Gravitational collapse

Try to jump so high that you fly right off of the Earth into outer space. What happens? Why don't you get

very far? The gravitational force pulls you back down again very quickly. You could jump much higher on

Mars, still higher on the moon, because they're both less massive than the Earth. The strength of gravity at

the surface of the moon is only 1/6 the strength of gravity at the surface of the Earth.

You are essentially trapped on Earth, unless you can find a rocket that can travel at escape velocity away

From the Earth. This is how our space program works. If you shoot something fast enough, it can escape

Gravity and make it to outer space.

But hold the phone -- there's supposedly a maximum speed in the Universe, the speed of light. What

happens if the escape velocity of a planet were greater than the speed of light? In other words, what if

gravity were strong enough to trap light itself?

Then you'd have yourself a black hole. A black hole is a gravitating object whose gravitational field is so

Strong that light cannot escape. The event horizon is where light loses the ability to escape from the black

Hole. Nothing that goes inside the event horizon can ever get back out again, not even light.

Black holes can be created by the gravitational collapse of large stars that are at least twice as massive as

Our Sun. Normally, stars balance the gravitational force with the pressure from the nuclear fusion

Reactions inside. When a star gets old and burns up all of its hydrogen into helium and then turns the

Helium into heavier elements like iron and nickel, it can have three fates. The first two fates occur for stars

less than about twice the mass of our Sun (and one of them will be our Sun's eventual fate). These two fates

Both depend on the fermionic repulsion pressure described by quantum mechanics -- two fermions cannot

Be in the same quantum state at the same time. This means that the two stable destinies for a collapsing star

will be:

A white dwarf supported by the fermionic repulsion pressure of the electrons in the heavy atoms in the

Core

A neutron star supported by the fermionic repulsion pressure of the neutrons in the nuclei of the heavy

Atoms in the core

If the mass of the collapsing star is too large, bigger than twice the mass of our Sun, the fermionic

Repulsion pressure of either the electrons or the neutrons is not strong enough to prevent the ultimate

Gravitational collapse into a black hole.

The estimated age of the Universe is several times the lifespan of an average star. This means there must

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