The Effects of Metallicity and Grain Size on Gravitational Instabilities in Protoplanetary Disks

Observational studies show that the probability of finding gas giant planetsaround a star increases with the star's metallicity. Our latest simulations ofdisks undergoing gravitational instabilities (GIs) with realistic radiativecooling indicate that protoplanetary disks with lower metallicity generallycool faster and thus show stronger overall GI-activity. More importantly, theglobal cooling times in our simulations are too long for disk fragmentation tooccur, and the disks do not fragment into dense protoplanetary clumps. Ourresults suggest that direct gas giant planet formation via disk instabilitiesis unlikely to be the mechanism that produced most observed planets.Nevertheless, GIs may still play an important role in a hybrid scenario,compatible with the observed metallicity trend, where structure created by GIsaccelerates planet formation by core accretion.