Spiral shocks in astrophysical disks

Spiral shocks waves are present in many astrophysical systems, including galactic disks, binary systems such as cataclysmic variables, AGN disks, and are probably present in disks around newly forming stars. In this paper we will discuss, in particular, spiral shocks resulting from the growth of a gravitational instability. We investigate how these spiral waves can transport angular momentum outwards and mass inwards - an important aspect of star formation - and a process that may play a role in the secular evolution of disk galaxies, leading to the formation of bulges. In some cases the instability can be sufficiently violent for the disk to fragment into gravitationally bound objects. This may explain the origin of the stellar population orbiting the galactic center, and has also been suggested as a mechanism for forming gaseous planets similar to Jupiter and Saturn. We consider the conditions required for fragmentation and whether such a process could indeed produce gaseous planets.