It is all about these modes propagating in the interior of the Sun. The pressure modes (or p modes) propagate in the convective and radiative zone and seem to avoid the very core of the Sun. The gravity modes (or g modes) propagate in the radiative zone and by tunnel effect in the convection zone where they are heavyly damped. The p modes have enabled helioseismologists to recover the internal structure and dynamics of the Sun down to below the radiative zone. The blind spot is still the solar core that could be probed with the g modes, yet to be discovered. The figure here below shows how the p mode and g modes propagate in the Sun (respectively A, B)