The document discusses black holes and their properties. It describes how John Archibald Wheeler coined the term "black hole" and how Pierre Simon Laplace first proposed the concept in 1795, calculating that an object compressed into a small enough radius would have an escape velocity greater than the speed of light. It provides details on escape velocity and the event horizon of a black hole, beyond which nothing, not even light, can escape. The document classifies different types of black holes by mass and size.

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