What is the study of asteroseismology? Why do astrophysicists study this field?
Oscillations (waves) crossing the surface of the star tell us about the density of the medium they are travelling through.
When we observe a star close up (the Sun is our only example here) we can see oscillations crossing its surface. These are caused by flares and other phenomena to such an extent that the Sun's surface appears to be a roiling mass of superheated gas (unsurprising, eh?)
The speed and alteration in the direction of the wave's travel gives us information about the density and temperature of the medium through which it is travelling.
The ESA had a satellite observing this (and other) effects for many years called SOHO which made several profound discoveries, including the waves you refer to. There are many good videos on YouTube, but I'd suggest this (specifically around 43 or 44 minutes in)