Disk-Disk Encounters between Low-Mass Protoplanetary Accretion Disks

Simulations of the collapse and fragmentation of turbulent molecular clouds and dense young clusters show that encounters between disk-surrounded stars are relatively common events that should significantly influence the resulting disk structure. In turn, this should alter the accretion rate of disk matter onto the star and the conditions under which planet formation occurs. Although the effects of star-disk encounters have been previously investigated, very little is known about encounters in which both stars are surrounded by disks. In this paper, encounters of such disk-disk systems are studied quantitatively. We find that for low-mass disks (M_D=0.01 M_solar) the results from star-disk encounters can be straightforwardly generalized to disk-disk encounters as long as there is no mass transport between the disks. Differences between star-disk and disk-disk encounters naturally occur when significant amounts of matter are transported between the disks. In this case we find that, although the mass distribution does not change significantly, matter caught in highly eccentric orbits is transported surprisingly far inside the disk. The captured mass partly replenishes the disk but has a much lower angular momentum. This can lead to a reduction of the angular momentum in the entire disk and thus considerably increased accretion shortly after the encounter as well as in the long term.