Expert: Jayendra Upadhye - 4/9/2008

Question
If a star becomes a red giant when all its hydrogen is used up and later become a nebula, how can a new star form without hydrogen?

Answer
Hi,
There is a churning process going on in the convective zone deep inside stars. In this area, some helium and a lot of hydrogen from the core, constantly goes up and down.

When the helium flash occurs, the star looses 30% of its mass in a violent solar wind. At that time hydrogen too is lost.

That hydrogen mingles with interstellar hydrogen and in due course (along with other heavier debri), creates another 2nd / 3rd generation star (populations 1).

The sun is a 3rd generation star.

New stars form when supernova shock waves propagate thru nearby existing clouds of dense cool gas. Some of which came from that mass loss from the smaller star that underwent a red giant phase.

hope that suffices.
regards
Jayen