Formation of structure in star-forming clouds

1990 ◽  
Vol 68 (9) ◽  
pp. 808-823
Author(s):  
Ralph E. Pudritz
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Interstellar Medium ◽  
Physical Properties ◽  
Molecular Clouds ◽  
Fundamental Theory ◽  
Wave Pressure ◽  
Star Forming ◽  
Effective Wave ◽  
Hydromagnetic Waves

Star formation occurs in massive, dense, molecular clouds in the interstellar medium. These clouds have a rich substructure consisting of dense clumps and extended filaments. Since stars only form within these dense clumps, any fundamental theory of star formation must predict their physical properties. This review focusses on the physics of molecular clouds and discusses in this context a particular mechanism for the formation of structure that is well supported by the observations. Strong hydromagnetic waves are likely to be excited in molecular clouds since it is observed that cloud magnetic fields have energy densities close to gravity. These waves support the cloud against global gravitational collapse by providing an effective wave "pressure". This review also shows that waves may control the formation of structure in molecular clouds.

scholarly journals CO and the Multiphase ISM

1997 ◽  
Vol 170 ◽  
pp. 25-32
Author(s):  
Christopher F. Mckee
Keyword(s):  
Mach Number ◽  
Magnetic Fields ◽  
Interstellar Medium ◽  
Molecular Clouds ◽  
Molecular Gas ◽  
Wave Pressure ◽  
Multiphase Structure ◽  
Co Observations

CO observations indicate that molecular clouds have a complex multiphase structure, and this is compared with the multiphase structure of the diffuse interstellar medium. The trace ionization within the molecular gas is governed primarily by UV photoionization. Magnetic fields contribute a significantly larger fraction of the pressure in molecular clouds than in the diffuse interstellar medium. Observations suggest that the total Alfvén Mach number, mAtot, of the turbulence in the diffuse ISM exceeds unity; Zeeman observations are consistent with mAtot ≲ 1 in molecular clouds, but more data are needed to verify this. Most molecular clouds are self-gravitating, and they can be modeled as multi-pressure polytropes with thermal, magnetic, and wave pressure. The pressure and density within self-gravitating clouds is regulated by the pressure in the surrounding diffuse ISM.

scholarly journals Radio observation of molecular clouds around the W5-East triggered star-forming region

2006 ◽  
Vol 2 (S237) ◽  
pp. 454-454
Author(s):  
Takahiro Niwa ◽  
Yoichi Itoh ◽  
Kengo Tachihara ◽  
Yumiko Oasa ◽  
Kazuyoshi Sunada ◽  
...  
Keyword(s):  
Star Formation ◽  
Physical Properties ◽  
Molecular Clouds ◽  
Mass Density ◽  
Hii Regions ◽  
Radio Observation ◽  
Hii Region ◽  
Star Forming ◽  
Cloud Evolution

It is known that most of stars are formed as clusters (Lada & Lada 2003, ARAA 41, L57) and clusters are formed by triggering. However, the relationships of molecular clouds' conditions and properties of formed stars by triggering is not well studied. To clarify differences between triggered and spontaneous star formation through physical properties of molecular clouds (e.g. mass, density, morphology), we observed the W5-East HII region. The W5-East HII region is located at 2 kpc and has a 10 pc extent of HII region. This region has 3 Bright Rimmed Clouds (BRCs; Sugitani et al. 1991, ApJS 77, S59), which are interface between HII regions and molecular clouds, and known as sites of triggered star formation. The molecular clouds surround the W5-East (Karr et al. 2003, ApJ, 595, 900), thus we expect molecular clouds morphology is affected by the HII region and the cloud evolution is supposed to be dominated by the expanding HII region.

scholarly journals Magnetic fields and star formation – new observational results

2006 ◽  
Vol 2 (S237) ◽  
pp. 141-147
Author(s):  
Richard M. Crutcher ◽  
Thomas H. Troland
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Fields ◽  
Interstellar Medium ◽  
Observational Data ◽  
Molecular Clouds ◽  
Dark Cloud ◽  
Magnetic Field Model ◽  
Field Lines ◽  
Cloud Cores

AbstractAlthough the subject of this meeting is triggered star formation in a turbulent interstellar medium, it remains unsettled what role magnetic fields play in the star formation process. This paper briefly reviews star formation model predictions for the ratio of mass to magnetic flux, describes how Zeeman observations can test these predictions, describes new results – an extensive OH Zeeman survey of dark cloud cores with the Arecibo telescope, and discusses the implications. Conclusions are that the new data support and extend the conclusions based on the older observational results – that observational data on magnetic fields in molecular clouds are consistent with the strong magnetic field model of star formation. In addition, the observational data on magnetic field strengths in the interstellar medium strongly suggest that molecular clouds must form primarily by accumulation of matter along field lines. Finally, a future observational project is described that could definitively test the ambipolar diffusion model for the formation of cores and hence of stars.

