What causes pulsating variable stars to pulsate?
Intrinsic pulsating stars are stars that, by some means, change their brightness in a periodic, or even irregular way, over a span of hours to hundreds of days. The short period variables are typically hotter stars in classes A – K, while the long period variables are older, cooler stars of class M. Betelgeuse, in Orion for example is a semi-regular, long period variable whose brightness changes over a time of several hundred days. It is a red super giant star. Delta Cephi, the archetype for the Cepheid variable star, is a short period variable with a period of 5.37 days. The brightness of a star depends on its temperature and its radius. In fact the luminosity varies as the square of the radius and the fourth power of the surface temperature. This means that there are two effects that contribute to making a star’s brightness change, both determined by the dynamics of a star’s internal structure. If you change the radius of the star by 10 percent, the luminosity of the star will increa
