The role of multiplicity in disk evolution and planet formation

Abstract

The past decade has seen a revolution in our understanding of protoplanetary disk evolution and planet formation in single-star systems. However, the majority of solar-type stars form in binary systems, so the impact of binary companions on protoplanetary disks is an important element in our understanding of planet formation. We have compiled a combined multiplicity/disk census of Taurus-Auriga, plus a restricted sample of close binaries in other regions, in order to explore the role of multiplicity in disk evolution. Our results imply that the tidal influence of a close (≲40AU) binary companion significantly hastens the process of protoplanetary disk dispersal, as 2/3 of all close binaries promptly disperse their disks within ≲1Myr after formation. However, prompt disk dispersal only occurs for a small fraction of wide binaries and single stars, with 80%-90% retaining their disks for at least 2-3Myr (but rarely for more than 5Myr). Our new constraints on the disk clearing timescale have significant implications for giant planet formation; most single stars have 3-5Myr within which to form giant planets, whereas most close binary systems would have to form giant planets within ≲1Myr. If core accretion is the primary mode for giant planet formation, then gas giants in close binaries should be rare. Conversely, since almost all single stars have a similar period of time within which to form gas giants, their relative rarity in radial velocity (RV) surveys indicates either that the giant planet formation timescale is very well matched to the disk dispersal timescale or that features beyond the disk lifetime set the likelihood of giant planet formation.