Theory of the radial-orbit instability as a universal cause of structure formation in stellar systems
Polyachenko V. L.
An analytic theory is derived for a basic instability of collisionless gravitating systems: the radial-orbit instability. Radial orbits arise in a natural way upon (for example) the formation of galaxies during the collapse of a stellar cloud from an initial state with an extremely low density. The theory shows that the instability occurs if the gravitational potential of the system leads to a precession of orbits with small angular momenta in the direction in which the stars are revolving in these orbits.