Stability of Magnetized Disks and Implications for Planet Formation

Abstract

This paper considers gravitational perturbations in geometrically thin disks with rotation curves dominated by a central object, but with substantial contributions from magnetic pressure and tension. The treatment is general, but the application is to the circumstellar disks that arise during the gravitational collapse phase of star formation. We find the dispersion relation for spiral density waves in these generalized disks and derive the stability criterion for axisymmetric $(m=0)$ disturbances (the analog of the Toomre parameter $Q_T$) for any radial distribution of the mass-to-flux ratio $\lambda$. The magnetic effects work in two opposing directions: on one hand, magnetic tension and pressure stabilize the disk against gravitational collapse and fragmentation; on the other hand, they also lower the rotation rate making the disk more unstable. For disks around young stars the first effect generally dominates, so that magnetic fields allow disks to be stable for higher surface densities and larger total masses. These results indicate that magnetic fields act to suppress the formation of giant planets through gravitational instability. Finally, even if gravitational instability can form a secondary body, it must lose an enormous amount of magnetic flux in order to become a planet; this latter requirement represents an additional constraint for planet formation via gravitational instability and places a lower limit on the electrical resistivity.

accepted in ApJ

References in corpus (11)

• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• Optical Images of an Exosolar Planet 25 Light Years from Earth
• Gravitational collapse of magnetized clouds. I. Ideal MHD accretion flow
• Emergence of Protoplanetary Disks and Successive Formation of Gaseous Planets by Gravitational Instability
• Gravitational collapse of magnetized clouds II. The role of Ohmic dissipation
• Mean-Field Magnetohydrodynamics of Accretion Disks
• A Photoevaporating Rotating Disk in the Cepheus A HW2 Star Cluster
• Migration of Extrasolar Planets: Effects from X-Wind Accretion Disks
• Unveiling the main heating sources in the Cepheus A HW2 region
• The Challenge of Sub-Keplerian Rotation for Disk Winds
• Magnetic field regulated infall on the disc around the massive protostar Cepheus A HW2

Cited by in corpus (11)

• Collapse, outflows and fragmentation of massive, turbulent and magnetized prestellar barotropic cores
• Gas Giants in Hot Water: Inhibiting Giant Planet Formation and Planet Habitability in Dense Star Clusters Through Cosmic Time
• Rossby Wave Instability in Accretion Discs with Large-Scale Poloidal Magnetic Fields
• Migrating Planets into Ultra-Short-Period Orbits during Episodic Accretion Events
• Vertical Structure of Magnetized Accretion Disks around Young Stars
• Linear stability of magnetized massive protoplanetary disks
• Linear Stability Analysis of a Magnetic Rotating Disk with Ohmic Dissipation and Ambipolar Diffusion
• Magnetic Spirals in Accretion Flows Originated from Misaligned Magnetic Field
• Gravitational Collapse and Disk Formation in Magnetized Cores
• Inertial-Acoustic Oscillations of Black-Hole Accretion Discs with Large-Scale Poloidal Magnetic Fields
• Drag-driven instability of a dust layer in a magnetized protoplanetary disc