Thermal Instabilities in Interstellar Gas Heated by Cosmic Rays

Goldsmith, Donald

doi:10.1086/150511

Cited by 29 publications

(24 citation statements)

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“…1), the Field criterion is satisfied for primordial gas in this region for a fixed molecular fraction. Thermal instability can also be driven by a change in chemical composition, such as ionization/recombination (Defouew 1970;Goldsmith 1970) or molecule formation/dissociation (Yoneyama 1973). Sabano & Yoshii (1977) and Silk (1983) suggest that primordial gas can be chemo-thermally unstable.…”

Section: Thermal Instability and Fragmentationmentioning

confidence: 99%

Formation of Primordial Stars in a ΛCDM Universe

Yoshida

Omukai

Hernquist

et al. 2006

ApJ

494

732

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Primordial stars are formed from a chemically pristine gas consisting of hydrogen and helium. They are believed to have been born at some early epoch in the history of the Universe and to have enriched the interstellar medium with synthesized heavy elements before the emergence of ordinary stellar populations. We study the formation of the first generation of stars in the standard cold dark matter model. We follow the gravitational collapse and thermal evolution of primordial gas clouds within early cosmic structures using very high-resolution, cosmological hydrodynamic simulations. Our simulation achieves a dynamic range of ∼ 10 10 in length scale. With accurate treatment of atomic and molecular physics, it allows us to study the chemo-thermal evolution of primordial gas clouds to densities up to ρ ∼ 2 × 10 −8 g cm −3 (n H ∼ 10 16 cm −3 ) without assuming any a priori equation of state; a six orders of magnitudes improvement over previous three-dimensional calculations. We implement an extensive chemistry network for hydrogen, helium and deuterium. All the relevant atomic and molecular cooling and heating processes, including cooling by collision-induced continuum emission, are implemented. For calculating optically thick H 2 cooling at high densities, we use the Sobolev method (Sobolev 1960) and evaluate the molecular line opacities for a few hundred lines. We validate the accuracy of the method by performing a spherical collapse test and comparing the results with those of accurate one-dimensional calculations that treat the line radiative transfer problem in a fully self-consistent manner.We then perform a cosmological simulation adopting the standard ΛCDM model. Dense gas clumps are formed at the centers of low mass (∼ 10 5−6 M ⊙ ) dark matter halos at redshifts z ∼ 20, and they collapse gravitationally when the cloud mass exceeds a few hundred solar masses. To examine possible gas fragmentation owing to thermal instability, we compute explicitly the growth rate of isobaric perturbations. We show that the cloud core does not fragment in either the low-density (n H ∼ 10 10 cm −3 ) or high-density (∼ 10 15 cm −3 ) regimes, where gas cooling rate is increased owing to three-body molecule formation and collision-induced emission, respectively. The cloud core becomes marginally unstable against chemo-thermal instability in the low-density regime. However, since the core is already compact at that point and correspondingly the sound-crossing time as well as the free-fall time are short, or comparable to the perturbation growth timescale, it does not fragment. Run-away cooling simply leads to fast condensation of the core to form a single proto-stellar seed. We also show that the core remains stable against gravitational deformation and fragmentation throughout the evolution. We trace in Lagrangian space the gas elements that end up at the center of the cloud, and study the evolution of the specific angular momentum. We show that, during the final dynamical collapse, small angular momentum material collapses faster...

