Thermally driven spontaneous dust accumulation in the inner regions of protoplanetary disks

Abstract

In protoplanetary disks, the formation of planetesimals via streaming and/or gravitational instabilities requires regions with a locally enhanced dust-to-gas mass ratio. Conventionally, gas pressure maxima sustained by gas surface density maxima have been considered as the primary cause of such dust accumulation. However, the disk's pressure structure depends not only on gas density but also on the temperature structure, which itself is influenced by the distribution of dust. In this study, we propose a novel mechanism for dust accumulation, which is driven by the coevolution of dust and disk temperature. In the inner disk region where the midplane temperature is primarily determined by the balance between viscous heating and radiative cooling, a perturbation in dust surface density distribution may affect radiative cooling efficiency, potentially producing a local maximum in the temperature and pressure profiles. To test this hypothesis, we perform coupled calculations of dust and disk temperature evolution, incorporating the advection, diffusion, coagulation, and fragmentation of dust particles along with viscous heating, radiative cooling, and radial thermal diffusion. Our results demonstrate that a pressure maximum formed by a perturbation in the dust surface density can spontaneously induce dust accumulation, even in the absence of a gas surface density maximum, under conditions where dust drift is significantly faster than diffusion and the thermal evolution occurs faster than the inward migration of dust. This mechanism requires viscous heating to dominate disk heating, and typically occurs interior to the snow line. In this spontaneous dust trap, the dust-to-gas density ratio at the midplane can exceed unity, suggesting the potential for rocky planetesimal formation via streaming and gravitational instabilities.