scholarly journals Three-dimensional MHD simulations of molecular cloud fragmentation regulated by gravity, ambipolar diffusion, and turbulence

2008 ◽  
Vol 4 (S259) ◽  
pp. 115-116
Author(s):  
Takahiro Kudoh ◽  
Shantanu Basu
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Time Scale ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Three Dimensional ◽  
Core Formation ◽  
Mhd Simulations ◽  
Dimensional Simulation

AbstractWe find that the star formation is accelerated by the supersonic turbulence in the magnetically dominated (subcritical) clouds. We employ a fully three-dimensional simulation to study the role of magnetic fields and ion-neutral friction in regulating gravitationally driven fragmentation of molecular clouds. The time-scale of collapsing core formation in subcritical clouds is a few ×107 years when starting with small subsonic perturbations. However, it is shortened to approximately several ×106 years by the supersonic flows in the clouds. We confirm that higher-spacial resolution simulations also show the same result.

scholarly journals Historical perspective on astrophysical MHD simulations

2010 ◽  
Vol 6 (S270) ◽  
pp. 7-17
Author(s):  
Michael L. Norman
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Numerical Simulations ◽  
Historical Development ◽  
Adaptive Mesh Refinement ◽  
Historical Perspective ◽  
Adaptive Mesh ◽  
Personal Perspective ◽  
Mhd Simulations

AbstractThis contribution contains the introductory remarks that I presented at IAU Symposium 270 on “Computational Star Formation” held in Barcelona, Spain, May 31–June 4, 2010. I discuss the historical development of numerical MHD methods in astrophysics from a personal perspective. The recent advent of robust, higher-order accurate MHD algorithms and adaptive mesh refinement numerical simulations promises to greatly improve our understanding of the role of magnetic fields in star formation.

scholarly journals Feedback Regulated Turbulence, Magnetic Fields, and Star Formation Rates in Galactic Disks

2015 ◽  
Vol 11 (S315) ◽  
pp. 38-41
Author(s):  
Chang-Goo Kim ◽  
Eve C. Ostriker
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Formation Rate ◽  
Three Dimensional ◽  
Vertical Direction ◽  
Quasi Equilibrium ◽  
Galactic Disks ◽  
Heating Rates ◽  
Mhd Simulations ◽  
Vertical Support

AbstractWe use three-dimensional magnetohydrodynamic (MHD) simulations to investigate the quasi-equilibrium states of galactic disks regulated by star formation feedback. We incorporate effects from massive-star feedback via time-varying heating rates and supernova (SN) explosions. We find that the disks in our simulations rapidly approach a quasi-steady state that satisfies vertical dynamical equilibrium. The star formation rate (SFR) surface density self-adjusts to provide the total momentum flux (pressure) in the vertical direction that matches the weight of the gas. We quantify feedback efficiency by measuring feedback yields, ηc≡ Pc/ΣSFR (in suitable units), for each pressure component. The turbulent and thermal feedback yields are the same for HD and MHD simulations, ηth ~ 1 and ηturb ~ 4, consistent with the theoretical expectations. In MHD simulations, turbulent magnetic fields are rapidly generated by turbulence, and saturate at a level corresponding to ηmag,t ~ 1. The presence of magnetic fields enhances the total feedback yield and therefore reduces the SFR, since the same vertical support can be supplied at a smaller SFR. We suggest further numerical calibrations and observational tests in terms of the feedback yields.

The role of magnetic field in the formation and evolution of filamentary molecular clouds

2018 ◽  
Vol 14 (A30) ◽  
pp. 100-100
Author(s):  
Shu-ichiro Inutsuka
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Mass Function ◽  
Convincing Evidence ◽  
Formation And Evolution ◽  
Cloud Cores ◽  
Compressed Layer

AbstractRecent observations have emphasized the importance of the formation and evolution of magnetized filamentary molecular clouds in the process of star formation. Theoretical and observational investigations have provided convincing evidence for the formation of molecular cloud cores by the gravitational fragmentation of filamentary molecular clouds. In this review we summarize our current understanding of various processes that are required in describing the filamentary molecular clouds. Especially we can explain a robust formation mechanism of filamentary molecular clouds in a shock compressed layer, which is in analogy to the making of “Sushi.” We also discuss the origin of the mass function of cores.

