Life cycle of a star

Massive clouds of dust and gas(mainly hydrgen) swirl in together due to gravitational attraction.

A large ball of gas forms in the very centre of this cloud of dust and gas. 

This is called a nebula.

As the nebula gets denser, more gas is pulled in.

It gets hotter and hotter.

This is a protostar.

So much heat and pressure builds up that nuclear fusion of hydrogen occurs, this forms helium.

A star is born.

This is the main part of the cycle and usually last around 10-12billion years.

Gravity pulls inward but the energy produced from fusion pushes out against the gravity. These forces are balanced and keep the star stable.

Masses of heat and light are given off from the fusion of both hydrogen and helium.

This fusion (of helium and hydrogen) forms all the lighter elements above helium and hydrgen, like carbon and oxygen ect.
(Our sun is a going through this part of its life, it has already been 5billion years into the main sequence)

This

next

part

applies

to

small

stars;

Eventually a star starts to die.

Hydrogen starts running out because too much fusion goes on.

After fusion, the star does not have much energy so it starts to cool down.

Whilst it cools the star expands and swells into a red giant.

Soon, the outer layers break away from the nebula.

All that remains after the red giant has collapses is the white hot core.

This is the white dwarf.

Soon the white hot core begins to cool.

This is now a black dwarf.

This next part applies to big stars only;

These stages come after the main sequence stage.

Bigger stars also cool, much in the same way as a small star cools.

This forms a red super giant.

Because they are big, they can fuse heavier nuclei together.

The star the explodes in a gigantic explosion called a supernova.

This creates lots and lots of light energy.

All the elemenst heavier than iron are created here, due to more fusion.

A supernova is very dense and has a strong gravitaional field.

During a supernova, the core of the star is crushed down due to large gravitational force.

This can form a dense star called a neutron star, this type of star is made up of only neutrons.

If the star is even bigger, a black hole can be formed.

The core of the star is crushed down, this is the black hole. 

The black hole is very very small.

The gravitaional pull is so strong that nothing can escape, not even light (hence its name).