scholarly journals The properties of clusters, and the orientation of magnetic fields relative to filaments, in magnetohydrodynamic simulations of colliding clouds

2021 ◽  
Vol 502 (2) ◽  
pp. 2285-2295
Author(s):  
C L Dobbs ◽  
J Wurster
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Strong Dependence ◽  
Stellar Clusters ◽  
Broad Agreement ◽  
Smoothed Particle ◽  
Grid Codes ◽  
Magnetohydrodynamic Simulations ◽  
Massive Clusters ◽  
The Magnetic Field

ABSTRACT We have performed Smoothed Particle Magneto-Hydrodynamics (SPMHD) calculations of colliding clouds to investigate the formation of massive stellar clusters, adopting a timestep criterion to prevent large divergence errors. We find that magnetic fields do not impede the formation of young massive clusters (YMCs), and the development of high star formation rates, although we do see a strong dependence of our results on the direction of the magnetic field. If the field is initially perpendicular to the collision, and sufficiently strong, we find that star formation is delayed, and the morphology of the resulting clusters is significantly altered. We relate this to the large amplification of the field with this initial orientation. We also see that filaments formed with this configuration are less dense. When the field is parallel to the collision, there is much less amplification of the field, dense filaments form, and the formation of clusters is similar to the purely hydrodynamical case. Our simulations reproduce the observed tendency for magnetic fields to be aligned perpendicularly to dense filaments, and parallel to low density filaments. Overall our results are in broad agreement with past work in this area using grid codes.

scholarly journals The Formation of Massive Stars

2010 ◽  
Vol 6 (S270) ◽  
pp. 57-64
Author(s):  
Ian A. Bonnell ◽  
Rowan J Smith
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Massive Star ◽  
Massive Stars ◽  
Cluster Formation ◽  
High Mass ◽  
Prestellar Cores ◽  
Stellar Mergers ◽  
Massive Clusters ◽  
Viable Mechanism

AbstractThere has been considerable progress in our understanding of how massive stars form but still much confusion as to why they form. Recent work from several sources has shown that the formation of massive stars through disc accretion, possibly aided by gravitational and Rayleigh-Taylor instabilities is a viable mechanism. Stellar mergers, on the other hand, are unlikely to occur in any but the most massive clusters and hence should not be a primary avenue for massive star formation. In contrast to this success, we are still uncertain as to how the mass that forms a massive star is accumulated. there are two possible mechanisms including the collapse of massive prestellar cores and competitive accretion in clusters. At present, there are theoretical and observational question marks as to the existence of high-mass prestellar cores. theoretically, such objects should fragment before they can attain a relaxed, centrally condensed and high-mass state necessary to form massive stars. Numerical simulations including cluster formation, feedback and magnetic fields have not found such objects but instead point to the continued accretion in a cluster potential as the primary mechanism to form high-mass stars. Feedback and magnetic fields act to slow the star formation process and will reduce the efficiencies from a purely dynamical collapse but otherwise appear to not significantly alter the process.

scholarly journals Magnetic fields at the onset of high-mass star formation

2018 ◽  
Vol 614 ◽  
pp. A64 ◽  
Author(s):  
H. Beuther ◽  
J. D. Soler ◽  
W. Vlemmings ◽  
H. Linz ◽  
Th. Henning ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Fields ◽  
Spectral Line ◽  
Function Analysis ◽  
High Mass ◽  
Mass Star ◽  
Starting Point ◽  
Polarized Emission ◽  
The Magnetic Field

