= Negative heat capacity
{title2=$dE/dT<0$}
A decrease in equilibrium <temperature> when the total <energy> increases along a specified family of equilibria. A virialized nonrelativistic self-gravitating <ideal gas> has $E=-U$ and $U$ proportional to its particle-weighted mean <temperature>, producing this behavior. It does not mean the local gas parcel has negative heat capacity at fixed volume. It occurs naturally for isolated gravitational systems rather than stable ordinary canonical equilibrium with an infinite heat bath.
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