Singular Isothermal Disks: II. Nonaxisymmetric Bifurcations and Equilibria

Abstract

We review the difficulties of the classical fission and fragmentation hypotheses for the formation of binary and multiple stars. A crucial missing ingredient in previous theoretical studies is the inclusion of dynamically important levels of magnetic fields. As a minimal model for a candidate presursor to the formation of binary and multiple stars, we therefore formulate and solve the problem of the equilibria of isopedically magnetized, singular isothermal disks, without the assumption of axial symmetry. Considerable analytical progress can be made if we restrict our attention to models that are scale-free, i.e., that have surface densities that vary inversely with distance from the rotation axis of the system. In agreement with earlier analysis by Syer and Tremaine, we find that lopsided (M=1) configurations exist at any dimensionless rotation rate, including zero. Multiple-lobed (M = 2, 3, 4, ...) configurations bifurcate from an underlying axisymmetric sequence at progressively higher dimensionless rates of rotation, but such nonaxisymmetric sequences always terminate in shockwaves before they have a chance to fission into M=2, 3, 4, ... separate bodies. On the basis of our experience in this paper, and the preceding Paper I, we advance the hypothesis that binary and multiple star-formation from smooth (i.e., not highly turbulent) starting states that are supercritical but in unstable mechanical balance requires the rapid (i.e., dynamical) loss of magnetic flux at some stage of the ensuing gravitational collapse.

arXiv comment49 pages, 11 figures, LaTeX, needs aaspp4.sty. The Astrophysical Journal, in press

References in corpus (6)

• First Observations of the Magnetic Field Geometry in Pre-stellar Cores
• Protostellar fragmentation in a power-law density distribution
• Consistency of Ambipolar Diffusion Models with Infall in the L1544 Protostellar Core
• A High Resolution Study of the Slowly Contracting, Starless Core L1544
• Non-axisymmetric, scale-free, razor-thin discs
• Axisymmetric Self-Similar Equilibria of Self-Gravitating Isothermal Systems

Cited by in corpus (27)

• Control of star formation by supersonic turbulence
• The Physics of Star Formation
• The stellar mass spectrum from non-isothermal gravoturbulent fragmentation
• Collapse of Magnetized Singular Isothermal Toroids: II. Rotation and Magnetic Braking
• The Formation of Stellar Clusters in Turbulent Molecular Clouds: Effects of the Equation of State
• Effects of the Equation of State on the Formation of Star Clusters
• The dust temperature distribution in prestellar cores
• A Turbulent Interstellar Medium Origin of the Binary Period Distribution
• The kinematics of lopsided galaxies
• Monte Carlo radiative transfer in molecular cloud cores
• Binary and Multiple Star Formation in Magnetic Clouds: Bar Growth and Fragmentation
• Fragmentation of Magnetically Subcritical Clouds into Multiple Supercritical Cores and the Formation of Small Stellar Groups
• Magnetohydrodynamic Density Waves in a Composite Disk System of Interstellar Medium and Cosmic-Ray Gas
• Axisymmetric stability criterion for two gravitationally coupled singular isothermal discs
• Stationary perturbation configurations in a composite system of stellar and coplanarly magnetized gaseous singular isothermal discs
• Nonaxisymmetric Evolution of Magnetically Subcritical Clouds: Bar Growth, Core Elongation, and Binary Formation
• Perturbation configurations in a two-fluid system of singular isothermal disks
• Stationary Nonaxisymmetric Configurations of Magnetized Singular Isothermal Disks
• On the existence of three-dimensional hydrostatic and magnetostatic equilibria of self-gravitating fluid bodies
• Self-Similar Equilibria of Self-Gravitating, Magnetized, Rotating, Isothermal Systems
• Relativistic Self-similar Disks
• Global Perturbation Configurations in a Composite Disc System with an Isopedic Magnetic Field
• Axisymmetric stability criteria for a composite system of stellar and magnetized gaseous singular isothermal discs
• Unstable modes of non-axisymmetric gaseous discs
• Scale-free equilibria of self-gravitating gaseous disks with flat rotation curves
• Nonaxisymmetric Neutral Modes in Relativistic Disks
• Cooling Flows of Self-Gravitating, Rotating, Viscous Systems