Star Summary
The most important factor in the evolution of a star is its mass.
Stars originate from nebulae (clouds of dust and gas).
Nebulae collapse to form a single mass because of the force of their particles' gravity.
A star in its first stage of development is called a protostar.
Stars normally produce heat and light by fusing hydrogen into helium. (Stars that do this are called main sequence stars.)
When a main sequence star's core starts to run out of hydrogen it expands and cools to become a red giant.
A red giant's core turns slowly into iron.
Red giants of up to ten times the mass of the Sun become white dwarfs.
A white dwarf is a small hot star about the size of the Earth.
Red giants of over ten times the mass of the Sun explode in a supernova.
A supernova is an exploding star.
If a red giant's core survives a supernova, it ends up either as a neutron star or a black hole.
Neutron stars are made of neutrons.
A neutron star spins and emits a beam, rather like a lighthouse.
Neutron stars are sometimes called pulsars because we receive their emissions in pulses.
A black hole is the core of a red giant which has collapsed into a single point called a singularity.
A black hole's gravity is of such strength that nothing can escape it - not even light.
It seems that every galaxy has a black hole at its centre.
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