S7 - Hydrostatic core

Question 1

What happens at the end of the initial collapse of a molecular cloud?

Answer 1

A hydrostatic core (5au diameter) develops with a shock front at the interface between the core and an outer envelope of in-falling material.

Question 2

How many degrees of freedom do monatomic gases have?

Answer 2

Only 3 (only translational) as there are no bonds to rotate about.

Question 3

What happens to the hydrostatic core created by fragmentation over time?

Answer 3

As the temperature and density of the hydrostatic core increases due to accretion of material, a point will be reached at which its molecules and dust will become so energetic that they will dissociate (molecule → atoms). Every molecular hydrogen dissociation event absorbs energy, reducing the thermal pressure inside the hydrostatic core causing it to become dynamically unstable and a second collapse occurs. Hydrostatic equilibrium is re-established when the core radius reaches about 2 solar radii, halting the core collapse. A second shock front is established as the envelope continues to accrete infalling material.