ब्लॅक होल के बारे मे सबकुछ || Everything About Black Holes
Channel: UpStep
Date: 18/09/2019

Its all about escape velocity. For throwing an object outside Earth’s gravitational field we require minimum velocity. This velocity is called as escape velocity.

The escape velocity for Earth is 11.2 km/s. Neglecting air atmosphere on earth if we throw any object with 11.2 km/s then that object escapes Earth’s gravitational field and travels in space. If we do same thing on moon, ball must be thrown by 2.4 km/s velocity to make escape from moon’s gravitational field. It means escape velocity of moon is 2.4 km/s. For Sun, the escape velocity is 618 km/s. 
The escape velocity of white dwarf having mass equal to sun is 6451 km/s, the escape velocity of neutron star is 150000 km/s which is half the speed of light. The escape velocity of black hole is greater than 300000 km/s that is greater than speed of light. It means light also cannot escape black hole. This is what the black hole. This is the object from which light doesn’t escape that’s why we cannot see that object hence named black hole. The value of radius of the object at which its escape velocity becomes equal to speed of light is called Schwarzschild radius. The Schwarzschild radius of Sun is 3 km, it means Sun will become black hole if it compressed to sphere of 3 km radius. Schwarzschild radius of Earth is 9 mm, not even 1 cm. if the Earth having radius 6400 km compressed to small marble size, Earth will become black hole.