Schleicher, Dominik R. G.

[["dc.bibliographiccitation.artnumber","A22"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","572"],["dc.contributor.author","van Borm, C."],["dc.contributor.author","Bovino, Stefano"],["dc.contributor.author","Latif, A. H. M. Mahbub"],["dc.contributor.author","Schleicher, Dominik R. G."],["dc.contributor.author","Spaans, M."],["dc.contributor.author","Grassi, T."],["dc.date.accessioned","2018-11-07T09:31:57Z"],["dc.date.available","2018-11-07T09:31:57Z"],["dc.date.issued","2014"],["dc.description.abstract","Context. The seeds of the first supermassive black holes may have resulted from the direct collapse of hot primordial gas in greater than or similar to 10(4) K haloes, forming a supermassive or quasi- star as an intermediate stage. Aims. We explore the formation of a protostar resulting from the collapse of primordial gas in the presence of a strong Lyman- Werner radiation background. Particularly, we investigate the impact of turbulence and rotation on the fragmentation behaviour of the gas cloud. We accomplish this goal by varying the initial turbulent and rotational velocities. Methods. We performed 3D adaptive mesh refinement simulations with a resolution of 64 cells per Jeans length using the ENZO code, simulating the formation of a protostar up to unprecedentedly high central densities of 10(21) cm(-3) and spatial scales of a few solar radii. To achieve this goal, we employed the KROME package to improve modelling of the chemical and thermal processes. Results. We find that the physical properties of the simulated gas clouds become similar on small scales, irrespective of the initial amount of turbulence and rotation. After the highest level of refinement was reached, the simulations have been evolved for an additional similar to 5 freefall times. A single bound clump with a radius of 2 x 10(-2) AU and a mass of similar to 7 x 10(-2) M fi is formed at the end of each simulation, marking the onset of protostar formation. No strong fragmentation is observed by the end of the simulations, regardless of the initial amount of turbulence or rotation, and high accretion rates of a few solar masses per year are found. Conclusions. Given such high accretion rates, a quasi- star of 105 M fi is expected to form within 105 years."],["dc.description.sponsorship","Deutsche Forschungsgemeinschaft (DFG) [SFB 963 / 1]"],["dc.identifier.doi","10.1051/0004-6361/201424658"],["dc.identifier.fs","609689"],["dc.identifier.isi","000346101700037"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/11406"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/31640"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Effects of turbulence and rotation on protostar formation as a precursor of massive black holes"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A13"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","561"],["dc.contributor.author","Bovino, Stefano"],["dc.contributor.author","Schleicher, Dominik R. G."],["dc.contributor.author","Grassi, T."],["dc.date.accessioned","2018-11-07T09:46:39Z"],["dc.date.available","2018-11-07T09:46:39Z"],["dc.date.issued","2014"],["dc.description.abstract","Context. Population III stars are the first stars in the Universe to form at z = 20-30 out of a pure hydrogen and helium gas in minihalos of 10(5)-10(6) M-circle dot. Cooling and fragmentation is thus regulated via molecular hydrogen. At densities above 10(8) cm(-3), the three-body H-2 formation rates are particularly important for making the gas fully molecular. These rates were considered to be uncertain by at least a few orders of magnitude. Aims. We explore the impact of recently derived accurate three-body H-2 formation for three different minihalos, and compare them with the results obtained with three-body rates employed in previous other studies. Methods. The calculations were performed with the cosmological hydrodynamics code ENZO (release 2.2) coupled with the chemistry package KROME (including a network for primordial chemistry), which was previously shown to be accurate in high-resolution simulations. Results. While the new rates can shift the point where the gas becomes fully molecular, leading to a different thermal evolution, there is no trivial trend in the way this occurs. While one might naively expect the results to follow the rate coefficients trend, the behavior can vary depending on the dark-matter halo that is explored. Conclusions. We conclude that employing the correct three-body rates is about equally important as the use of appropriate initial conditions, and that the resulting thermal evolution needs to be calculated for every halo individually."],["dc.description.sponsorship","DFG [SCHL 1964/1-1]; CINECA consortium; [SFB 963/1]"],["dc.identifier.doi","10.1051/0004-6361/201322387"],["dc.identifier.fs","609680"],["dc.identifier.isi","000330584000013"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/10884"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/34928"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Primordial star formation: relative impact of H-2 three-body rates and initial conditions"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","013055"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","New Journal of Physics"],["dc.bibliographiccitation.volume","15"],["dc.contributor.affiliation","Bovino, S;"],["dc.contributor.affiliation","Schleicher, D R G;"],["dc.contributor.affiliation","Schober, J;"],["dc.contributor.author","Bovino, Stefano"],["dc.contributor.author","Schleicher, Dominik R. G."],["dc.contributor.author","Schober, Jennifer"],["dc.date.accessioned","2018-11-07T09:29:02Z"],["dc.date.available","2018-11-07T09:29:02Z"],["dc.date.issued","2013"],["dc.date.updated","2022-02-10T06:47:23Z"],["dc.description.abstract","The small-scale dynamo provides a highly efficient mechanism for the conversion of turbulent into magnetic energy. In astrophysical environments, such turbulence often occurs at high Mach numbers, implying steep slopes in the turbulent spectra. It is thus a central question whether the small-scale dynamo can amplify magnetic fields in the interstellar or intergalactic media, where such Mach numbers occur. To address this long-standing issue, we employ the Kazantsev model for turbulent magnetic field amplification, systematically