Final answer:
Star formation is more likely to occur in cold molecular clouds due to the inhibitory effects of high temperatures. Massive stars emit ultraviolet radiation and high-speed gas that heat the surrounding gas, causing it to expand and increasing the density necessary for star formation.
Step-by-step explanation:
Star formation is more likely to occur in cold molecular clouds than in regions where the temperature of the interstellar medium is several hundred thousand degrees. The high temperature inhibits star formation because it prevents the cloud from collapsing and reaching the high core temperature needed for nuclear fusion to occur. When a massive star is formed, it emits a large amount of ultraviolet radiation and ejects high-speed gas, which heats the gas around the stars and causes it to expand. This increase in density is necessary for stars to form in the compressed gas.