The Turbulent Dynamo in Highly Compressible Supersonic Plasmas

Federrath, Christoph; Schober, Jennifer; Bovino, S.; Schleicher, Dominik R. G.

doi:10.1088/2041-8205/797/2/l19

Cited by 123 publications

(151 citation statements)

References 50 publications

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“…We seed the simulations with trace initial magnetic fields; these fields are amplified by the turbulent dynamo until they saturate around equipartition (magnetic energy about ∼5% of the kinetic energy, in good agreement with other simulations using a variety of different numerical techniques and analytic estimates; see Schekochihin et al 2004;Brandenburg & Subramanian 2005;Federrath et al 2014). However,because they only indirectly influence the dynamics by weakly changing the structure of turbulence, we find that magnetic fields do not significantly change our conclusions compared to hydro-only runs.…”

Section: A3 Initial Conditionssupporting

confidence: 77%

Are the Formation and Abundances of Metal-poor Stars the Result of Dust Dynamics?

Hopkins

Conroy

2017

ApJ

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Large dust grains can fluctuate dramatically in their local density, relative to the gas, in neutralturbulent disks. Small, high-redshift galaxies (before reionization) represent ideal environments for this process. We show via simple arguments and simulations that order-of-magnitude fluctuations are expected in local abundances of large grains (>100 Å) under these conditions. This can have important consequences for star formation and stellar metal abundances in extremely metal-poor stars. Low-mass stars canform in dust-enhanced regions almost immediately after some dust formseven if the galaxy-average metallicity is too low for fragmentation to occur. We argue that the metal abundances of these "promoted" stars may contain interesting signaturesas the CNO abundances (concentrated in large carbonaceous grains and ices) and Mg and Si (in large silicate grains) can be enhanced and/or fluctuate almost independently. Remarkably, the otherwise puzzling abundance patterns of some metal-poor stars can be wellfit by standardIMF-averaged core-collapse SNe yieldsif we allow for fluctuating local dust-to-gas ratios. We also show that the observed log-normaldistribution of enhancements in these species agrees with our simulations. Moreover, we confirm that Mg and Si are correlated in these stars;theabundance ratios are similar to those in local silicate grains. Meanwhile [Mg/Ca], predicted to be nearly invariant from pure SNe yields, shows very large enhancements and variations up to factors of 100 as expected in the dust-promoted model, preferentially in the [C/Fe]-enhanced metal-poor stars. Together, this suggests that (1) dust exists in second-generation star formation, (2) local dust-to-gas ratio fluctuations occur inprotogalaxies and can be important for star formation, and (3) the light element abundances of these stars may be affected by the local chemistry of dust where they formed, rather than directly tracing nucleosynthesis from earlier populations.

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Section: A3 Initial Conditionssupporting

confidence: 77%

Are the Formation and Abundances of Metal-poor Stars the Result of Dust Dynamics?

Hopkins

Conroy

2017

ApJ

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“…This corresponds to the exponential growth phase, and is characteristic for the small-scale dynamo [37; 44]. The power spectra converge first on the smallest spatial scales, at which point the dynamo enters the slow growth phase [44]. This may be seen by the time delay for the larger scales of the power spectra to converge.…”

Section: Resultsmentioning

confidence: 99%

The small-scale turbulent dynamo in smoothed particle magnetohydrodynamics

Tricco

Price

Federrath

2016

J. Phys.: Conf. Ser.

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Abstract. Supersonic turbulence is believed to be at the heart of star formation. We have performed smoothed particle magnetohydrodynamics (SPMHD) simulations of the smallscale dynamo amplification of magnetic fields in supersonic turbulence. The calculations use isothermal gas driven at rms velocity of Mach 10 so that conditions are representative of starforming molecular clouds in the Milky Way. The growth of magnetic energy is followed for 10 orders in magnitude until it reaches saturation, a few percent of the kinetic energy. The results of our dynamo calculations are compared with results from grid-based methods, finding excellent agreement on their statistics and their qualitative behaviour. The simulations utilise the latest algorithmic developments we have developed, in particular, a new divergence cleaning approach to maintain the solenoidal constraint on the magnetic field and a method to reduce the numerical dissipation of the magnetic shock capturing scheme. We demonstrate that our divergence cleaning method may be used to achieve ∇ · B = 0 to machine precision, albeit at significant computational expense.

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“…Turk et al (2012) and Latif et al (2013d) performed cosmological magneto-hydrodynamical simulations and confirmed that the small-scale dynamo is operational during the formation of protogalaxies, and the operation of the smallscale dynamo has been confirmed even for turbulence driven by supernova explosions (Balsara et al 2004;Balsara & Kim 2005). Furthermore, substantial progress has been made in the theoretical understanding of the dynamo, including the regime at high Mach numbers, different types of turbulence, and a large range of magnetic Prandtl numbers (Federrath et al 2011a(Federrath et al , 2014Schober et al 2012b;Bovino et al 2013;Schleicher et al 2013a).…”

Section: Introductionmentioning

confidence: 88%

Magnetic fields in primordial accretion disks

Latif

Schleicher

2016

A&A

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Magnetic fields are considered a vital ingredient of contemporary star formation and may have been important during the formation of the first stars in the presence of an efficient amplification mechanism. Initial seed fields are provided via plasma fluctuations and are subsequently amplified by the small-scale dynamo, leading to a strong, tangled magnetic field. We explore how the magnetic field provided by the small-scale dynamo is further amplified via the α-Ω dynamo in a protostellar disk and assess its implications. For this purpose, we consider two characteristic cases, a typical Pop. III star with 10 M and an accretion rate of 10 −3 M yr −1 , and a supermassive star with 10 5 M and an accretion rate of 10 −1 M yr −1 . For the 10 M Pop. III star, we find that coherent magnetic fields can be produced on scales of at least 100 AU, which are sufficient to drive a jet with a luminosity of 100 L and a mass outflow rate of 10 −3.7 M yr −1 . For the supermassive star, the dynamical timescales in its environment are even shorter, implying smaller orbital timescales and an efficient magnetization out to at least 1000 AU. The jet luminosity corresponds to ∼10 6.0 L and a mass outflow rate of 10 −2.1 M yr −1 . We expect that the feedback from the supermassive star can have a relevant impact on its host galaxy.

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The Turbulent Dynamo in Highly Compressible Supersonic Plasmas

Cited by 123 publications

References 50 publications

Are the Formation and Abundances of Metal-poor Stars the Result of Dust Dynamics?

Are the Formation and Abundances of Metal-poor Stars the Result of Dust Dynamics?

The small-scale turbulent dynamo in smoothed particle magnetohydrodynamics

Magnetic fields in primordial accretion disks

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