The recent research domain of asteroseismology refers to the study of the internal structure of pulsating stars through the interpretation of their frequency spectra. Asteroseismologists make great use of the oscillations to probe the stellar interior, which is not directly observable. The basic principles of asteroseismology are very much alike those developed by earth seismologists.
No part of the Universe is more difficult to observe directly than the interior of the stars. The reason why stellar interiors can be probed from oscillations is that different oscillation modes penetrate to different depths inside the star. Asteroseismology is the only available method so far to derive the internal structure of the stars with high precision.
Oscillations can be excited in stars when thermal energy is converted into kinetic energy of pulsation. Similarly as for any heat engine, this proces is effective if heat is absorbed in the high temperature phase of oscillation and emitted when the temperature is low. The main mechanism for stars is the net conversion of radiation energy into pulsational energy in the surface layers of some classes of stars. The resulting oscillations are usually studied under the assumption that they are small, and that the star is isolated and spherically symmetric.