exploring the effect of different turbulent slopes, as expected for Kolmogorov, Burgers, the Larson laws and results derived from numerical simulations. With the framework employed here, we give the first solution encompassing the complete range of magnetic Prandtl numbers, including Pm << 1, Pm similar to 1 and Pm >> 1. We derive scaling laws of the growth rate as a function of hydrodynamic and magnetic Reynolds number for Pm similar to 1 and Pm >> 1 for all types of turbulence. A central result concerns the regime of Pm similar to 1, where the magnetic field amplification rate increases rapidly as a function of Pm. This phenomenon occurs for all types of turbulence we have explored. We further find that the dynamo growth rate can be decreased by a few orders of magnitude for turbulence spectra steeper than Kolmogorov. We calculate the critical magnetic Reynolds number Rm(c) for magnetic field amplification, which is highest for the Burgers case. As expected, our calculation shows a linear behaviour of the amplification rate close to the threshold proportional to (Rm - Rm(c)). On the basis of the Kazantsev model, we therefore expect the existence of the small-scale dynamo for a given value of Pm as long as the magnetic Reynolds number is above the critical threshold."],["dc.description.sponsorship","Open-Access-Publikationsfonds 2013"],["dc.identifier.doi","10.1088/1367-2630/15/1/013055"],["dc.identifier.eissn","1367-2630"],["dc.identifier.fs","602614"],["dc.identifier.isi","000314341600002"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/8703"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/30926"],["dc.language.iso","en"],["dc.notes","PACS: 98.62.En Electric and magnetic fields\r\n\r\n95.30.Lz Hydrodynamics\r\n\r\n98.58.Ay Physical properties (abundances, electron density, magnetic fields, scintillation, scattering, kinematics, dynamics, turbulence, etc.)"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","IOP Publishing"],["dc.relation.issn","1367-2630"],["dc.relation.orgunit","Fakultät für Physik"],["dc.rights.uri","http://creativecommons.org/licenses/by/3.0/"],["dc.title","Turbulent magnetic field amplification from the smallest to the largest magnetic Prandtl numbers"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","023017"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","New Journal of Physics"],["dc.bibliographiccitation.volume","15"],["dc.contributor.affiliation","Schleicher, Dominik R G;"],["dc.contributor.affiliation","Schober, Jennifer;"],["dc.contributor.affiliation","Federrath, Christoph;"],["dc.contributor.affiliation","Bovino, Stefano;"],["dc.contributor.affiliation","Schmidt, Wolfram;"],["dc.contributor.author","Schleicher, Dominik R. G."],["dc.contributor.author","Schober, Jennifer"],["dc.contributor.author","Federrath, Christoph"],["dc.contributor.author","Bovino, Stefano"],["dc.contributor.author","Schmidt, Wolfram"],["dc.date.accessioned","2018-11-07T09:28:14Z"],["dc.date.available","2018-11-07T09:28:14Z"],["dc.date.issued","2013"],["dc.date.updated","2022-02-10T08:30:38Z"],["dc.description.abstract","The small-scale dynamo plays a substantial role in magnetizing the Universe under a large range of conditions, including subsonic turbulence at low Mach numbers, highly supersonic turbulence at high Mach numbers and a large range of magnetic Prandtl numbers Pm, i.e. the ratio of kinetic viscosity to magnetic resistivity. Low Mach numbers may, in particular, lead to the well-known, incompressible Kolmogorov turbulence, while for high Mach numbers, we are in the highly compressible regime, thus close to Burgers turbulence. In this paper, we explore whether in this large range of conditions, universal behavior can be expected. Our starting point is previous investigations in the kinematic regime. Here, analytic studies based on the Kazantsev model have shown that the behavior of the dynamo depends significantly on Pm and the type of turbulence, and numerical simulations indicate a strong dependence of the growth rate on the Mach number of the flow. Once the magnetic field saturates on the current amplification scale, backreactions occur and the growth is shifted to the next-larger scale. We employ a Fokker-Planck model to calculate the magnetic field amplification during the nonlinear regime, and find a resulting power-law growth that depends on the type of turbulence invoked. For Kolmogorov turbulence, we confirm previous results suggesting a linear growth of magnetic energy. For more general turbulent spectra, where the turbulent velocity scales with the characteristic length scale as u(e)alpha e(v) we find that the magnetic energy grows as (t/T-ed)(2v/( 1-v)), with t being the time coordinate and T-ed the eddy-turnover time on the forcing scale of turbulence. For Burgers turbulence, v = 1/2, quadratic rather than linear growth may thus be expected, as the spectral energy increases from smaller to larger scales more rapidly. The quadratic growth is due to the initially smaller growth rates obtained for Burgers turbulence. Similarly, we show that the characteristic length scale of the magnetic field grows as t(1/(1-v)) in the general case, implying t(3/2) for Kolmogorov and t(2) for Burgers turbulence. Overall, we find that high Mach numbers, as typically associated with steep spectra of turbulence, may break the previously postulated universality, and introduce a dependence on the environment also in the nonlinear regime."],["dc.description.sponsorship","Open-Access-Publikationsfonds 2013"],["dc.identifier.doi","10.1088/1367-2630/15/2/023017"],["dc.identifier.eissn","1367-2630"],["dc.identifier.fs","602615"],["dc.identifier.isi","000314868000004"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/8720"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/30727"],["dc.language.iso","en"],["dc.notes","47.40.Ki Supersonic and hypersonic flows\r\n\r\n47.27.E- Turbulence simulation and modeling\r\n\r\n47.40.Dc General subsonic flows"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","IOP Publishing"],["dc.relation.issn","1367-2630"],["dc.relation.orgunit","Fakultät für Physik"],["dc.rights.uri","http://creativecommons.org/licenses/by-nc-sa/3.0/"],["dc.title","The small-scale dynamo: breaking universality at high Mach numbers"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]