For 10 points, what is this process by which small clusters of stars and dust come into being and become large?
"Violent relaxation" occurs in the final step of this process when the orbits of individual objects become random. A discredited "top-down" model for this process assumes that a homogeneous gas cloud collapses uniformly, which is inconsistent with observations of characteristic R-process spectral lines in the thin disk and halo that imply the latter is older. One phenomenon that drives this process creates tidal streams and polar rings, and that phenomenon is one candidate explanation for (*) lenticulars. One instance of the final stage in this process will occur in approximately 3.4 billion years, when the disks of Andromeda and the Milky Way are repeatedly disrupted and the two merge into a giant elliptical. For 10 points, what is this process by which small clusters of stars and dust come into being and become large?
"Violent relaxation" occurs in the final step of this process when the orbits of individual objects become random.
galaxy formation or galactic evolution [accept synonyms and word forms; accept "galactic merger" before "top-down."]