Context. The importance of magnetic fields at the onset of star formation related to the early fragmentation and collapse processes is largely unexplored today. Aims. We want to understand the magnetic field properties at the earliest evolutionary stages of high-mass star formation. Methods. The Atacama Large Millimeter Array is used at 1.3 mm wavelength in full polarization mode to study the polarized emission, and, using this, the magnetic field morphologies and strengths of the high-mass starless region IRDC 18310-4. Results. Polarized emission is clearly detected in four sub-cores of the region; in general it shows a smooth distribution, also along elongated cores. Estimating the magnetic field strength via the Davis-Chandrasekhar-Fermi method and following a structure function analysis, we find comparably large magnetic field strengths between ~0.3–5.3 mG. Comparing the data to spectral line observations, the turbulent-to-magnetic energy ratio is low, indicating that turbulence does not significantly contribute to the stability of the gas clump. A mass-to-flux ratio around the critical value 1.0 – depending on column density – indicates that the region starts to collapse, which is consistent with the previous spectral line analysis of the region. Conclusions. While this high-mass region is collapsing and thus at the verge of star formation, the high magnetic field values and the smooth spatial structure indicate that the magnetic field is important for the fragmentation and collapse process. This single case study can only be the starting point for larger sample studies of magnetic fields at the onset of star formation.

scholarly journals Galactic flows and the formation of stellar clusters

2015 ◽  
Vol 12 (S316) ◽  
pp. 184-189
Author(s):  
Romas Smilgys ◽  
Ian A. Bonnell
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Cluster Formation ◽  
Stellar Clusters ◽  
Gravitational Instabilities ◽  
Merging Process ◽  
Original Region ◽  
Sph Simulation ◽  
Self Gravity ◽  
Massive Clusters

AbstractWe investigate the formation of stellar clusters from a Galactic scale SPH simulation. The simulation traces star formation over a 5.6 Myr timescale, with local gravitational instabilities resulting in ~ 105 solar masses of star formation in the form of sink particles. We investigate the time evolution of the physical properties of the forming clusters including their half-mass radii, their energies and the depletion time of the gas. Star formation is driven by the large scale flows which compress the gas to higher densities where self gravity takes over and collapse occurs. We show that the more massive clusters (up to ~ 2 × 104 solar masses) gather their material from of order 10 pc due to these large scale motions associated with the spiral arm passage and shock. The bulk of the gas becomes gravitationally bound near 1-2 Myr before sink formation, and in the absence of feedback, significant accretion ongoing on longer timescales. We trace the hierarchical merging process of cluster formation which naturally results in age spreads of order the crossing time of the original region which provides the gas reservoir for the cluster.

scholarly journals Massive core/star formation triggered by cloud–cloud collision: Effect of magnetic field

2020 ◽  
Author(s):  
Nirmit Sakre ◽  
Asao Habe ◽  
Alex R Pettitt ◽  
Takashi Okamoto
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Fields ◽  
Strong Magnetic Field ◽  
Molecular Clouds ◽  
Weak Magnetic Field ◽  
Dense Cores ◽  
Cloud Models ◽  
Low Mass ◽  
Magnetohydrodynamic Simulations

Abstract We study the effect of magnetic field on massive dense core formation in colliding unequal molecular clouds by performing magnetohydrodynamic simulations with sub-parsec resolution (0.015 pc) that can resolve the molecular cores. Initial clouds with the typical gas density of the molecular clouds are immersed in various uniform magnetic fields. The turbulent magnetic fields in the clouds consistent with the observation by Crutcher et al. (2010, ApJ, 725, 466) are generated by the internal turbulent gas motion before the collision, if the uniform magnetic field strength is 4.0 μG. The collision speed of 10 km s−1 is adopted, which is much larger than the sound speeds and the Alfvén speeds of the clouds. We identify gas clumps with gas densities greater than 5 × 10−20 g cm−3 as the dense cores and trace them throughout the simulations to investigate their mass evolution and gravitational boundness. We show that a greater number of massive, gravitationally bound cores are formed in the strong magnetic field (4.0 μG) models than the weak magnetic field (0.1 μG) models. This is partly because the strong magnetic field suppresses the spatial shifts of the shocked layer that should be caused by the nonlinear thin shell instability. The spatial shifts promote the formation of low-mass dense cores in the weak magnetic field models. The strong magnetic fields also support low-mass dense cores against gravitational collapse. We show that the numbers of massive, gravitationally bound cores formed in the strong magnetic field models are much larger than in the isolated, non-colliding cloud models, which are simulated for comparison. We discuss the implications of our numerical results on massive star formation.

