Small-scale dynamo action during the formation of the first stars and galaxies - I. The ideal MHD limit

By D. Schleicher, Robi Banerjee, S. Sur, T. Arshakian, Ralf Klessen, Rainer Beck, M. Spaans. 2010

147 citations recorded by the source corpus.

We explore the amplification of magnetic seeds during the formation of the first stars and galaxies. During gravitational collapse, turbulence is created from accretion shocks, which may act to amplify weak magnetic fields in the protostellar cloud. Numerical simulations showed that such turbulence is sub-sonic in the first star-forming minihalos, and highly supersonic in the first galaxies with virial temperatures larger than 10(4) K. We investigate the magnetic field amplification during the collapse both for Kolmogorov and Burgers-type turbulence with a semi-analytic model that incorporates the effects of gravitational compression and small-scale dynamo amplification. We find that the magnetic field may be substantially amplified before the formation of a disk. On scales of 1/10 of the Jeans length, saturation occurs after similar to 10(8) yr. Although the saturation behaviour of the small-scale dynamo is still somewhat uncertain, we expect a saturation field strength of the order similar to 10 (7)n(0.5) G in the first star-forming halos, with n the number density in cgs units. In the first galaxies with higher turbulent velocities, the magnetic field strength may be increased by an order of magnitude, and saturation may occur after 10(6)-10(7) yr. In the Kolmogorov case, the magnetic field strength on the integral scale (i.e. the scale with most magnetic power) is higher due to the characteristic power-law indices, but the difference is less than a factor of 2 in the saturated phase. Our results thus indicate that the precise scaling of the turbulent velocity with length scale is of minor importance. They further imply that magnetic fields will be significantly enhanced before the formation of a protostellar disk, where they may change the fragmentation properties of the gas and the accretion rate.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/48360ba680fc340d59179df8c3acf3dc32502408

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Citations in the corpus

Formation and evolution of primordial protostellar systems (2012, background): “Another complication is given by magnetic fields, which are thought to be important in minihaloes (e.g. Machida, Matsumoto & Inutsuka 2008; Xu et al. 2008; Schleicher et al. 2009, 2010; Sur et al. 2010; Federrath et al. 2011; Schober et al. 2012; Turk et al. 2012).”
THE MASS SPECTRUM OF THE FIRST STARS (2014, background): “It has also been suggested that the magnetic field will be amplified very efficiently by turbulent motion in the minihalo (e.g., Schleicher et al. 2010; Schober et al. 2012).”
THE STAR FORMATION RATE OF TURBULENT MAGNETIZED CLOUDS: COMPARING THEORY, SIMULATIONS, AND OBSERVATIONS (2012, background): “In the more realistic case of turbulent flows, field lines become tangled, and the B–ρ correlation is a combination of compression of field lines and turbulent dynamo amplification (Schleicher et al. 2010; Sur et al. 2010; Federrath et al. 2011c; Turk et al. 2012; Schober et al. 2012).”
The density variance–Mach number relation in supersonic turbulence – I. Isothermal, magnetized gas (2012, background): “Aside from these reports, if the magnetic flux is not conserved, but increases due to turbulent dynamo amplification during compression, α can become larger than the values quoted above, depending on the Reynolds numbers of the gas (Schleicher et al. 2010; Sur et al. 2010; Federrath et al. 2011).”
A NEW JEANS RESOLUTION CRITERION FOR (M)HD SIMULATIONS OF SELF-GRAVITATING GAS: APPLICATION TO MAGNETIC FIELD AMPLIFICATION BY GRAVITY-DRIVEN TURBULENCE (2011, methodology): “The connection between gravity-driven turbulence and magnetic field amplification has also been suggested recently in a model by Schleicher et al. (2010) and confirmed numerically in Sur et al. (2010).”
On the universality of supersonic turbulence (2013, background): “Even the early Universe was likely dominated by supersonic turbulence when the first cosmic haloes started to contract to form the first galaxies (Abel, Bryan & Norman 2002; Greif et al. 2008; Wise, Turk & Abel 2008; Schleicher et al. 2010).”
The First Stars (2012, methodology): “Schleicher et al. (2010) study both Kolmogorov turbulence, with β = 1/3 and Burgers turbulence, with β = 1/2, and show that in both cases, amplification of a weak initial seed field occurs rapidly, and that the field reaches saturation on all but the largest scales at an early point during the…”
FORMATION OF MASSIVE PRIMORDIAL STARS: INTERMITTENT UV FEEDBACK WITH EPISODIC MASS ACCRETION (2015, background): “However, theoretical studies predict that the field strength can be significantly amplified by the turbulent dynamo process during early collapse (e.g., Schleicher et al. 2010; Turk et al. 2012).”
Building up the Population III initial mass function from cosmological initial conditions (2016, background): “…as well as the rate of stellar ejections and mergers (e.g. Machida et al. 2006; Xu et al. 2008; Machida & Doi 2013), particularly if tiny cosmological seed fields can be rapidly amplified within the minihalo through the small-scale dynamo (e.g. Schleicher et al. 2010; Schober et al. 2012).”
THE GENERATION OF STRONG MAGNETIC FIELDS DURING THE FORMATION OF THE FIRST STARS (2010, methodology): “In the context of the first stars and the first galaxies, dynamo amplification of small seed fields has been previously addressed using semianalytic models [14].”
Possible indirect confirmation of the existence of Pop III massive stars by gravitational wave (2014, background): “According to their results, the turbulent motions driven in the galaxy formation might increase the magnetic field up to <10−6 G (Schleicher et al. 2010; Sur et al. 2010; Schober et al. 2012; Turk et al. 2012), which is similar value to that in molecular clouds of the galaxy.”
Cosmological Magnetic Fields: Their Generation, Evolution and Observation (2013, methodology): “Ryu et al (2008); Schleicher et al (2010) argue that the small-scale turbulent dynamo operating in the IGM during the collapse of proto-galaxies amplifies initial seed magnetic fields up to equipartition with the turbulent energy on time scales much shorter than the dynamical time scale, see also…”