On the origin of magnetic fields in stars

Abstract

Are the kG-strength magnetic fields observed in young stars a fossil field left over from their formation or are they generated by a dynamo? We use radiation non-ideal magnetohydrodynamics simulations of the gravitational collapse of a rotating, magnetized molecular cloud core over 17 orders of magnitude in density, past the first hydrostatic core to the formation of the second, stellar core, to examine the fossil field hypothesis. Whereas in previous work we found that magnetic fields in excess of 10 kG can be implanted in stars at birth, this assumed ideal magnetohydrodynamics (MHD), i.e. that the gas is coupled to the magnetic field. Here we present non-ideal MHD calculations which include Ohmic resistivity, ambipolar diffusion and the Hall effect. For realistic cosmic ray ionization rates, we find that magnetic field strengths of $\lesssim$ kG are implanted in the stellar core at birth, ruling out a strong fossil field. While these results remain sensitive to resolution, they cautiously provide evidence against a fossil field origin for stellar magnetic fields, suggesting instead that magnetic fields in stars originate in a dynamo process.

8 pages, 8 figures. Accepted for publication in MNRAS

References in corpus (21)

• SPLASH: An interactive visualisation tool for Smoothed Particle Hydrodynamics simulations
• Smoothed Particle Hydrodynamics and Magnetohydrodynamics
• Stellar magnetism: empirical trends with age and rotation
• The Magnetic Fields of Classical T Tauri Stars
• Magnetic fields in protoplanetary disks
• Hall magnetohydrodynamics of partially ionized plasmas
• Radiation Magnetohydrodynamic Simulations of Protostellar Collapse: Non-Ideal Magnetohydrodynamic Effects and Early Formation of Circumstellar Disks
• Effects of Ohmic and ambipolar diffusion on the formation and evolution of the first cores, protostars and circumstellar discs
• Constrained Hyperbolic Divergence Cleaning for Smoothed Particle Magnetohydrodynamics
• Protostellar birth with ambipolar and ohmic diffusion
• The impact of the Hall effect during cloud core collapse:implications for circumstellar disk evolution
• T Tauri stellar magnetic fields: He I measurements
• The collapse of a molecular cloud core to stellar densities using radiation non-ideal magnetohydrodynamics
• Constrained hyperbolic divergence cleaning in smoothed particle magnetohydrodynamics with variable cleaning speeds
• Ambipolar diffusion in smoothed particle magnetohydrodynamics
• NICIL: A stand alone library to self-consistently calculate non-ideal magnetohydrodynamic coefficients in molecular cloud cores
• The impact of non-ideal magnetohydrodynamics on binary star formation
• Spectropolarimetry of the Classical T Tauri Star TW Hydrae
• Hall effect-driven formation of gravitationally unstable discs in magnetized molecular cloud cores
• The effect of extreme ionisation rates during the initial collapse of a molecular cloud core
• Investigating prescriptions for artificial resistivity in smoothed particle magnetohydrodynamics

Cited by in corpus (22)

• The role of magnetic fields in the formation of protostellar discs
• There is no magnetic braking catastrophe: Low-mass star cluster and protostellar disc formation with non-ideal magnetohydrodynamics
• Disc formation and fragmentation using radiative non-ideal magnetohydrodynamics
• Origin of Misalignments: Protostellar Jet, Outflow, Circumstellar Disc, and Magnetic Field
• Non-ideal magnetohydrodynamics vs turbulence I: Which is the dominant process in protostellar disc formation?
• The impact of non-ideal magnetohydrodynamic processes on discs, outflows, counter-rotation and magnetic walls during the early stages of star formation
• Birth of convective low-mass to high-mass second Larson cores
• The Mean Magnetic Field Strength of CI Tau
• Non-ideal magnetohydrodynamics vs turbulence II: Which is the dominant process in stellar core formation?
• Do we need non-ideal magnetohydrodynamics to model protostellar discs?
• The birth and early evolution of a low mass protostar
• On the origin of magnetic fields in stars II: The effect of numerical resolution
• Different Modes of Star Formation II: Gas Accretion Phase of Initially Subcritical Star-Forming Clouds
• Ambipolar diffusion and the molecular abundances in prestellar cores
• Formation of low mass protostars and their circumstellar disks
• Birth of magnetized low-mass protostars and circumstellar disks
• Cosmic-ray ionization rate versus Dust fraction: Which plays a crucial role in the early evolution of the circumstellar disk?
• Jet formation in post-AGB binaries: Confronting cold magnetohydrodynamic disc wind wind models with observations
• Star-forming environments in smoothed particle magnetohydrodynamics simulations I: Clump extraction and properties
• Numerical Insights into Disk Accretion, Eccentricity, and Kinematics in the Class 0 phase
• Resolving numerical star formation: A cautionary tale
• Discovery and analysis of three magnetic hot subdwarf stars: evidence for merger-induced magnetic fields