Vortices in protoplanetary disks

We use a high-order accuracy spectral code to carry out two-dimensional, time-dependent numerical simulations of vortices in accretion disks. In particular, we examine the stability and the lifetime of vortices in circumstellar disks around young stellar objects. The results show that cyclonic vortices dissipate quickly, while anticyclonic vortices can survive in the flow for hundreds of orbits. When more than one vortex is present, the anticyclonic vortices interact through vorticity waves and merge together to form larger vortices. The exponential decay time tau of anticyclonic vortices is of the order of 30-60 orbital periods for a viscosity parameter alpha approximate to 10(-4) (and it increases to tau approximate to 315 for alpha = 10(-5)), which is sufficiently long to allow heavy dust particles to rapidly concentrate in the core of anticyclonic vortices in protoplanetary disks. This dust concentration increases the local density of centimeter-sized grains, thereby favoring the formation of larger scale objects that are then capable of efficiently triggering a state of gravitational instability. The relatively long-lived vortices discussed here may therefore play a key role in the formation process of giant planets.