What are Black Holes?

 

Black Hole is a certain region which has an extremely high gravitational field. It is a large amount of matter concentrated into a very small area. These can be very large or very tiny. While smallest Black Hole is like an atom, a large one could be even million times bigger than sun. Largest of these are called supermassive. Scientists assume that every galaxy has a supermassive Black Hole at its centre. The Black Hole which is at the centre of our galaxy- Milky Way- is called Sagittarius-A.

Formation of a Black Hole

 

When there is a massive star which has a mass equal to millions of times like sun its gravitational field become unstable. Gravitational field intensity is counted by g=GM/R^2 equation.

g=gravitational field intensity. G=Universal gravitational constant M= mass of the star or planet R= radius. According to the equation if a star has a great mass equals million times of earth’s mass, but the same radius, its gravitational field intensity will be million times greater than earth’s. According to F=mg equation for a given mass, the gravitational force (F) on the surface of that star is million times greater. Because of this intolerable gravitational force star begins to fall in upon itself. When an unstable star collapses it begins to explode. This is called super-nova. It releases a great amount of energy to the universe during the explosion. And also during the super-nova, star’s mass begins to concentrate around its centre. Sometimes it becomes as tiny as an atom. On this stage it is called a Black Hole. Because of its high intensity of the gravitational field every object goes near by it falls into it. But fortunately solar system is not close enough to any Black Hole for earth to fall into a black hole.

Why are Black Holes ‘‘Black’’?

 

In order to escape from a certain planet and reach the space, every object needs a certain velocity which depends on the Mass and the Radius of the planet. This minimum velocity is called escape velocity (V). It is counted by v=√(2GM/R) equation. According to this equation due to Black Hole’s great mass (M) and tiny value of radius ( R), the minimum velocity which needs to escape to the space becomes even greater than the velocity of light which is roughly 3×10^8 meters per second. Escape velocity on the surface of the earth is around 1.1 ×10^3 meters per second. In that case even light cant escape from Black Holes and that is why those appear in black.