Question

What causes the pulsation of a cepheid-type variable star?

Answer 1

Expansion=Contraction. Contraction=Expansion.

Explanation:

Stars entering and leaving the cephied variable stage can briefly (on a scale of a star's life) create the conditions necessary to pulsate. The Cephied Variable stage is between the Horizontal Giant Branch and the Asymptotic Giant Phase in a sun like star's life. In ordinary stars, hydrostatic equllibrium diminishes these pulsations.

Basically, Starr's in this stage can create conditions that trap their radiated energy in the outer layers. The pressure increases enough so that the outer layers expand. Therefore, the outer layers are less dense and hot, so gravity compresses the star. The process repeats.

Sorry for any bad spelling.