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