Black Hole. Area of space-time that nothing can leave.
The Black Hole is a creation of gravity, which is subject to both small particles and large masses, and even light.
The term "Black Hole" was created very recently, introduced in 1969 by an American scholar John Wheeler, presenting with his help a pictorial idea that appeared for the first time at least 200 years ago. They existed then two competing theories of light: according to the first, supported by Newton, the light consisted of particles, the second the theory, however, was that light is waves. Today we know that basically both theories are correct.
After stating that the speed of light is finite, one should assume that gravity can have a significant effect on the movement of light.
This assumption was used by John Michell, a professor at Cambridge, in his work from 1783, published in Philosophical Transactions of the Royal Society of London. The Michell showed that a star with sufficiently large mass and density would produce such a strong gravitational field that the light could not leave it. Any light radiated from the surface of the star it would have been attracted back by gravity before it could move away. Michell suggested that such stars could be very much. Although we would not see their light, we would be able to detect their presence by attracting them gravity. Today, these objects are called Black Holes, because that's how they look: black, not glowing areas in space.
Stars are incredibly massive collections of mostly hydrogen atoms that collapsed from enormous gas cloud under their own gravity. In their core, nuclear fusion crashes hydrogen atoms into helium releasing enourmous amount of energy. This energy, in form of radiation pushes against gravity maitaing balance between two forces.
The core of the star is iron, which doesn't generate energy and builds up in the center of the star until it reaches it's critical amount. This phenomenon disturbs balance between gravity and radiation, which leads to collapse of the star's core and star implodion. Next moving at about quarter of the speed of light, feeding more mass into core, the star dies, in a supernova explosion. This produce either a Neutron Star, or if the star is massive enough the entire core collapses into a Black Hole.
Anything that crosses the event horizon of Black Hole needs to be travelling faster than the speed of light to escape, in other words it's impossible. So what we really see is just a black sphere reflecting nothing. It is possible to connect Black Holes consisting in the front collision of two Black Holes and join one. The surface of the horizon of the resulting Black Hole is then larger than the total surface of the horizons of the colliding holes.
The experience of time is different around black holes, from the outside objects seems to slow as they approach the event horizon, so time passes slower for them. At some point this would make them freeze in time and disappear. While from the other perspective the rest of universe could be seen fast forward, kind of like seeing into the future. Right now we as a humanity don't now what happens next, but every body known to us will be destroyed and torn apart, the only hypothetical elementary particle that would move at a speed faster than the speed of light in a vacuum is called Tachion. However, there is no evidence for the existence of these particles.
The huge massive Black Holes are placed in a hearth of every galaxy, and are feeding for billion of years. Currently, the largest super massive Black Hole known, is "S5 0014+81". It's size is about 40 billion times as the mass of Sun.
The process called "Hawking radiation" can make Black Hole eventually to evaporate. Black hole emitting radiation loses mass. If this loss is not balanced by the mass falling into it, then the radiation becomes stronger, which can even cause the Black Hole to evaporate completely. To explain the matter in a clearer way, we can say that at the edge of Black Hole there is a phenomenon in which virtual particles popping into existence and annihilating each other again. It leads to that one of the virtual particles will be drawn into the Black Hole, and the other will escape and become real particle. So Black Hole will be losing it's energy, but this process happens incredibly slow.
It is believed that when the black hole decreases to the expected surface, it will radiates away with energy of billions nuclear bombs in huge explosion.
In April 2017, scientists began collecting data on _Sagittarius A_*, a supermassive Black Hole located in the center of the Milky Way. All data has already been downloaded by scientists and their in-depth analysis begins, which means that soon we can see the first photo of a black hole in history.
References:
[1]http://www.kchn.pg.gda.pl/didactics/nukleogeneza_krotka_historia_czasu.pdf
[2]http://www.fuw.edu.pl/~kostecki/czarne_dziury.pdf
[3]http://www.astronomia.biz.pl/czarnedziury.html
[4]http://www.astro.sunysb.edu/rosalba/astro2030/BlackHoles.pdf
[5]https://www.physicsoftheuniverse.com/topics_blackholes_theory.html
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