scholarly journals Magnetic fields and Turbulence in Star Formation using Smoothed Particle Hydrodynamics

2010 ◽  
Vol 6 (S270) ◽  
pp. 169-177
Author(s):  
Daniel J. Price
Keyword(s):  
Star Formation ◽  
Mach Number ◽  
Magnetic Fields ◽  
Turbulent Flows ◽  
Smoothed Particle Hydrodynamics ◽  
Current State ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Smoothed Particle Hydrodynamics Method ◽  
The Relationship

AbstractFirstly, we give a historical overview of attempts to incorporate magnetic fields into the Smoothed Particle Hydrodynamics method by solving the equations of Magnetohydrodynamics (MHD), leading an honest assessment of the current state-of-the-art in terms of the limitations to performing realistic calculations of the star formation process. Secondly, we discuss the results of a recent comparison we have performed on simulations of driven, supersonic turbulence with SPH and Eulerian techniques. Finally we present some new results on the relationship between the density variance and the Mach number in supersonic turbulent flows, finding σ2ln ρ = ln(1 + b22 with b = 0.33 up to Mach 20, consistent with other numerical results at lower Mach number (Lemaster & Stone 2008) but inconsistent with observational constraints on σρ and in Taurus and IC5146.

scholarly journals Extra-Galactic Star Formation Revealed

2004 ◽  
Vol 221 ◽  
pp. 107-117
Author(s):  
Eva Schinnerer
Keyword(s):  
Star Formation ◽  
Early Universe ◽  
High Redshift ◽  
Gas Content ◽  
High Angular Resolution ◽  
Molecular Gas ◽  
Stellar Clusters ◽  
High Redshift Galaxies ◽  
Nearby Galaxies ◽  
Massive Clusters

High angular resolution observations of nearby galaxies in the optical using ground-based and space-based telescopes have not only revealed the presence of young stellar clusters, but also allowed to study their properties in various dynamical environments. These studies have shown that young massive clusters (YMCs) have typical masses of a few 1000 M⊙ and sizes of a few parsec irrespective of their site of formation (such as bulges, spiral arms, starburst rings, or mergers). This points toward a universal formation mechanism for these stellar clusters.Observations of the dust and gas content in high redshift galaxies allows one to study the reservoir for star formation in the early universe. These studies reveal extremely high star formation rates of a few 1000 M⊙ yr−1, while the distribution of the molecular gas still seems to be comparable to what is observed in the local universe. The detection of considerable amounts of molecular gas via its CO lines in the highest redshifted QSOs known today (up to z=6.4) indicates that star formation in the early universe has already produced considerable amounts of metals.

scholarly journals Magnetic fields and the dynamics of molecular clouds

1991 ◽  
Vol 147 ◽  
pp. 75-81
Author(s):  
J. L. Puget
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Velocity Field ◽  
Magnetic Fields ◽  
Molecular Clouds ◽  
Velocity Dispersion ◽  
Small Scale ◽  
Transverse Waves ◽  
Analytical Approximations ◽  
The Magnetic Field

Magnetic fields are believed to play an important role in the star formation process. Correlations in the velocity field in molecular filaments are indicative of dynamical interactions between clouds and parts within a cloud. The magnetic field is a likely candidate as the vector of such interactions. Perturbations of the field at large scales can feed the velocity dispersion within condensations at small scale. This mechanism is discussed in the framework of two simple analytical approximations describing transverse waves fed into plane parallel slabs.

