Dust and gas density evolution at a radial pressure bump in protoplanetary disks

Abstract

We investigate the simultaneous evolution of dust and gas density profiles at a radial pressure bump located in a protoplanetary disk. If dust particles are treated as test particles, a radial pressure bump traps dust particles that drift radially inward. As the dust particles become more concentrated at the gas pressure bump, however, the drag force from dust to gas (back-reaction), which is ignored in a test-particle approach, deforms the pressure bump. We find that the pressure bump is completely deformed by the back-reaction when the dust-to-gas mass ratio reaches ∼1 for a slower bump restoration. The direct gravitational instability of dust particles is inhibited by the bump destruction. In the dust-enriched region, the radial pressure support becomes ∼10−100 times lower than the global value set initially. Although the pressure bump is a favorable place for streaming instability (SI), the flattened pressure gradient inhibits SI from forming large particle clumps corresponding to 100−1000 km sized bodies, which has been previously proposed. If SI occurs there, the dust clumps formed would be 10−100 times smaller, that is, of about 1−100 km.

Planetesimal formation by an axisymmetric radial bump of the column density of the gas in a protoplanetary disk

“…In our simulation, the dust clumping proceeds significantly around the null points of the radial pressure gradient x ± , in contrast to the simulation of Taki et al (2016). Because Taki et al (2016) did not include the effect of the vertical gravity, dust density did not increase around the region where the radial pressure gradient is almost zero.…”

“…We assume τ s = 0.01, which corresponds to cm-sized particles in the asteroid region of Hayashi's model. We defined an initial gas density with a radial density bump identically to Taki et al (2016) as follows:…”

“…This study differs from that of Taki et al (2016) because we take the vertical component of the stellar gravity into account. We compare our results with those of Taki et al (2016) and discuss the causes of the differences.…”

“…Recently, Taki et al (2016) performed a numerical simulation of dust and gas with an initially defined pressure bump. They showed that the initially defined pressure bump evolves to become a region where the radial pressure gradient is almost zero.…”

“…They concluded that the streaming instability that is excited by the relative velocity of dust and gas would be difficult to grow and a pressure bump will not promote planetesimal formation. However, Taki et al (2016) omitted two important effects: (1) non-axisymmetric vortices caused by the Rossby wave instability (Li et al 2000;Lyra and Mac Low 2012;Meheut et al 2012a, b;Lin 2012;Ono et al 2016) and (2) the component of stellar gravity vertical to the midplane of the disk.…”