Variable stars
K mechanism
K-mechanism
κ-mechanism
Kappa mechanism
Luminosity classification
A process based on the effects of opacity (κ) that drives the pulsations of many types of variable stars. Consider a layer of material within a star and suppose that it undergoes inward contraction. This inward motion tends to compress the layer and increase the density. Therefore the layer becomes more opaque. If a certain amount of flux comes from the deeper layers it gets stuck in the high κ region. The energy accumulates and heat builds up beneath it. The pressure rises below the layer, pushing it outward. The layer expands as it moves outward, cools and becomes more transparent to radiation. Energy can now escape from below the layer, and pressure beneath the layer diminishes. The layer falls inward and the cycle repeats. The κ mechanism is believed to account for the pulsations of several star families, including Delta Scuti stars, Beta Cephei variables, Cepheids, and RR Lyrae stars.