Accretion bursts in young intermediate-mass stars make planet formation challenging

TL;DR

This study uses magnetohydrodynamics simulations to explore how accretion bursts in young intermediate-mass stars disrupt dust accumulation and planetesimal formation, potentially explaining the scarcity of planets around such stars.

Contribution

It demonstrates that episodic MRI-driven accretion bursts hinder planetesimal formation in disks around young intermediate-mass stars, a novel insight into planet formation challenges.

Findings

Accretion bursts destroy dust rings, impeding planetesimal formation.

Inner disk regions experience temperature increases that activate MRI.

Disks around intermediate-mass stars are less conducive to planet formation.

Abstract

We investigate the occurrence of accretion bursts, dust accumulation, and the prospects for planetesimal formation in a gravitationally unstable magnetized protoplanetary disk with globally suppressed but episodically triggered magnetorotational instability (MRI), particularly in young intermediate-mass stars (YIMSs) but with a brief comparison to low-mass counterparts. We use numerical magnetohydrodynamics simulations in the thin-disk limit (FEOSAD code) to model the formation and long-term evolution of a gravitationally unstable magnetized protoplanetary disk, including dust dynamics and growth, since the collapse of a massive slowly-rotating prestellar cloud core. Massive gas concentrations and dust rings form within the inner disk region owing to the radially varying efficiency of mass transport by gravitational instability (GI). These rings are initially susceptible to streaming instability (SI). However, gradual warming of the dust rings, thanks to high opacity and GI-induced influx of matter increases the gas temperature above a threshold for the MRI to develop via thermal ionization of alkaline metals. The ensuing MRI bursts destroy the dust rings, making planetesimal formation via SI problematic. In the later evolution phase, when the burst activity starts to diminish, SI becomes inefficient because of growing dust drift velocity and more extended inner dead zone, both acting to reduce the dust concentration below the threshold for SI to develop. Low-mass objects appear to be less affected by these adverse effects. Our results suggest that disks around young intermediate-mass stars may be challenging environments for planetesimal formation via SI. This may explain the dearth of planets around stars with $M_\ast > 3.0 \,$$M_\odot$.