Accretion Disk Magnetic Braking

TL;DR

This paper derives analytical equations describing how magnetic fields brake protostellar disks, influencing accretion rates and disk evolution, providing insights and tools for modeling star formation.

Contribution

It introduces new analytical equations for disk accretion speed, mass accretion rate, and related properties under magnetic braking in protostellar disks.

Findings

Analytic expressions for accretion speed and rate.

Equations for disk energy dissipation and evolution.

Potential applications for validating computational models.

Abstract

A protostellar disk is threaded by a static magnetic field that is perpendicular to the disk-surface. The magnetic field acts to brake the protostellar disk and cause the disk material to move towards the protostar. General analytic equations are derived for the accretion speed, and mass accretion rate. Simplified analytic equations are also obtained for the disk energy dissipation, accretion timescale and the disk radial position plus disk surface density, as a function of time. In addition to providing physical insight, such equations might be useful as a check on computational models for protostar and protostellar disk formation.