Revealing magnetic fields towards massive protostars: a multi-scale approach using masers and dust

2018 ◽  
Vol 14 (A30) ◽  
pp. 111-112
Author(s):  
Daria Dall’Olio ◽  
W. H. T. Vlemmings ◽  
M. V. Persson
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Fields ◽  
Spatial Scales ◽  
High Mass ◽  
Small Scale ◽  
Evolutionary Stage ◽  
Mass Star ◽  
Filamentary Structure ◽  
The Magnetic Field

AbstractMagnetic fields play a significant role during star formation processes, hindering the fragmentation and the collapse of the parental cloud, and affecting the accretion mechanisms and feedback phenomena. However, several questions still need to be addressed to clarify the importance of magnetic fields at the onset of high-mass star formation, such as how strong they are and at what evolutionary stage and spatial scales their action becomes relevant. Furthermore, the magnetic field parameters are still poorly constrained especially at small scales, i.e. few astronomical units from the central object, where the accretion disc and the base of the outflow are located. Thus we need to probe magnetic fields at different scales, at different evolutionary steps and possibly with different tracers. We show that the magnetic field morphology around high-mass protostars can be successfully traced at different scales by observing maser and dust polarised emission. A confirmation that they are effective tools is indeed provided by our recent results from 6.7 GHz MERLIN observations of the massive protostar IRAS 18089-1732, where we find that the small-scale magnetic field probed by methanol masers is consistent with the large-scale magnetic field probed by dust (Dall’Olio et al. 2017 A&A 607, A111). Moreover we present results obtained from our ALMA Band 7 polarisation observations of G9.62+0.20, which is a massive star-forming region with a sequence of cores at different evolutionary stages (Dall’Olio et al. submitted to A&A). In this region we resolve several protostellar cores embedded in a bright and dusty filamentary structure. The magnetic field morphology and strength in different cores is related to the evolutionary sequence of the star formation process which is occurring across the filament.

scholarly journals The role of collision speed, cloud density, and turbulence in the formation of young massive clusters via cloud–cloud collisions

2020 ◽  
Vol 499 (1) ◽  
pp. 1099-1115
Author(s):  
Kong You Liow ◽  
Clare L Dobbs
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Conveyor Belt ◽  
Giant Molecular Clouds ◽  
Formation Mode ◽  
Smoothed Particle ◽  
Hydrodynamical Simulations ◽  
Massive Clusters ◽  
Cloud Density

ABSTRACT Young massive clusters (YMCs) are recently formed astronomical objects with unusually high star formation rates. We propose the collision of giant molecular clouds (GMCs) as a likely formation mechanism of YMCs, consistent with the YMC conveyor-belt formation mode concluded by other authors. We conducted smoothed particle hydrodynamical simulations of cloud–cloud collisions and explored the effect of the clouds’ collision speed, initial cloud density, and the level of cloud turbulence on the global star formation rate and the properties of the clusters formed from the collision. We show that greater collision speed, greater initial cloud density and lower turbulence increase the overall star formation rate and produce clusters with greater cluster mass. In general, collisions with relative velocity ≳ 25 km s−1, initial cloud density ≳ 250 cm−3, and turbulence of ≈2.5 km s−1 can produce massive clusters with properties resembling the observed Milky Way YMCs.

Magnetic fields along the star-formation sequence: bridging polarization-sensitive views

2018 ◽  
Vol 14 (A30) ◽  
pp. 97-99
Author(s):  
Anaëlle Maury ◽  
Swetlana Hubrig ◽  
Chat Hull
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Protoplanetary Disks ◽  
Young Stars ◽  
Formation Processes ◽  
Star Forming ◽  
Multi Scale ◽  
Wide Range ◽  
Observational Techniques ◽  
The Magnetic Field

AbstractIt is believed that magnetic fields play important roles in the processes leading to the formation of stars and planets. Polarimetry from optical to centimeter wavelengths has been the most powerful observing technique to study magnetic fields: the development of polarimetric capabilities on a wide range of observational facilities now allows to probe the magnetic field properties in various objects along the star formation sequence, from star-forming molecular clouds to young stars and their protoplanetary disks. However, the complexity of combining results from different observational techniques and facilities emphasizes the need to transcend historical barriers and bring together the various communities working with polarimetric observations. This Focus Meeting was a first step to compare observations of magnetic fields at the various evolutionary stages and physical scales involved in star formation processes, such that we can establish a coherent view of their key role in the multi-scale process of star formation.

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