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Section: Thermal Instability and Fragmentationmentioning

confidence: 99%

Formation of Primordial Stars in a ΛCDM Universe

Yoshida

Omukai

Hernquist

et al. 2006

ApJ

494

732

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“…Goldsmith (1970) and Schwarz, McCray, & Stein (1972) first computed the nonlinear development of the thermal instability, demonstrating that shock waves form during the dynamical collapse of nonlinear regions. Hennebelle & Pérault (1999) demonstrated that shock compression can trigger thermal instability in otherwise stable regions in the diffuse ISM, even in the presence of magnetic fields (Hennebelle & Pérault 2000), so that compressions much greater than the isothermal factor of M 2 can occur (see the quantitative discussion by Vázquez-Semadeni et al 1996).…”

Section: A Formation and Lifetime Of Molecular Cloudsmentioning

confidence: 99%

Control of star formation by supersonic turbulence

2004

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Understanding the formation of stars in galaxies is central to much of modern astrophysics. However, a quantitative prediction of the star formation rate and the initial distribution of stellar masses remains elusive. For several decades it has been thought that the star formation process is primarily controlled by the interplay between gravity and magnetostatic support, modulated by neutral-ion drift (known as ambipolar diffusion in astrophysics). Recently, however, both observational and numerical work has begun to suggest that supersonic turbulent flows rather than static magnetic fields control star formation. To some extent, this represents a return to ideas popular before the importance of magnetic fields to the interstellar gas was fully appreciated. This review gives a historical overview of the successes and problems of both the classical dynamical theory, and the standard theory of magnetostatic support from both observational and theoretical perspectives. The outline of a new theory relying on control by driven supersonic turbulence is then presented. Numerical models demonstrate that although supersonic turbulence can provide global support, it nevertheless produces density enhancements that allow local collapse. Inefficient, isolated star formation is a hallmark of turbulent support, while efficient, clustered star formation occurs in its absence. The consequences of this theory are then explored for both local star formation and galactic scale star formation. It suggests that individual star-forming cores are likely not quasi-static objects, but dynamically collapsing. Accretion onto these objects varies depending on the properties of the surrounding turbulent flow; numerical models agree with observations showing decreasing rates. The initial mass distribution of stars may also be determined by the turbulent flow. Molecular clouds appear to be transient objects forming and dissolving in the larger-scale turbulent flow, or else quickly collapsing into regions of violent star formation. We suggest that global star formation in galaxies is controlled by the same balance between gravity and turbulence as small-scale star formation, although modulated by cooling and differential rotation. The dominant driving mechanism in star-forming regions of galaxies appears to be supernovae, while elsewhere coupling of rotation to the gas through magnetic fields or gravity may be important.

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“…In astrophysics, a flow involving magnetised gas is typically ionized, compressible, and often supersonic. Since the interstellar gas has essentially infinite conductivity [1], we treat the flow by solving the ideal magnetohydrodynamics (MHD) equations. From the hyperbolic nature of the ideal MHD equations, it is known that discontinuous solutions may develop even from smooth initial data.…”

Section: Introductionmentioning

confidence: 99%

A novel high-order, entropy stable, 3D AMR MHD solver with guaranteed positive pressure

Derigs

Winters

Gassner

et al. 2016

Journal of Computational Physics

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We describe a high-order numerical magnetohydrodynamics (MHD) solver built upon a novel non-linear entropy stable numerical flux function that supports eight travelling wave solutions. By construction the solver conserves mass, momentum, and energy and is entropy stable. The method is designed to treat the divergence-free constraint on the magnetic field in a similar fashion to a hyperbolic divergence cleaning technique. The solver described herein is especially well-suited for flows involving strong discontinuities. Furthermore, we present a new formulation to guarantee positivity of the pressure. We present the underlying theory and implementation of the new solver into the multi-physics, multi-scale adaptive mesh refinement (AMR) simulation code FLASH (http://flash.uchicago.edu). The accuracy, robustness and computational efficiency is demonstrated with a number of tests, including comparisons to available MHD implementations in FLASH.

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Thermal Instabilities in Interstellar Gas Heated by Cosmic Rays

Cited by 29 publications

References 0 publications

Formation of Primordial Stars in a ΛCDM Universe

Formation of Primordial Stars in a ΛCDM Universe

Control of star formation by supersonic turbulence

A novel high-order, entropy stable, 3D AMR MHD solver with guaranteed positive pressure

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