Can someone help me with number 3?

Black Hole

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It is the most mysterious thing in our universe.

✳ John Michell was the first scientist who gave his idea on black hole in 1783

✳ later than Pière simon described black holes in his book the system of the world in 1796.

What are black holes?

=>  It is also a celestial body which have infinite gravitational force and infinite mass and even light can not escape from it.

=> If any object goes near a black hole then time slows down for that object.

How black holes formed?

=> Mostly  black holes formed because of compression of mass and density of stars.

So,  first we know how stars formed and then black holes.

= stars are formed by the cloud of  gas and dust present in our universe which we simply called as Nebula.

= They are mostly composed of hydrogen and helium with some amount of another elements.

= when the density of nebula decreases then they contract because of their  gravitational force and then its temperature rises at very high level and in that temperature hydrogen atom makes helium by fusion reaction and because of the speed of hydrogen atom and also heat the nebula takes a spherical shape which we call star.

Now black hole formation -

= The gravitational force of stats are balanced by their heat.

And hydrogen acts as a fuel for it.

= and when its hydrogen  finishes then with passage of  time that star cools down and then its mass and density  becomes 4 times greater then its original mass and density.

And then that star can't control its gravitational force and then a blast occurs which we call supernova.

And after this blast if any of the piece of that star which have more mass remains then it becomes a star which have mass and density of a critical level and we call this as  Neutron star.

In this type of Neutron star because of its gravitational force then it starts contracting  and after contracting it at a critical level then it becomes a body which have infinite density and mass and because of this infinte density and mass the space time bents inward there and then it doesn't be there and we call this as a black hole.

Its whole mass is focused at center which we call it

✳ central singularity point 

And the boundary of black hole is called

✳ event horizon

And nothing can escape from here even light can't.

And here concept of time doesn't work.

=>  According to theory of relativity if the object is near the black hole then the time slows down for it.

Types of black holes

1. Stellar mass black hole

~> It is the type of black hole formed because of contraction of a star which have mass about 3 times greater than the sun.

2. Super massive black holes

~> It is formed in center of any galaxy and have infinite mass and gravitational force and it has mass about 100000000 times that of sun.

3. Permordial or small black holes

~> They are formed because of the more heat at the center of a star and the mass of that star is less than that of our sun.

Physicist  think that  they formed with the beginning of universe

✳ the nearest black from earth is 

cygnus x1