A Black Hole is the region of Universe(space-time) from which nothing can escape not even light due to strong Gravity.Black holes are “black” because nothing, not even light,can escape their gravitational pull.
Black holes of stellar mass are expected to form when very massive stars collapse at the end of their life cycle. After a black hole has formed it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes,supermassive black holes of millions of solar masses may form. There is general consensus that supermassive black holes exist in the centers of most galaxies. Matter falling onto a black hole can form an Accretion Disc heated by friction, forming some of the brightest objects in the universe.An accretion disc is a structure formed by diffuse material in orbital motion around a central body.The central body is typically a star.Gravity causes material in the disc to spiral inward towards the central body.Gravitational forces compress the material causing the emission of electromagnetic radiations.The core of our milky way galaxy contains a supermassive black hole of about 4.3 million solar masses.Schwarzschild Radius is the distance around black hole which is completely dark and once inserted nothing can return back,it is point of no return also called Event Horizon.Nothing, not even light, can escape from inside the event horizon. The event horizon is referred to as such because if an event occurs within the boundary, information from that event cannot reach an outside observer, making it impossible to determine if such an event occurred.
When a large star runs out of fuel it can no longer support its heavy weight and the iron core of a massive star starts collapsing, it might stop when the entire core of the star has the density of an atomic nucleus, making it a neutron star. If the core is massive enough—more than 3 solar masses—the collapse becomes unstoppable, and the result is a black hole. In the case of ordinary stars, equilibrium is reached when the outward-directed forces of radiation pressure, derived from fusion reactions, are in balance with the inward directed forces of gravity. But if the force of gravity is large enough, the collapse is apparently unstoppable, and not even neutron degeneracy can save the star’s corpse. Remember a white dwarf evolves from a low-mass parent star (a star less than 5 to 10 solar masses) and the resulting white dwarf can be no more massive than 1.4 solar masses. If it has a higher mass, gravity will overwhelm the tightly packed degenerate electron pressure, and the core will continue to collapse. When a star’s mass is greater than 1.4 solar masses, its core collapse continues, and it will blow off its outer layers as a supernova. If the mass of the remaining core is greater than 1.4 but less than 3 solar masses, the remnant will be a neutron star. Astronomers believe a neutron star can be no more massive than about three times the mass of the Sun.Beyond this point, its core of neutrons will yield to gravity’s pull. When an extremely massive star is ripped apart in a supernova explosion, it can produce a supernova remnant so massive that the subsequent core collapse cannot be stopped. When this happens, nothing escapes the attractive forces near the core—not even electromagnetic radiation, including visible light photons. This is a black hole, so called because not even light can get out. But how do we talk about the size of a black hole when we have just described it collapsing without end? Is it infinitely small?
Well, in fact, it does collapse to a point called a “singularity”; But how can we talk about the “surface” of a black hole? A black hole has collapsed to a point of infinite density, and a point, by definition, has no surface.
How “big” would an Earthmass black hole be? If the Earth were compressed to the size of a marble—yet retained its current mass a velocity greater than the speed of light would be required to escape its marblesized surface. Such an object would be, effectively, a black hole. Black holes are “black” because nothing, not even light,can escape their gravitational pull.
A neutron star is one possible remnant of a massive star that has exploded as a supernova.Black holes are the other possible remnant of collapsed massive star cores; if the core has a mass greater than three solar masses, the collapse cannot stop and a black hole is born.