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# Black holes

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### Black holes

1. 1. (The burial of massive stars)
2. 2.  The name black hole was invented by John Archibald Wheeler . Before Wheeler came along, these objects were often referred to as frozen stars. The concept of black hole was first proposed by Pierre Simon Laplace in 1795. Using Newtons Theory of Gravitation ,Laplace calculated that if an object were compressed into a small enough radius, then the escape velocity of that object would be faster than the speed of light.
3. 3.  The velocity at which the body is thrown in such a way that it does not return again. This is the concept used for rocket propulsion. on earth it is 11.2 km/sec on moon it is 2.4 km/sec
4. 4. In black holes theEscape velocity> 3,00,000 km/sec even light cann’t escape through it.
5. 5.  Stars rotate around the centers of galaxy with their own gravitational energy. When their energy comes to an end , they collapse in their own gravity . This forms a black hole.
6. 6.  Event horizon is a spherical surface that marks the boundary of the black hole . You can pass in through the horizon, but you cant get back out of it.
7. 7.  A typical mass for a black hole would be about 10 times the mass of the Sun, or about 10^{31} kilograms. (10,000,000,000,000,000,000,000,000,000, 000 kgs) Astronomers also suspect that the weight can be upto 10^{36} kgs.(a million times a sun) A black hole with a mass equal to that of the Sun would have a radius of 3 kilometers. So a typical 10-solar-mass black hole would have a radius of 30 kilometers .
8. 8. Class Mass Size Supermassive ~105 - 109 Msun ~0.001–10 AUIntermediate-mass ~103 MSun ~103 km = REarthStellar-mass ~10 Msun ~30 kmPrimordial ~Mmoon ~0.1 mm
9. 9.  Astronomers are confident that our own Milky Way galaxy has a supermassive black hole at its center, in a region called Sagittarius A. A star called S2 (star) follows an elliptical orbit with a period of 15.2 years and a pericenter (closest) distance of 17 light hours from the central object.
10. 10. The