1. (The burial of massive stars)

2. The name black hole was invented by JohnArchibald Wheeler . Before Wheeler came along, these objects wereoften referred to as frozen stars. The concept of black hole was first proposed byPierre Simon Laplace in 1795. Using Newtons Theory of Gravitation ,Laplacecalculated that if an object were compressed intoa small enough radius, then the escape velocityof that object would be faster than the speed oflight. 3. The velocity at which the body is thrown insuch a way that it does not return again. This is the concept used for rocketpropulsion. on earth it is 11.2 km/sec on moon it is 2.4 km/sec 4. In black holes theEscape velocity> 3,00,000 km/sec even light cannt escape through it. 5. Stars rotate around the centers of galaxy withtheir own gravitational energy. When their energy comes to an end , theycollapse in their own gravity . This forms a black hole. 6. Event horizon is a spherical surface thatmarks the boundary of the black hole .You can pass in through the horizon, but youcant get back out of it. 7. A typical mass for a black hole would beabout 10 times the mass of the Sun, or about10^{31} kilograms.(10,000,000,000,000,000,000,000,000,000,000 kgs) Astronomers also suspect that the weight canbe upto 10^{36} kgs.(a million times a sun)A black hole with a mass equal to that of theSun would have a radius of 3 kilometers. So a typical 10-solar-mass black hole wouldhave a radius of 30 kilometers . 8. ClassMass Size Supermassive ~105 - 109 Msun~0.00110 AUIntermediate-mass ~103 MSun ~103 km = REarthStellar-mass~10 Msun~30 kmPrimordial~Mmoon~0.1 mm 9. Astronomers are confident that our own MilkyWay galaxy has a supermassive black hole at itscenter, in a region called Sagittarius A. A star called S2 (star) follows an elliptical orbit witha period of 15.2 years and a pericenter (closest)distance of 17 light hours from the central object. 10. The