= Impulsive disruption by stellar mass loss
{title2=$E'=|W|f(1/2-f)$}
Take an initially isolated virialized self-gravitating <stellar population> with <kinetic energy> $T=|W|/2$ and <Newtonian gravitational potential energy> $W<0$. Instantaneous spatially uniform removal of mass, without kicks to surviving material, leaves fraction $f$ with $T'=fT$ and $W'=f^2W$. Hence $E'=|W|f(1/2-f)$: the homologous whole-system energy is negative only for $f>1/2$. Positive whole-system energy does not forbid a bound core after selective escape, and slow mass loss follows the <adiabatic mass-loss expansion law> instead.
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