Question

Why do cepheid stars pulsate?

Answer 1

Hot areas in the star produces `He^+`, even hotter areas produce `He^(2+)`.
`He^(2+)` absorbs more light than `He^+` and so absorbs more heat too.
It heats up, expands, cools and repeats.

Explanation:

Check out this link to Khans Academy for a video explaining it in more detail;

https://www.khanacademy.org/science/cosmology-and-astronomy/stellar-life-topic/cepheid-variables/v/why-cepheids-pulsate

Skip to 0:53