One of the biggest puzzles in astrophysics is the process that turns this very diffuse, hot and cold gases and dust in the ISM into stars. To the upper left of center is the evolved blue supergiant called Sher 25. Near the center is a starburst cluster dominated by young, hot stars. Dark clouds at the upper right are so-called Bok globules, which are probably in an earlier stage of star formation. Processes that heat the ISM are fairly well understood.
Stellar winds blow through galaxies, transferring huge amounts of energy.
Massive stars explode as supernovae shortly after their formation, stirring and heating the gas out of which they formed. These injections of energy from supernovae and stellar winds profoundly affect the ISM and determine the rate at which new stars form. The energy in the gas causes the clouds to glow in bright colors. However, even after decades of study, the process by which this diffuse gas in the ISM cools and influences the star formation remains one of the enduring puzzles of astrophysics . In order to understand how stars form , it is necessary to understand how this extremely hot gas cools.