Russell lecture: Dark star formation and cooling instability

Optically thin cooling gas at most temperatures above 30 K will make conden sations by pressure, pushing material into cool, dense regions. This works without gravity. Cooling condensations will flatten and become planar/simil arity solutions. Most star formation may start from cooling condensations, where gravity is only important in the later stages. The idea that some of the dark matter could be pristine white dwarfs that condensed slowly onto p lanetary-sized seeds without firing nuclear reactions is found lacking. How ever, recent observations indicate 50 times more halo white dwarfs than hav e previously been acknowledged, enough to make the halo fraction observed a s MACHOS. A cosmological census shows that only 1% of the mass of the unive rse is of known constitution.