How do stars like ours form and die?

Stars are born when gases at high pressure and temperatures begin to burn. They start life out as a big cloud of space junk and debris. Slowly, there's a bit of the cloud with more stuff in it than the other bits so it has a bit more gravitational pull and so slowly, the rest of the cloud gets pulled towards that general area.

But as more of the gas collects there, then there are even more gravitational forces acting so pressure increases and more elements continue to get pulled in. Pressure rises causes the temperature to rise and, once it's hot enough, hydrogen undergoes a nuclear fusion to form helium. This releases energy making it hotter and increases pressure. It also starts a chain reaction so more fusion occurs.

The star can then settle down to a long stable slog with gravity pulling things in balancing with the fusion pressure pushing things out. So there's not much growth and not much really happens. The star is known as a main sequence star. This is the stage our sun is at.

Eventually, however, all good things come to an end and there's no more hydrogen left. So fusion starts to happen with larger elements like helium. Stars like ours expand to become red dwarfs and become hotter. When our sun does this, it will expand to destroy the Earth.

When all the nuclear reactions are done, there's no outward pressure keeping the star big so gravity causes it to collapse into itself forming a white dwarf. Also, no reactions mean no energy so things begin to cool off a bit. And that’s that. Over billions of years, our sun has gone from a cloud to the sun we know and love and will eventually expand to destroy our planet before falling into itself and turning cold. 

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