We have examined the evolution of astrophysical disc models for which the temperature decreases as a function of radius, leading to an angular velocity profile that varies with both radius and height. This work demonstrates for the first time that growth of the vertical shear instability in discs leads to a sustained turbulent flow whose associated Reynolds stress leads to outward angular momentum transport. The results may have application to the outer regions of proto-planetary discs, influencing mass accretion and the formation of planets.
We have examined the migration of low mass planets embedded in magnetized discs with a layered structure consisting of turbulent regions near the surface, and a non-turbulent “dead zone” near the disc midplane. A planet migrates because it experiences a net torque with two contributions: a Lindblad torque that drives inward migration; a corotation torque that slows or reverses migration. Our results show for the first time that the corotation torque in a dead zone is ineffective, with the implication being that low mass protoplanets will migrate rapidly as they grow to become super-Earths or Neptune-like planets. A paper describing these results is in preparation.