Question: what are stars?

Andrew McKinley answered on 18 Nov 2014:

Stars are basically enormous nuclear furnaces! Easiest way to explain is to try to imagine how a star forms:

How to make a star:
1) Get some hydrogen.
2) No, really, you’re going to need a *lot* of hydrogen
3) Put it all in close proximity – eventually the hydrogen will start to stick together and form clumps
4) These clumps will have their own microgravity. They will start to form clumps of clumps
5) Eventually this process will accelerate – this is called “accretion”
6) Once enough gas has clumped together it pulls in all the gas around it and the mass of the clump increases as all the gas lands onto the clump. (note – the gas is not yet “burning”)
7) All this gas coming together starts to heat up, and the ‘weight’ of it compresses the gas at the core
8) More gas, more compression
9) Eventually, the compression – and heat – is such that at the core, two hydrogen nuclei (two protons) get close enough together, and suddenly they fuse together (a fusion reaction)
10) BANG! This ‘spark’ releases a huge amount of energy, and triggers even more fusion reactions. This massive release of energy causes the ball of gas to expand, until the expansion force balances the gravitational force. The nuclear fusion process continues as long as there is a plentiful supply of nuclei to fuse together. With 2,000,000,000,000,000,000,000,000,000,000 kg of hydrogen, it should keep us going for a while (about 9 billion years or so!)

Once we reach this point, we have a star!