= Cataclysmic-variable period minimum
{title2=$P_{\min}$}
For a <Roche lobe>-filling donor with local radius response $R_2\propto M_2^\zeta$, the <Roche-lobe-filling period-density relation> gives $P\propto M_2^{(3\zeta-1)/2}$. As mass is lost, the period falls for $\zeta>1/3$ and rises for $\zeta<1/3$, with a minimum at the transition. The reversal is called a period bounce. Slow evolution near the turning point produces an accumulation in the period distribution: for a steady flow of systems along one evolutionary branch, $N(P)\propto1/|\dot P|$.
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