Gravitational Collapse in Turbulent Molecular Clouds. II. Magnetohydrodynamical Turbulence

By F. Heitsch, M. Mac Low, Ralf Klessen. 2000

170 citations recorded by the source corpus.

Hydrodynamic supersonic turbulence can only prevent local gravitational collapse if the turbulence is driven on scales smaller than the local Jeans lengths in the densest regions, which is a very severe requirement (see Paper I). Magnetic fields have been suggested to support molecular clouds either magnetostatically or via magnetohydrodynamic (MHD) waves. Whereas the first mechanism would form sheetlike clouds, the second mechanism not only could exert a pressure onto the gas counteracting the gravitational forces but could lead to a transfer of turbulent kinetic energy down to smaller spatial scales via MHD wave interactions. This turbulent magnetic cascade might provide sufficient energy at small scales to halt local collapse. We test this hypothesis with MHD simulations at resolutions up to 2563 zones done with ZEUS-3D. We first derive a resolution criterion for self-gravitating, magnetized gas: to prevent collapse of magnetostatically supported regions caused by numerical diffusion, the minimum Jeans length must be resolved by four zones. Resolution of MHD waves increases this requirement to roughly six zones. We then find that magnetic fields cannot prevent local collapse unless they provide magnetostatic support. Weaker magnetic fields do somewhat delay collapse and cause it to occur more uniformly across the supported region in comparison to the hydrodynamical case. However, they still cannot prevent local collapse for much longer than a global free-fall time.

Subfields: Astronomy and Astrophysics, Atmospheric Science

View Paper: https://www.semanticscholar.org/paper/e4b6684e86175aab001db913c71569ba737923a2

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Citations in the corpus

Protostellar Turbulence Driven by Collimated Outflows (2007, background): “…stage of gravitational evolution distinguishes our simulations from other grid-based simulations of cluster formation in turbulent clouds (e.g., Heitsch et al. 2001; Ostriker et al. 2001; Li et al. 2004; Tilley & Pudritz 2004; Vazquez-Semadeni et al. 2005; for examples of SPH simulation of…”
Physical Processes in the Interstellar Medium (2014, background): “However, converting polarization into magnetic field strength is very difficult (Heitsch et al., 2001b).”
LIMITING ACCRETION ONTO MASSIVE STARS BY FRAGMENTATION-INDUCED STARVATION (2010, background): “This objection is, however, weakened by the fact that magnetic fields are able to reduce the level of fragmentation on scales of molecular clouds as a whole (Heitsch et al. 2001) as well as of collapsing cloud cores (Hennebelle & Fromang 2008; Hennebelle & Teyssier 2008).”
Astrophysical smooth particle hydrodynamics (2009, background): “Successful implementations of such individual time step schemes can be found, for example, in [187,188,3,123,189,12,190,151].”
Interstellar Turbulence I: Observations and Processes (2004, background): “What magnetic fields appear to do is reduce the core density contrast (Balsara, Crutcher & Pouquet 2001) and slow down the local collapse rate (Heitsch et al. 2001).”
The physics of star formation (2003, background): “Magnetic forces will then remain less important than gravity throughout the collapse, serving mainly to retard the collapse somewhat compared to the non-magnetic case (Indebetouw and Zweibel 2000; Heitsch et al 2001).”
THE STAR FORMATION RATE OF TURBULENT MAGNETIZED CLOUDS: COMPARING THEORY, SIMULATIONS, AND OBSERVATIONS (2012, background): “…we evolve the MHD equations for two turbulent crossing times, 2T = L/(Mcs) without self-gravity, in order to establish fully developed, compressible turbulence (e.g., Klessen et al. 2000; Klessen 2001; Heitsch et al. 2001; Federrath et al. 2009, 2010b; Price & Federrath 2010; Micic et al. 2012).”
The Density Probability Distribution in Compressible Isothermal Turbulence: Solenoidal versus Compressive Forcing (2008, background): “…turbulence with solenoidal or weakly compressive forcing (e.g., Stone et al. 1998; Mac Low et al. 1998; Mac Low 1999; Klessen et al. 2000; Heitsch et al. 2001; Boldyrev et al. 2002; Li et al. 2003; Padoan et al. 2004; Jappsen et al. 2005; Ballesteros-Paredes et al. 2006; Kritsuk et al.…”
Accretion-driven turbulence as universal process: galaxies, molecular clouds, and protostellar disks (2009, methodology): “The power spectrum of v has been calculated in several studies (e.g. Klessen et al. 2000; Heitsch et al. 2001; Kritsuk et al. 2007; Federrath et al. 2009) and typically been found to be P(v) ∝ k−1.9.”
MODELING COLLAPSE AND ACCRETION IN TURBULENT GAS CLOUDS: IMPLEMENTATION AND COMPARISON OF SINK PARTICLES IN AMR AND SPH (2010, background): “For mhd calculations, Heitsch et al. (2001) find that more than four cells are required.”
Comparing the statistics of interstellar turbulence in simulations and observations - Solenoidal versus compressive turbulence forcing (2009, methodology): “The effects of varying the scale of energy input were investigated by Mac Low (1999), Klessen et al. (2000), Heitsch et al. (2001) and Vázquez-Semadeni et al. (2003).”
THE FRACTAL DENSITY STRUCTURE IN SUPERSONIC ISOTHERMAL TURBULENCE: SOLENOIDAL VERSUS COMPRESSIVE ENERGY INJECTION (2007, methodology): “…studies (e.g., Padoan et al. 1997; Passot & Vázquez-Semadeni 1998; Stone et al. 1998; Mac Low et al. 1998; Mac Low 1999; Klessen et al. 2000; Heitsch et al. 2001; Boldyrev et al. 2002; Li et al. 2003; Padoan et al. 2004b; Jappsen et al. 2005; Ballesteros-Paredes et al. 2006; Kritsuk et al.…”
FORMATION OF MASSIVE MOLECULAR CLOUD CORES BY CLOUD–CLOUD COLLISION (2013, result): “This result is consistent with the Heitsch et al. (2001) and Federrath et al. (2010), which showed that tens of numerical cells are necessary to resolve turbulent eddies.”