Criteria for collapse and fragmentation of rotating, isothermal clouds

Miyama, S.; Hayashi, Chûshirô; Narita, Shinji

doi:10.1086/161926

Cited by 110 publications

(65 citation statements)

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“…Although the initial clouds have different radii and masses with different metallicities, the ratio of thermal to gravitational energy (α0), which significantly affects the cloud collapse (e.g. Miyama et al 1984;Tsuribe & Inutsuka 1999a,b), is the same for all models (α0 = 0.47).…”

Section: Initial Conditionsmentioning

confidence: 99%

Evolution of magnetic fields in collapsing star-forming clouds under different environments

Higuchi

Machida

Susa

2018

Monthly Notices of the Royal Astronomical Society

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In nearby star-forming clouds, amplification and dissipation of the magnetic field are known to play crucial roles in the star-formation process. The star-forming environment varies from place to place and era to era in galaxies. In the present study, amplification and dissipation of magnetic fields in star-forming clouds are investigated under different environments using magnetohydrodynamics (MHD) simulations. We consider various star-forming environments in combination with the metallicity and the ionization strength, and prepare prestellar clouds having two different mass-to-flux ratios. We calculate the cloud collapse until protostar formation using ideal and nonideal (inclusion and exclusion of Ohmic dissipation and ambipolar diffusion) MHD calculations to investigate the evolution of the magnetic field. We perform 288 runs in total and show the diversity of the density range within which the magnetic field effectively dissipates, depending on the environment. In addition, the dominant dissipation process (Ohmic dissipation or ambipolar diffusion) is shown to strongly depend on the star-forming environment. Especially, for the primordial case, magnetic field rarely dissipates without ionization source, while it efficiently dissipates when very weak ionization sources exist in the surrounding environment. The results of the present study help to clarify star formation in various environments.

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Section: Initial Conditionsmentioning

confidence: 99%

Evolution of magnetic fields in collapsing star-forming clouds under different environments

Higuchi

Machida

Susa

2018

Monthly Notices of the Royal Astronomical Society

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“…A remarkable amount of agreement is evident about the three possible endstates for collapse. Uniform density, isothermal clouds can expand to form equilibrium Bonnor-Ebert ellipsoids, collapse to form single protostars, or collapse and undergo fragmentation into two or more objects, depending on the initial values Of Cli = Ethermal/lEgravity] and ft = -Erototionaz/I^flrot^yl for t h e c l°u d -T h e empirical criteria (Figure 1) of Miyama et al (1984) are fairly good at delineating these three outcomes, with the exception of the low ft regime. Note the 'single' result for the a* = 0.55, ft = 0.02 model (Bodenheimer et al 1980), a model which clearly meets the o^ft < 0.12 criterion for fragmentation.…”

Section: Initially Uniform Density Cloudsmentioning

confidence: 99%

“…Because of the intrinsically nonlinear, three-dimensional, non-stationary nature of the fragmentation process, our analytical understanding is still very rudimentary, being limited either to simple arguments such as the Jeans mass or to empirically-derived relations (e.g., the o^ft < 0.12 constraint of Miyama et al 1984; see section 2). Essentially all of our knowledge of fragmentation has come from numerical hydrodynamics calculations.…”

Section: Introductionmentioning

confidence: 99%

The Fragmentation Mechanism

Boss

1992

International Astronomical Union Colloquium

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A B S T R A C T :Binary and multiple star systems may form by fragmentation, that is, through break-up of a dense molecular cloud core during the dynamical collapse phase that leads to the formation of protostellar objects. This review concentrates on theoretical models of fragmentation based on numerical hydrodynamical calculations in three spatial dimensions, using both finite-difference and smoothed particle hydrodynamics techniques. A variety of recent results are described, including calculations of the fragmentation of bar-like (prolate) clouds, fragmentation in clouds with initial power-law density and angular velocity distributions, tidally-induced fragmentation, fragmentation in cooling clouds, formation of hierarchical systems, and the dividing line between clouds that fragment and those that appear to form single protostars. A brief comparison of the predicted physical and dynamical properties of the theoretical fragments with the observed properties of main-sequence and pre-main-sequence binary stars lends supports to the hypothesis that fragmentation is the dominant formation mechanism for binary and multiple star systems. The major uncertainties regarding fragmentation are the extent to which precollapse clouds are susceptible to fragmentation, and the degree to which binary fragments undergo orbital decay and possibly mergers through interactions with the enveloping disk.

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“…A criterion for fragmentation in the presence of rotation was provided by the semi-analytical work of Tohline (1981), quantifying thermal support with the virial parameter α and the rotational versus gravitational energy in the cloud with the corresponding parameter β. The quantity αβ has since been used repeatedly to delimit the conditions for fragmentation (Miyama et al 1984, Hachisu & Eriguchi 1984, Tsuribe & Inutsuka 1999, Tohline 2002, for instance), and it was found that αβ < 0.1−0.2 typically leads to fragmentation.…”

Section: Introductionmentioning

confidence: 99%

Shell instability of a collapsing dense core

Ntormousi

Hennebelle

2015

A&A

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Aims. Understanding the formation of binary and multiple stellar systems largely comes down to studying the circumstances under which a condensing core fragments (or not) during the first stages of the collapse. However, both the probability of fragmentation and the number of fragments seem to be determined to a large degree by the initial conditions. In this work we explore this dependence by studying the fate of the linear perturbations of a homogeneous gas sphere, both analytically and numerically. Methods. In particular, we investigate the stability of the well-known homologous solution that describes the collapse of a uniform spherical cloud. One problem that arises in such treatments is the mathematical singularity in the perturbation equations, which corresponds to the location of the sonic point of the flow. This difficulty is surpassed here by explicitly introducing a weak shock next to the sonic point as a natural way of connecting the subsonic to the supersonic regimes. In parallel, we perform adaptive mesh refinement (AMR) numerical simulations of the linear stages of the collapse and compare the growth rates obtained by each method. Results. With this combination of analytical and numerical tools, we explore the behavior of both axisymmetric and non-axisymmetric perturbations. The numerical experiments provide the linear growth rates as a function of the core's initial virial parameter and as a function of the azimuthal wave number of the perturbation. The overlapping regime of the numerical experiments and the analytical predictions is the situation of a cold and large cloud, and in this regime the analytically calculated growth rates agree very well with the ones obtained from the simulations. Conclusions. The use of a weak shock as part of the perturbation allows us to find physically acceptable solutions to the equations for a continuous range of growth rates. The numerical simulations agree very well with the analytical prediction for the most unstable cores, while they impose a limit of a virial parameter of 0.1 for core fragmentation in the absence of rotation.

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Criteria for collapse and fragmentation of rotating, isothermal clouds

Cited by 110 publications

References 0 publications

Evolution of magnetic fields in collapsing star-forming clouds under different environments

Evolution of magnetic fields in collapsing star-forming clouds under different environments

The Fragmentation Mechanism

Shell instability of a collapsing dense core

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