# Black holes

IT Analyst at Tata Consultancy Services em Tata Consultancy Services
24 de Aug de 2012
1 de 12

### Black holes

• 1. (The burial of massive stars)
• 3. 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 Newton's 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.
• 4. 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
• 5. In black holes the Escape velocity> 3,00,000 km/sec  even light cann’t escape through it.
• 6. 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.
• 7. Event horizon is a spherical surface that marks the boundary of the black hole .  You can pass in through the horizon, but you can't get back out of it.
• 9. 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 .
• 10. Class Mass Size Supermassive ~105 - 109 Msun ~0.001–10 AU Intermediate-mass ~103 MSun ~103 km = REarth Stellar-mass ~10 Msun ~30 km Primordial ~Mmoon ~0.1 mm
• 11. 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.
• 12. The