For a star, the dynamical time scale is defined as the time that would be taken for a test particle released at the surface to fall under the star's potential to the centre point, if pressure forces were negligible. In other words, the dynamical time scale measures the amount of time it would take a certain star to collapse in the absence of any internal pressure. By appropriate manipulation of the equations of stellar structure this can be found to be
where R is the radius of the star, G is the gravitational constant and M is the mass of the star. As an example, the Sun dynamical time scale is approximately 2250 seconds. Note that the actual time it would take a star like the Sun to collapse is greater because internal pressure is present.
The 'fundamental' oscillatory mode of a star will be at approximately the dynamical time scale. Oscillations at this frequency are seen in Cepheid variables.
Read more about this topic: Dynamical Time Scale
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