The third and the shortest time scale is the dynamical time scale and it is the time it would take a star to collapse if the pressure supporting it against gravity were suddenly removed.

It can be estimated from the time it would take for a particle to fall freely from the stellar surface to the center. That is,

Thus, the dynamical time scale is given by

The dynamic time scale is about 30 minutes for our Sun. For other stars, the dynamical time scale is

t_d is actually sqrt(r^3 / (2GM))