  In explaining the relative metal abundances observed in galaxy groups and
clusters, it is generally assumed that all metals created by supernovae are
present either in visible stars or the hot gas. We discuss here the possibility
that some of the iron expelled into the hot gas by Type Ia supernovae may have
radiatively cooled, avoiding detection by X-ray and optical observers.
Hydrodynamic models of Type Ia explosions in the hot gas inside elliptical
galaxies result in a gas of nearly pure iron that is several times hotter than
the local interstellar gas. We describe the subsequent thermal evolution of the
iron-rich gas as it radiates and thermally mixes with the surrounding gas.
There is a critical time by which the iron ions must mix into the ambient gas
to avoid rapid radiative cooling. We find that successful mixing is possible if
the iron ions diffuse with large mean free paths, as in an unmagnetized plasma.
However, in microgauss fields the Larmor radii of the iron ions are
exceptionally small, so the field geometry must be highly tangled or radial to
allow the iron to mix by diffusion faster than it cools by radiative losses.
The possibility that some of the supernova iron cools cannot be easily
discounted.
