What Is a Black Hole ?

Black holes are the most fascinating and mysterious objects in our universe. When comparing the mass and space of Black hole, it is a massive collection of mass in a tiny space. Due to that black holes have massive gravitational fields even the photons (the fastest particles) can't escape this gravitational field. If there is a Black Hole, what we can observe is a massive dark area, because even light can't escape it. The only method of identifying a Black Hole is the effects of its gravitational field on surrounding objects. 

Event Horizon

The dark area around the black hole is the Event Horizon. If you throw some object to a black hole, it's getting accelerated due to its gravitational field. At a certain point, its speed will be equal to the speed of light. That point is the Event Horizon. When an object reaches the speed of light, it's flow of time will be frozen. Then all the laws of physics will be irrelevant. Therefore, we have no clear idea, of what is beyond this event horizon and the singularity is way beyond event horizon. Even today we have no accurate way to identify its composition. So what is the origin of this massive group of mass to create a black hole? All the stars in the universe are made with Hydrogen Nuclear fusion is fusing them to make Helium and radiating massive amount of energy. That radiation is pushing the Hydrogen away and gravity is pulling in. A star has a spherical shape due this this hydrostatic equilibrium If this is a massive star, Helium could be fused to bigger elements and process goes further till they create Iron (Fe) and they are getting deposited in the core.

Down the time more Hydrogen getting fused and radiation is getting reduced. But gravity remains the same. At a certain point gravity exceed the pressure of radiation and the star collapse in to itself in few seconds. 

Supernova & Neutron Star

Then star goes to a brutal Supernova explosion. This is spreading out elements that cooked in the star. That how everything around us, even humans are created. If the star is large enough, it will become a Neutron Star. If it's super massive, it will create a singularity and then a Black Hole Due to massive gravitational field, Black Hole can suck nearby objects even light. So, you must be thinking it's infinite. But even black holes have a finite life time. Throughout the universe there are virtual particles. They are in pairs with + and – mass. In a very short time they annihilate each other to pure energy. If there is a virtual particle pair near event horizon Particle with + mass might get escaped. Particle with - mass get sucked in and that will reduce the mass of singularity. Escaped particle will become radiation. This is a theory by famous “Stephan Hawking”. So, we call it Hawking Radiation. But it's taking trillions and trillions of years to evaporate a black hole. There are several sizes of black holes. Most of them are in size of small asteroid. Some of them are couple of times bigger than solar system. We call them Supermassive black holes. They live in the center of galaxies and holding it's stars together. What is beyond event horizon? What are the compositions of singularity? Those are still mysteries! If we manage to find answers to those questions, we might be able to understand weird behavior of gravity.