The Athena++ Adaptive Mesh Refinement Framework: Multigrid Solvers for Self-gravity

Tomida, Kengo; Stone, James M.

doi:10.3847/1538-4365/acc2c0

Cited by 9 publications

(3 citation statements)

References 49 publications

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“…The total pressure P is composed of P = p + B 2 /2, where p is the gas thermal pressure. The gravitational potential f is obtained from the Poisson's equation, using the full multigrid method, implemented by Tomida & Stone (2023) with the multipole boundary condition,…”

Section: Methodsmentioning

confidence: 99%

Amplification and Saturation of Turbulent Magnetic Fields in Collapsing Primordial Gas Clouds

Higashi,

Susa,

Federrath

et al. 2024

ApJ

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Recent numerical studies suggest that magnetic fields play an important role in primordial star formation in the early Universe. However, the detailed evolution of the magnetic field in the collapse phase still has uncertainties because of the complicated physics associated with turbulence in a collapsing magnetized system. Here, we perform a suite of numerical MHD simulations that follow the collapse of magnetized, turbulent primordial gas clouds to investigate the evolution of the magnetic field associated with the turbulence, assuming a polytropic equation of state with exponent γ eff and with various numerical resolutions. In addition, we generalize the analytic theory of magnetic field growth/saturation so that it can deal with various exponents γ eff and turbulence energy spectra. We find that the numerical results are well reproduced by the theory for various γ eff through the collapse phase during the formation of the first stars. The magnetic field is eventually amplified by a factor of 1012–1015 due to kinematic and nonlinear turbulent dynamo effects and reaches 3%–100% of the equipartition level, depending on γ eff. We also find that the transition between the kinematic and nonlinear stages can be analytically estimated. These results indicate that the strong magnetic field accompanied by supersonic turbulence is a general property and suggest that it can play a crucial role in the formation of the first stars.

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Section: Methodsmentioning

confidence: 99%

Amplification and Saturation of Turbulent Magnetic Fields in Collapsing Primordial Gas Clouds

Higashi,

Susa,

Federrath

et al. 2024

ApJ

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“…We use the publicly available MHD simulation code Athena ++ (Stone et al 2020) to solve the basic equations, where we employ the HLLD MHD Riemann solver (Miyoshi & Kusano 2005) and the constrained transport method to integrate the magnetic fields (Evans & Hawley 1988;Gardiner & Stone 2005. The self-gravity is calculated with the full multigrid method (Tomida et al 2023).…”

Section: ( ) T Zmentioning

confidence: 99%

Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages

Kobayashi,

Iwasaki,

Tomida

et al. 2023

ApJ

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The formation of molecular clouds out of H i gas is the first step toward star formation. Its metallicity dependence plays a key role in determining star formation throughout cosmic history. Previous theoretical studies with detailed chemical networks calculate thermal equilibrium states and/or thermal evolution under one-zone collapsing background. The molecular cloud formation in reality, however, involves supersonic flows, and thus resolving the cloud internal turbulence/density structure in three dimensions is still essential. We here perform magnetohydrodynamics simulations of 20 km s−1 converging flows of warm neutral medium (WNM) with 1 μG mean magnetic field in the metallicity range from the solar (1.0 Z ⊙) to 0.2 Z ⊙ environment. The cold neutral medium (CNM) clumps form faster with higher metallicity due to more efficient cooling. Meanwhile, their mass functions commonly follow dn / dm ∝ m − 1.7 at three cooling times regardless of the metallicity. Their total turbulence power also commonly shows the Kolmogorov spectrum with its 80% in the solenoidal mode, while the CNM volume alone indicates the transition toward Larson’s law. These similarities measured at the same time in units of the cooling time suggest that the molecular cloud formation directly from the WNM alone requires a longer physical time in a lower-metallicity environment in the 1.0–0.2 Z ⊙ range. To explain the rapid formation of molecular clouds and subsequent massive star formation possibly within ≲10 Myr as observed in the Large/Small Magellanic Clouds, the H i gas already contains CNM volume instead of pure WNM.

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“…The constrained transport method was applied for maintaining the initial ∇ • B = 0 condition (Evans & Hawley 1988;Gardiner & Stone 2008). The multigrid algorithm was used to solve Poisson's equation (Equation ( 9)) and was implemented in Athena++ by Tomida & Stone (2023).…”

Section: Basic Equations Of Ideal Mhdmentioning

confidence: 99%

Simulation of Head-on Collisions between Filamentary Molecular Clouds Threaded by a Lateral Magnetic Field and Subsequent Evolution

Kashiwagi,

Iwasaki,

Tomisaka

2023

ApJ

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Filamentary molecular clouds are regarded as the place where newborn stars form. In particular, a hub region, a place where it appears as if several filaments are colliding, often indicates active star formation. To understand the star formation in filament structures, we investigate the collisions between two filaments using two-dimensional magnetohydrodynamical simulations. As a model of filaments, we assume that the filaments are in magnetohydrostatic equilibrium under a global magnetic field perpendicular to the filament axis. We set two identical filaments with an infinite length and make them collide with a zero-impact parameter (head-on). When the two filaments collide while sharing the same magnetic flux, we found two types of evolution after a merged filament is formed: runaway radial collapse and stable oscillation with a finite amplitude. The condition for the radial collapse is independent of the collision velocity and is given by the total line mass of the two filaments exceeding the magnetically critical line mass for which no magnetohydrostatic solution exists. The radial collapse proceeds in a self-similar manner, resulting in a unique distribution irrespective of the various initial line masses of the filament, as the collapse progresses. When the total line mass is less massive than the magnetically critical line mass, the merged filament oscillates, and the density distribution is well-fitted by a magnetohydrostatic equilibrium solution. The condition necessary for the radial collapse is also applicable to the collision whose direction is perpendicular to the global magnetic field.

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The Athena++ Adaptive Mesh Refinement Framework: Multigrid Solvers for Self-gravity

Cited by 9 publications

References 49 publications

Amplification and Saturation of Turbulent Magnetic Fields in Collapsing Primordial Gas Clouds

Amplification and Saturation of Turbulent Magnetic Fields in Collapsing Primordial Gas Clouds

Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages

Simulation of Head-on Collisions between Filamentary Molecular Clouds Threaded by a Lateral Magnetic Field and Subsequent Evolution

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