scholarly journals The Role of Magnetic Fields in Star Formation

2013 ◽  
Vol 9 (S302) ◽  
pp. 10-20 ◽  
Author(s):  
Ralph E. Pudritz ◽  
Mikhail Klassen ◽  
Helen Kirk ◽  
Daniel Seifried ◽  
Robi Banerjee
Keyword(s):  
Angular Momentum ◽  
Star Formation ◽  
Magnetic Fields ◽  
Molecular Clouds ◽  
Star Clusters ◽  
Young Stars ◽  
Giant Molecular Clouds ◽  
Jets And Outflows ◽  
Radiation Fields

AbstractStars are born in turbulent, magnetized filamentary molecular clouds, typically as members of star clusters. Several remarkable technical advances enable observations of magnetic structure and field strengths across many physical scales, from galactic scales on which giant molecular clouds (GMCs) are assembled, down to the surfaces of magnetized accreting young stars. These are shedding new light on the role of magnetic fields in star formation. Magnetic fields affect the gravitational fragmentation and formation of filamentary molecular clouds, the formation and fragmentation of magnetized disks, and finally to the shedding of excess angular momentum in jets and outflows from both the disks and young stars. Magnetic fields play a particularly important role in angular momentum transport on all of these scales. Numerical simulations have provided an important tool for tracking the complex process of the collapse and evolution of protostellar gas since several competing physical processes are at play - turbulence, gravity, MHD, and radiation fields. This paper focuses on the role of magnetic fields in three crucial regimes of star formation: the formation of star clusters emphasizing fragmentation, disk formation and the origin of early jets and outflows, to processes that control the spin evolution of young stars.

scholarly journals Testing the Paradigm of Low Mass Star Formation

2004 ◽  
Vol 221 ◽  
pp. 201-212
Author(s):  
Lee Hartmann
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Standard Model ◽  
Molecular Clouds ◽  
Class I ◽  
Stellar Systems ◽  
Mass Star ◽  
Core Formation ◽  
The Standard Model ◽  
Low Mass

Protostellar core formation is probably much more dynamic, and magnetic fields are probably much less important, than has been previously assumed in the standard model of low-mass star formation. This revised picture has important consequences: it is easier to understand the observed rapidity of star formation in molecular clouds; cores are more likely to have structures favoring high infall rates at early times, helping to explain the differences between Class 0 and Class I protostars; and core structure and asymmetry will strongly favor post-collapse fragmentation into binary and multiple stellar systems.

scholarly journals Theory of Cluster Formation: Effects of Magnetic Fields

2010 ◽  
Vol 6 (S270) ◽  
pp. 115-122 ◽  
Author(s):  
Fumitaka Nakamura ◽  
Zhi-Yun Li
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Molecular Clouds ◽  
Weak Magnetic Field ◽  
Thermal Emission ◽  
Strong Field ◽  
Cluster Formation ◽  
Free Fall ◽  
Field Lines

AbstractStars form predominantly in clusters inside dense clumps of molecular clouds that are both turbulent and magnetized. The typical size and mass of the cluster-forming clumps are ~1 pc and ~102 – 103 M⊙, respectively. Here, we discuss some recent progress on numerical simulations of clustered star formation in such parsec-scale dense clumps with emphasis on the role of magnetic fields. The simulations have shown that magnetic fields tend to slow down global gravitational collapse and thus star formation, especially in the presence of protostellar outflow feedback. Even a relatively weak magnetic field can retard star formation significantly, because the field is amplified by supersonic turbulence to an equipartition strength. However, in such a case, the distorted field component dominates the uniform one. In contrast, if the field is moderately-strong, the uniform component remains dominant. Such a difference in the magnetic structure is observed in simulated polarization maps of dust thermal emission. Recent polarization measurements show that the field lines in nearby cluster-forming clumps are spatially well-ordered, indicative of a rather strong field. In such strongly-magnetized clumps, star formation should proceed relatively slowly; it continues for at least several global free-fall times of the parent dense clump (tff ~ a few × 105 yr).

scholarly journals Can Multi-threaded Flux Tubes in Coronal Arcades Support a Magnetohydrodynamic Avalanche?

