wolram said:
I will not question your knowledge, but were is, "out of bounds", for star
formation? and why ?
If it remained bound to the galaxy, then given enough time, I would expect the vast majority of gas to end up in either stars, black holes, or some other compact object. It's certainly true that a hot gas will not be able to immediately collapse to form stars, but gas cools and the galaxy is not a closed system, so it would not remain hot forever.
However, note that I specified that the gas remain bound. Energy input from supernovae can sometimes provide enough of a "kick" to allow the gas to escape the galaxy and, perhaps, the local group or cluster. It then becomes dispersed in the surrounding medium. Now one might suspect that the same arguments apply there as to inside the galaxy; that is, the gas will eventually cool and collapse. However, there is another factor to consider -- the expansion of the universe. In a traditional cold dark matter universe (minus dark energy), structure formation continues as long as the expansion does and everything will eventually become incorporated into a gravitationally bound entity. However, a universe with, say, a cosmological constant, will cease forming structures on some specific physical scale. If the "dark energy" in our universe really is a cosmological constant, then this scale will be about that of galaxy clusters (~100 Mpc).
What does this mean? Well, basically, if you can succeed in dispersing the gas over scales greater than that which can gravitationally collapse, presumably you can prevent that gas from ever forming stars. We certainly do observe gas dispersed over those scales, but we are still unsure about how much of it is primordial and how much was ejected from galaxies.
