Paul Taylor asked:
I understand the sun gets its power from hydrogen fusion and gradually fusing together bigger and bigger atoms. Towards the end of its life and particularly if it goes supernova it blasts all of the heavier elements out into the surrounding space. Iíve often heard it said itís what feeds the next generation of stars. Is it the spent star fuel that goes on to create the new star?
We put this question to Chris Davis:
It certainly happens if you burn hydrogen to form helium the star is the consequence of an equilibrium of forces. Youíve got the gravitational collapse of that body of gas, pulling inwards on it and heat generated by the nuclear reaction in it pulling the star out. Youíve got to have an intense amount of pressure in the middle to force hydrogen nuclei close enough together to form helium. There are various other burning cycles. You can burn helium to produce carbon but eventually when all the fuel is used up in the core there is no forcing out of the star. Gravity wins out and it collapses the star in on itself. When this happens, very briefly you get a large increase in density in the starís core. That can generate these much heavier elements and then the star will explode.
Chris - So you can look at it as the stars are the uteruses of the universe, they give us everything that weíre made of?Chris D - Thatís true. The star isnít going to be completely burned to the other element. There is going to be a large amount of hydrogen. Also, the universe is still very much dominated by hydrogen gas which is the primal fuel for stars. That dust, that matter, the heavier elements will be spread out into space. Some of it will contaminate the next generation of stars. As another cloud starts to collapse together under its own [gravity] youíll get some of that heavier element polluting, if you like, the new star thatís formed. It wonít be pure hydrogen to start with and youíll still have the majority of the gas will be hydrogen but with the heavier elements surviving.