YSO Jets Magnetocentrifugally Driven by Reconnecting Atmospheric Avalanche Accretion Streams Above Inner Circumstellar Disks

TL;DR

This paper uses 2D MHD simulations to demonstrate that magnetocentrifugal forces driven by reconnecting avalanche accretion streams above inner circumstellar disks can produce fast, collimated jets in young stellar objects, linking magnetic reconnection to jet launching.

Contribution

It introduces a novel mechanism where reconnecting avalanche accretion streams drive jets, expanding understanding of YSO jet origins beyond traditional models.

Findings

Fast bipolar jets (>100 km/s) are driven by magneto-centrifugal forces.

Reconnection of poloidal magnetic fields heats plasma, potentially forming chondrules and CAIs.

Jets are sustained by gravitational energy release from avalanche accretion streams.

Abstract

Fast, collimated jets are ubiquitous features of young stellar objects (YSOs). They are generally thought to be powered by disk accretion, but the details are debated. Through 2D (axisymmetric) MHD simulations, we find that a fast ($>100$~km/s) collimated bipolar jet is continuously driven along the north and south poles of the circumstellar disk that is initially magnetized by a large-scale open poloidal field and contains a thermally ionized inner magnetically active zone surrounded by a dead zone. The fast jet is primarily driven magneto-centrifugally by the release of the gravitational binding energy of the so-called ``avalanche accretion streams" near the boundary of an evacuated poloidal field-dominated polar region and a thick disk atmosphere raised by a toroidal magnetic field. Specifically, the fast outflow is driven along the upper (open) branch of the highly pinched poloidal field lines threading the (strongly magnetically braked) accretion streams where the density is relatively low so that the lightly loaded material can be accelerated magneto-centrifugally along the open field line to a high speed. The highly pinched poloidal magnetic fields threading the avalanche accretion streams tend to reconnect, enabling mass to accrete to the center without dragging along the poloidal magnetic flux with it. The reconnection provides a potential heating source for producing chondrules and calcium- and aluminum-rich inclusions (CAIs).