Answer to Question #173610 in Astronomy | Astrophysics for ANJU JAYACHANDRAN

Question

2b) Explain helioseismology. How does it help in understanding the internal structure

of the Sun?

Answer 1

Helioseismology helps us to study the structure and dynamics of the Sun through investigation of its oscillations.

Let us cite en.wikipedia.org:

"Solar oscillation modes are interpreted as resonant vibrations of a roughly spherically symmetric self-gravitating fluid in hydrostatic equilibrium."

There exist pressure modes (p modes):

"All the solar oscillations that are used for inferences about the interior are p modes, with frequencies between about 1 and 5 millihertz"

There also exist gravity modes (g modes):

"Gravity modes are confined to convectively stable regions, either the radiative interior or the atmosphere. The restoring force is predominantly buoyancy, and thus indirectly gravity, from which they take their name. They are evanescent in the convection zone, and therefore interior modes have tiny amplitudes at the surface and are extremely difficult to detect and identify."

And there are surface gravity modes (f modes):

"Surface gravity waves are analogous to waves in deep water, having the property that the Lagrangian pressure perturbation is essentially zero."

The oscillation frequencies are related to pressure, angular velocity and magnetic field, so we may determine these parameters.

The propagation of the modes depends on the structure of the Sun, so we may determine the age of the Sun through analysis of the oscillations.

Also the helioseismic observations reveal an inner uniformly rotating region and a differentially rotating shell of the Sun, roughly corresponding to the radiant zone and the convective zone.

We also may examine the properties of solar active regions by means of local helioseismology.