The Universe At Large 003 - Nuclear Fusion
22 Nov 2015Undomyr
THE UNIVERSE AT LARGE 003 - Nuclear Fusion Hello and welcome back to The Universe At Large, it has been a while since the last post and my apologies for this.
So without further ado, let's get to the science. Today's topic being nuclear fusion as found in stars.
All stars need some form of energy to make them shine and burn. The stars on the "main-sequence", that is, healthy, common stars of the O B A G K M -classes, get this energy from nuclear fusion.
Fusion is the simple concept of taking two atoms and forcing them together with such force that they become a single larger atom. Stars are heavy enough that they reach pressures in their core where the atoms are so close together that the energy from their extreme temperatures is enough to achieve this.
The most common example being the fusion of two hydrogen atoms, 2 H to form one helium atom, He. In a chemical formula this would be;
2 H -> He
Let's take Sol, our home star, as an example of this. The Sun is a small G-class star, that fuses hydrogen to helium.
This gives enough energy to make life on earth possible, but not so much it strips away our atmosphere or irradiate the surface too much.
The fusion taking place in the sun requires only a little energy to be sustained, producing much more than is required to make 2 atoms of hydrogen fuse. As long as there is enough energy to make even 1 fusion take place, the entire chain reaction will continue.
As hydrogen gets turned into helium the star gets bigger and slowly becomes less energetic. The outer surface of the star expands, the helium pushing it outward as more and more of it builds up.
Eventually the fusion of hydrogen stops, as there is not enough left of it to sustain a chain-reaction of fusing hydrogen atoms. Depending on the size of the star it will then either start fusing Helium into other atoms or, as is the case with smaller stars like the sun, will expand rapidly, burn away the last of its hydrogen and then cool off rapidly.