According to the Wikipedia article Elliptical galaxy, elliptical galaxies have a much lower concentration of gas between the stars than spiral galaxies. I know that until the gas is below a certain concentration, its atoms don't travel very far between collisions and it follows the normal gas laws and the gas actually flows into the stars when they pass by. I know that when the interstellar gas is at such a low concentration that atoms on average travel a much larger distance than the average diameter of a star in the elliptical galaxy it's in, the gas doesn't follow the normal gas laws and gas gets mainly absorbed into stars by happening to be headed towards one and colliding with it rather than by flowing towards one and the ratio of the rate of absorption of gas into stars to the concentration of interstellar gas is lower, and a star has about the same expected time before colliding with another star as an interstellar gas atom has before colliding with a star. I also know that when the interstellar medium is at the equilibrium concentration, there are 3 possible driving forces for the reduction of interstellar gas; star formation, flow of interstellar gas into stars, and random collisions of interstellar gas atoms with a star which can only occur at very low concentration; and 2 driving forces for the increase in interstellar gas, the slow escape of gas molecules from stars and collisions between stars because collisions occur at a high enough speed to produce an explosion instead of combining into a larger star. Which driving force for the reduction of interstellar gas is the largest? Also, which driving force for the increase in interstellar gas is larger? If it's star formation, that means the interstellar gas is at a high enough concentration to follow the normal gas laws but since the amount of interstallar gas is at equilibrium, the main driving force for the increase in interstellar gas is collisions between stars. If it's the slow escape of gas from stars, the main driving force for the decrease in interstellar gas could be the flow of gas into stars or the random collisions of gas molecules with stars but not star formation. If the main driving force for the reduction in interstallr gas concentration is collisions of gas molecules with stars, then a star has about the same expected time beofre a collision with another star as an intersteller gas atom has before colliding with another star so the expected time before a star collides with another star is less than the age of the galaxy and if it's flow of gas into stars, the main driving force for the increase in interstellar gas could be either of the two driving forces but if the driving force for the increase is collisions between stars, the expected time before a star collides with another star is less than the age of the galaxy,
On the other hand, if the interstellar gas concentration has not yet reached equilibrium, it could be that not enough time has gone by for the interstellar gas to not follow the normal gas laws and star formation occurs mainly by the gas coalescing into stars. It could also be that the interstellar gas started diving exponentially until it stopped following the normal gas laws then the rate at which it divides exponentially greatly reduced so it has not yet had time to reach the equilibrium concentration.