The interiors of stars are largely mysterious regions because they are so difficult to observe directly. Our lack of understanding about the physical processes there, like rotation and the mixing of hot gas, introduces considerable ambiguity about how stars shine and how they evolve. Stellar oscillations, detected through brightness fluctuations, offer one way to probe these subsurface regions. In the Sun, these vibrations are due to pressure waves generated by turbulence in its upper layers (the layers dominated by convective gas motions). Helioseismology is the name given to the study of these oscillations in the Sun, and astroseismology is the term used for other stars.
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Source: Phys.org