A numerical study of the effects of ambipolar diffusion on the collapse of magnetic gas clouds

Black, David C.; Scott, E. H.

doi:10.1086/160541

Cited by 36 publications

(18 citation statements)

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“…This mechanism was originated [57] to explain jets generated near black holes. This mechanism was originated [57] to explain jets generated near black holes.…”

Section: Winds and Outflowsmentioning

confidence: 99%

Principles of Star Formation

Bodenheimer

2011

Astronomy and Astrophysics Library

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“…This mechanism was originated [57] to explain jets generated near black holes. This mechanism was originated [57] to explain jets generated near black holes.…”

Section: Winds and Outflowsmentioning

confidence: 99%

Principles of Star Formation

Bodenheimer

2011

Astronomy and Astrophysics Library

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“…When the magnetic field becomes too weak, it is overwhelmed by self-gravity, and the cloud begins a dynamic contraction to form a star. The process of magnetic leakage during cloud contraction has been extensively investigated both analytically (e.g., Mestel & Spitzer 1956;Nakano & Tademaru 1972) and numerically (e.g., Nakano 1979;Black & Scott 1982;Lizano & Shu 1989;Ciolek & Mouschovias 1993;Basu & Mouschovias 1994;Li 1999;Mouschovias & Ciolek 1999). Specific models based on this scenario appear able to explain the observations of wellstudied dense cores B1 and L1544 (Crutcher et al 1994;Ciolek & Basu 2000;.…”

Section: Introductionmentioning

confidence: 99%

Binary and Multiple Star Formation in Magnetic Clouds: Bar Growth and Fragmentation

Nakamura

2003

ApJ

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In the standard scenario of isolated low-mass star formation, strongly magnetized molecular clouds are envisioned to condense gradually into dense cores, driven by ambipolar diffusion. Once the cores become magnetically supercritical, they collapse to form stars. Previous studies based on this scenario are limited to axisymmetric calculations leading to single supercritical core formation. The assumption of axisymmetry has precluded a detailed investigation of cloud fragmentation, generally thought to be a necessary step in the formation of binary and multiple stars. In a series of papers, we studied the nonaxisymmetric evolution of initially magnetically subcritical clouds, using a two-dimensional magnetohydrodynamic code based on the physically motivated thin-disk approximation. We found that such clouds become unstable to nonaxisymmetric perturbations after the supercritical cores are formed, because of ambipolar diffusion. In this paper, we focus on the evolution of clouds perturbed by an m ¼ 2 mode of a modest fractional amplitude of 5%, with an eye on binary and multiple star formation. We show that for a wide range of initial cloud parameters, the m ¼ 2 mode grows nonlinearly into a bar during the isothermal collapse after the supercritical core formation. The instability is driven by the domination of the magnetically diluted gravity over the combined thermal and magnetic pressure gradient in the supercritical cores. Such gravity-dominated cores can break up into fragments during or after the isothermal phase of cloud evolution. The outcome of fragmentation depends on the initial cloud conditions, such as the magnetic field strength, rotation rate, amount of cloud mass (relative to thermal Jeans mass), and mass distribution. It is classified into three different types: (1) '' separate-core formation,'' in which the bar (m ¼ 2) mode breaks up into two separate cores during the isothermal collapse, with a core separation of order 10 4 AU, (2) '' bar fragmentation,'' in which the m ¼ 2 mode evolves into a needle-like, opaque '' first bar '' (at a density ne10 12 cm À3 ), which breaks up into multiple fragments with initial masses of order 10 À2 M and separations of order 10 2 -10 3 AU, and (3) '' disk fragmentation,'' in which the bar growth remains slow during the isothermal collapse and the central region evolves into a rapidly rotating, opaque '' first disk,'' which breaks up into several self-gravitating blobs with separations less than the disk size (d10 2 AU). These three types of fragmentation loosely correspond to the empirical classification of embedded binary and multiple systems of Looney, Mundy, & Welch, based on millimeter dust continuum observations. The well-studied starless core L1544 appears to belong to the bar fragmentation type. We expect it to produce a highly elongated, opaque bar at the center in the future, which should break up into fragments of initial masses in the substellar regime.

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“…The role of the magnetic Ðeld is often simply characterized by a critical mass that M crit depends on the magnetic Ñux threading the cloud (Mestel & Spitzer 1956 ;Mouschovias & Spitzer 1976 ;Shu, Adams, & Lizano 1987 ;Tomisaka, Ikeuchi, & Nakamura 1988 ;McKee et al 1993 ;Mestel 1999). Clouds with M [ M crit are termed supercritical and collapse on a dynamical timescale : the magnetic Ðeld can have a moderate e †ect on the morphology of collapse and can slow collapse in the cloud envelope (e.g., Black & Scott 1982), but cannot signiÐcantly slow collapse in the core. Clouds with are termed M \ M crit subcritical and evolve on a longer timescale as magnetic support is lost as a result of ambipolar di †usion.…”

Section: Introductionmentioning

confidence: 99%

Fragmentation Instability of Molecular Clouds: Numerical Simulations

Indebetouw

Zweibel

2000

ApJ

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We simulate fragmentation and gravitational collapse of cold, magnetized molecular clouds. We explore the nonlinear development of an instability mediated by ambipolar di †usion, in which the collapse rate is intermediate to fast gravitational collapse and slow quasistatic collapse. Initially uniform stable clouds fragment into elongated clumps with masses largely determined by the cloud temperature, but substantially larger than the thermal Jeans mass. The clumps are asymmetric, with signiÐcant rotation and vorticity, and lose magnetic Ñux as they collapse. The clump shapes, intermediate collapse rates, and infall proÐles may help explain observations not easily Ðt by contemporary slow or rapid collapse models.

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A numerical study of the effects of ambipolar diffusion on the collapse of magnetic gas clouds

Cited by 36 publications

References 0 publications

Principles of Star Formation

Principles of Star Formation

Binary and Multiple Star Formation in Magnetic Clouds: Bar Growth and Fragmentation

Fragmentation Instability of Molecular Clouds: Numerical Simulations

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