they are formed. It is believed that once they started out as a black hole of solar mass, which in densely populated galactic centers absorbed a host of other stars and grow. Nevertheless, they seem to absorb substances faster than expected this simple idea, and how they do it - is still the subject of research.
More controversial idea became primordial black holes, which can be formed into virtually any weighing of large density fluctuations in the early universe. Although it is possible, quite difficult to find a model that produces them, without creating an excessive number of them.
Finally, there is a very speculative idea that the Large Hadron Collider can form tiny black holes with masses close to the mass of the Higgs boson. This works only if our universe has extra dimensions. While there was no evidence to support this theory.
How do we know that black holes exist?
We have a lot of observational evidence for the existence of compact objects with large masses, which do not emit light. These objects posing by gravitational attraction, e.g., due to movement of other stars or gas clouds around them. They also create gravitational lensing. We know that these objects do not have a solid surface. This follows from the observation because the material falling on the object with the surface should cause release of more particles than the material falling through the horizon.
Why last year, Hawking said that black holes do not exist?
He meant that black holes are not eternal horizon of events, but only a temporary apparent horizon (see. The first paragraph). In a strict sense, only the event horizon of a black hole is considered.
How do black holes emit radiation?
Black holes emit radiation due to quantum effects. It is important to note that this is the quantum effects of matter, rather than the quantum effects of gravity. Dynamic space-time of a collapsing black hole modifies the definition of the particle itself. Like the current time, which is distorted near the black hole, the concept of the particles is too dependent on the observer. In particular, when an observer falling into a black hole, I think that falls in a vacuum, the observer away from the black hole, thinks this is not a vacuum, and the total area of the particles. It is stretching space-time causes this effect. First discovered by Stephen Hawking radiation emitted by a black hole is called "Hawking radiation." This radiation has a temperature is inversely proportional to the weight of the black hole is less than a black hole, the higher the temperature. In stellar and supermassive black holes that we know, the temperature significantly below the temperature of the microwave background and therefore not observed.
What information paradox?
information loss paradox is due to Hawking radiation. This radiation is purely thermal, ie coincidence of certain properties is only the temperature. The radiation itself does not contain any information about how to form a black hole. But when the black hole emits radiation, it loses mass and shrinking. All of this does not depend on the material, which became part of the black hole, or from which it was formed. It turns out that knowing only the final state of the evaporation can not be said of what a black hole is formed. This process is "irreversible" - and the catch is that in quantum mechanics there is no such process.
It turns out that the evaporation of a black hole is incompatible with quantum theory, as we know it, and with this need to do something about it. Somehow eliminate inconsistency. Most physicists believe that the solution lies in the fact that Hawking radiation must somehow contain information.
What Hawking offers solutions for information paradox of the black hole?
The idea is that the black hole must be a way to store information that has not yet been adopted. Information is stored on the horizon and the black hole may cause displacement tiny particles in the radiation Hawking. In these tiny displacements may be trapped inside information about the matter. The exact details of this process are not currently defined. Scientists await more detailed technical paper by Stephen Hawking, Malcolm Perry and Andrew Strominger. They say he will be in late September. At the moment, we believe that black holes exist, and we know where they are, both are formed and what will be the result. But the details of what happens to incoming information they still represent one of the biggest mysteries of the universe.