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Second Collapse

For $10^{-7.5}{\rm g cm^{-3}}\mbox{\raisebox{0.3ex}{$<$}\hspace{-1.1em}
\raisebox{-0.7ex}{$\sim$}} 10^{-2.5}{\rm g cm^{-3}}$, the exponent becomes $\gamma=1.1$. In this density range of $\rho \mbox{\raisebox{0.3ex}{$>$}\hspace{-1.1em}
\raisebox{-0.7ex}{$\sim$}} 10^{-7.5}{\rm g cm^{-3}}$ the temperature exceeds $10^3$K. Due to this temperature, the hydrogen molecules begin to dissociate and the dissociation process absorbs the energy. By this, gas becomes much softer ( $\gamma\rightarrow 1$) than the first core. This introduces another dynamical contraction, the second collapse (points number 6-7 of Figure 4.13).

Kohji Tomisaka 2007-07-08