"Gravitational instability" refers to a situation where the force of gravity causes an object or system to become unstable and possibly collapse or break apart. Full definition
More importantly, these events can be linked to a period of gravitational instability in the disk. (sciencedaily.com)
Alan Boss, a theorist at the Carnegie Institution for Science in Washington, D.C., has pushed an idea called gravitational instability, in which an especially cool and massive protoplanetary disk can develop ripples that can coalesce into gas giants, with or without cores. (sciencemag.org)
Astronomers also assume that some planets in other planetary systems were formed by gravitational instability. (alma-telescope.jp)