The universe is expected to have a time when star formation slowly ceases. However, this seems bizarre as there is always an abundant amount of matter in the Universe. Massive amounts of hydrogen exists in several galaxies, but they are deemed dead. Any gravitational disturbance can send the gas into a protostar, and even if there weren't hydrogen left, enough helium or carbon can turn a star into a star that fuses heavier elements, until the universe is depleted of such and mostly elements heavier than iron.
So why does star formation cease when these is still abundant hydrogen around? Is there some sort of interaction in these hydrogen supplies that prevents star formation? Is the gas kept at a temperature that is too hot for formation? Or have I made a misconception?