Black holes are extremely dense objects having size relatively smaller than their mass. Due to high gravity near a black hole not even light can escape. The light is attracted towards black hole because according to Einstein’s special theory of relativity E=mc^2 `i.e. energy is equivalent to mass.

How are they formed?

  • Black Holes are formed due to explosion of massive stars and such explosion is called supernova.

  • Due to nuclear fusion formation of iron takes place which stop producing further energy and hence outward pressure reduces and star implodes.

  • In particle accelerators a lot of energy is produced in a very small region which leads to accumulation of lot of mass in that small region. This leads to formation of micro-black holes. They aren’t dangerous as they evaporate very easily.

Detection of Black Hole

  • Detection of black holes can be done by observing its surroundings like if some celestial bodies revolve around something invisible it gave the idea of presence of a black hole around which they must be revolving.

  • Event horizon is the brightest region around the black hole. By observing or understanding event horizon the real condition inside the black hole can be predicted.

Schwarzchild Radius (Rs)

The Schwarzchild Radius (Rs) is the radius of the event horizon within which nothing can escape the black hole, including light. It was determined by Karl Schwarzchild using Einstein’s general theory of relativity and completely depends on the mass (M) of the block. The formula is

Rs = 2GM/c^2
where G is the universal gravitational constant and c is speed of light.

Why is it Black?

A black hole is so called black because it cannot be seen. According to the general theory of relativity there is no gravitational force existing. The mass of body bends space-time geometry in such a way that anything surrounding it moves towards its centre. Similarly, a black hole forms that much strong curvature that it forms a hole. Hence black hole is called ‘hole’.

Time Dilation

According to ‘Time Dilation’ effect explained in general theory of relativity flow of time slows down in the region of strong gravity. So near a black hole time would also slow down.

Lord Kelvin’s theory of Milky way

Lord Kelvin wanted to find the total weight of Milky Way of earth. So he found it in two ways. The first one was done by calculating total no. of stars and multiplying it by the density of a single star. The other one was done with the help of gravitational formula. The difference between the two calculation leads to the thought of presence of dark matter in the universe.

  • Matter which is not visible through naked eyes but exert gravitational force is called dark matter.

  • Scientists found other galaxies moving away from us at accelerating speed which leads to the presence of dark energy in the universe.

The energy which makes everything away from each other is called dark energy.