Schematic of the propagation of acoustic waves
in the Earth from an earthquake. A similar
situation occurs in the Sun, and so we use
helioseismology to study the solar interior.
(source: BGR)

Our Sun rings like a bell, as it is filled with acoustic waves excited by turbulent convection. These waves can be used to "see" into the solar interior using a technique called helioseismology. A useful analogy is Earth seismology. When an earthquake occurs, acoustic "sound" waves generated at the source travel deep into the Earth's interior and refract back towards the surface, where they are subsequently measured by seismographs. Comparisons of the observed travel times and amplitudes of the waves with theoretical models of the expected values allow geophysicists to infer sub-surface properties.

The situation is very similar in the case of the Sun. Waves are continuously excited and travel throughout the solar interior, some even all the way to the core. They then are refracted back to the surface where they can be measured using ground- and space-based telescopes. The information in the waves tells us about flows, sound speed, chemical abundances, asphericity, and magnetic fields along the areas where the waves travelled.

Helioseismology has given us fascinating insights about the structure of the Sun and, consequently, other stars as well. For example, we have learned about this, this, and that.

Important questions

The most important unsolved problem in solar physics concerns the generation and evolution of magnetic fields.

The future

The ultimate goal of helioseismology is to make three-dimensional spatial maps of the entire solar interior of all relevant internal properties over time. How close we can approach this depends on advances in theoretical techniques and high-quality data.