There are two main types of galaxies: «blue», star - forming galaxies and «red and dead» galaxies that no longer form new stars. (newscientist.com)
In space, they gather in clouds of dust and gas, which form new stars, and for each generation of new stars, more elements are formed. (sciencedaily.com)
We know that star formation involves gravitational collapse, but in - fall motions forming a new star have yet to be found. (almaobservatory.org)