About the size of the Earth but can be more massive than the Sun. Most massive stars leave behind neutron stars and black holes, going through the supernova stage in some cases. Pulsating variables are of interest not just to stellar astronomers but extragalactic astronomers as well. Power being created in core is not always equal to power being emitted from surface. Atmosphere too opaque to radiation energy and hence pressure builds up outer layers expand as they heat up atmosphere becomes too transparent as it expands energy escapes too quickly star contracts again but contracts too much repeat ad nauseum Star contracts and expands over and over, changes in luminosity periodically.
Periods range from hours to years.
Whole strip on H-R diagram where stars are unstable like this. Cepheid variables have a close correlation between their period and their luminosity . This is the best way for finding distances to other galaxies.