A SN blast-wave shock (or stellar wind) moves out to
meet the surrounding cooler ISM which is heated to high temperatures by shock
waves.
Conductive Heating
If a million degree hot gas is in contact with a cold,
dense gas cloud heat will flow from the hot to cold gas by conduction, which
then becomes warmer and expands into the hot gas.
Turbulent Heating
As a hot gas shears across a cold gas-cloud boundary it
can generate small-scale eddies of ‘warm” gas. This is generally referred to
as a “turbulent mixing layer”