Solar Physics ◽  
2021 ◽  
Vol 296 (8) ◽  
Author(s):  
J. Threlfall ◽  
J. Reid ◽  
A. W. Hood
Keyword(s):  
Magnetic Fields ◽  
Three Dimensional ◽  
Coronal Loops ◽  
Flux Tubes ◽  
Single Thread ◽  
Mhd Instabilities ◽  
Mhd Instability ◽  
Mhd Simulations ◽  
Ideal Mhd ◽  
Model Geometry

AbstractMagnetohydrodynamic (MHD) instabilities allow energy to be released from stressed magnetic fields, commonly modelled in cylindrical flux tubes linking parallel planes, but, more recently, also in curved arcades containing flux tubes with both footpoints in the same photospheric plane. Uncurved cylindrical flux tubes containing multiple individual threads have been shown to be capable of sustaining an MHD avalanche, whereby a single unstable thread can destabilise many. We examine the properties of multi-threaded coronal loops, wherein each thread is created by photospheric driving in a realistic, curved coronal arcade structure (with both footpoints of each thread in the same plane). We use three-dimensional MHD simulations to study the evolution of single- and multi-threaded coronal loops, which become unstable and reconnect, while varying the driving velocity of individual threads. Experiments containing a single thread destabilise in a manner indicative of an ideal MHD instability and consistent with previous examples in the literature. The introduction of additional threads modifies this picture, with aspects of the model geometry and relative driving speeds of individual threads affecting the ability of any thread to destabilise others. In both single- and multi-threaded cases, continuous driving of the remnants of disrupted threads produces secondary, aperiodic bursts of energetic release.

scholarly journals Molecular and ionized gas kinematics in the GC Radio Arc

2016 ◽  
Vol 11 (S322) ◽  
pp. 133-136
Author(s):  
N. Butterfield ◽  
C.C. Lang ◽  
E. A. C. Mills ◽  
D. Ludovici ◽  
J. Ott ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Radio Continuum ◽  
Molecular Gas ◽  
The South ◽  
Ionized Gas ◽  
Molecular Emission ◽  
Gas Kinematics

AbstractWe present NH3 and H64α+H63α VLA observations of the Radio Arc region, including the M0.20 – 0.033 and G0.10 – 0.08 molecular clouds. These observations suggest the two velocity components of M0.20 – 0.033 are physically connected in the south. Additional ATCA observations suggest this connection is due to an expanding shell in the molecular gas, with the centroid located near the Quintuplet cluster. The G0.10 – 0.08 molecular cloud has little radio continuum, strong molecular emission, and abundant CH3OH masers, similar to a nearby molecular cloud with no star formation: M0.25+0.01. These features detected in G0.10 – 0.08 suggest dense molecular gas with no signs of current star formation.

scholarly journals Star–disc alignment in the protoplanetary discs: SPH simulation of the collapse of turbulent molecular cloud cores

2020 ◽  
Vol 492 (4) ◽  
pp. 5641-5654 ◽  
Author(s):  
Daisuke Takaishi ◽  
Yusuke Tsukamoto ◽  
Yasushi Suto
Keyword(s):  
Time Scale ◽  
Molecular Cloud ◽  
Three Dimensional ◽  
Gravitational Energy ◽  
Circumstellar Envelope ◽  
Rotation Axes ◽  
Particle Hydrodynamics ◽  
Disc Rotation ◽  
Cloud Cores ◽  
Sph Simulation

ABSTRACT We perform a series of three-dimensional smoothed particle hydrodynamics (SPH) simulations to study the evolution of the angle between the protostellar spin and the protoplanetary disc rotation axes (the star–disc angle ψsd) in turbulent molecular cloud cores. While ψsd at the protostar formation epoch exhibits broad distribution up to ∼130°, ψsd decreases (≲ 20°) in a time-scale of ∼104 yr. This time-scale of the star–disc alignment, talignment, corresponds basically to the mass doubling time of the central protostar, in which the protostar forgets its initial spin direction due to the mass accretion from the disc. Values of ψsd both at t = 102 yr and t = 105 yr after the protostar formation are independent of the ratios of thermal and turbulent energies to gravitational energy of the initial cloud cores: α = Ethermal/|Egravity| and γturb = Eturbulence/|Egravity|. We also find that a warped disc is possibly formed by the turbulent accretion flow from the circumstellar envelope.

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