INSTABILITIES IN SELF-GRAVITATING GASEOUS DISKS

We calculate the non-linear evolution of thin self-gravitating gaseous discs with unstable non-axisymmetric normal modes. The instabilities occur when the initially axisymmetric disc is stable to axisymmetric modes. The modes can have corotation situated either inside or just outside the disc's outer boundary. The unstable modes are found to be important for redistributing the disc's mass and angular momentum on a dynamical time-scale appropriate to the outer disc. Unstable non-axisymmetric modes may be crucial in driving mass accretion on to central galactic black holes or protostars embedded by self-gravitating gaseous discs.