scholarly journals The Mopra DQS survey of the G333 region

2006 ◽  
Vol 2 (S237) ◽  
pp. 404-404
Author(s):  
M. R. Cunningham ◽  
I. Bains ◽  
N. Lo ◽  
T. Wong ◽  
M. G. Burton ◽  
...  
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Standard Model ◽  
Molecular Clouds ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Star Forming ◽  
Successful Model ◽  
The Standard Model ◽  
Forming Efficiency

Any successful model of star formation must be able to explain the low star forming efficiency of molecular clouds in our Galaxy. If the collapse of gas is regulated only by gravity, then the star formation rate should be orders of magnitude larger than the 1 M per year within our galaxy. The standard model invokes magnetic fields to slow down the rate of collapse, but does not explain star formation in cluster mode, or the lack of observed variations in the chemistry of molecular clouds if they are long-lived entities.

scholarly journals The Supernova – ISM/Star-formation interplay

2013 ◽  
Vol 9 (S296) ◽  
pp. 265-272
Author(s):  
Gerhard Hensler
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Molecular Clouds ◽  
Numerical Models ◽  
Evolutionary Models ◽  
Star Forming ◽  
Supernova Explosions ◽  
Representative Selection ◽  
Supernova Feedback ◽  
Selection Of

AbstractSupernovae are the most energetic stellar events and influence the interstellar medium by their gasdynamics and energetics. By this, both also affect the star formation positively and negatively. In this paper, we review the complexity of investigations aiming at understanding the interchange between supernova explosions with the star-forming molecular clouds. Commencing from analytical studies the paper advances to numerical models of supernova feedback from superbubble scales to galaxy structure. We also discuss parametrizations of star-formation and supernova-energy transfer efficiencies. Since evolutionary models from the interstellar medium to galaxies are numerous and are applying multiple recipes of these parameters, only a representative selection of studies can be discussed here.

scholarly journals Stochastic Star Formation and Magnetic Fields

1990 ◽  
Vol 140 ◽  
pp. 257-258
Author(s):  
J. V. Feitzinger ◽  
E. Harfst ◽  
J. Spicker
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Molecular Clouds ◽  
Large Scale ◽  
Spiral Structure ◽  
Galactic Plane ◽  
Molecular Gas ◽  
Cell Content ◽  
Star Forming ◽  
Flat Rotation Curves

The model of selfpropagating star formation uses local processes (200 pc cell size) in the interstellar medium to simulate the large scale cooperative behaviour of spiral structure in galaxies. The dynamic of the model galaxies is taken into account via the mass distribution and the resulting rotation curve; flat rotation curves are used. The interstellar medium is treated as a multiphase medium with appropriate cooling times and density history. The phases are: molecular gas, cool HI gas, warm intercloud and HII gas and hot coronal fountain gas. A detailed gas reshuffeling between the star forming cells in the plane and outside the galactic plane controls the cell content. Two processes working stochastically are incooperated: the building and the decay of molecular clouds and the star forming events in the molecular clouds.

HCL1 and HCL2 - low mass star formation in violent and quiet environments

2018 ◽  
Vol 14 (S345) ◽  
pp. 333-334
Author(s):  
L. Viktor Tóth ◽  
Orsolya Fehér ◽  
Mika Juvela ◽  
Julien Montillaud ◽  
Sándor Pintér
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Physical Properties ◽  
Mass Star ◽  
External Effects ◽  
Star Forming ◽  
Radio Line ◽  
Sky Survey ◽  
Low Mass

AbstractRecently a large number of Galactic cold clumps were located with the Planck all-sky survey. Our radio line observations have revealed the distribution and physical properties of the interstellar medium in dozens of PGCC sources. Clumps can be affected by many external effects. HCL1 (a.k.a. L1251) and HCL2 (which contains also TMC-1) are examples of low mass star forming clouds in violent and quiet environments.

scholarly journals Supernova Feedback on the Interstellar Medium and Star Formation

2010 ◽  
Vol 6 (S270) ◽  
pp. 309-317
Author(s):  
Gerhard Hensler
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Molecular Clouds ◽  
Numerical Models ◽  
Evolutionary Models ◽  
Star Forming ◽  
Hot Gas ◽  
Representative Selection ◽  
Supernova Feedback ◽  
Selection Of

AbstractSupernovae are the most energetic stellar events and influence the interstellar medium by their gasdynamics and energetics. By this, both also affect the star formation positively and negatively. In this paper, we review the development of the complexity of investigations aiming at understanding the interchange between supernovae and their released hot gas with the star-forming molecular clouds. Commencing from analytical studies the paper advances to numerical models of supernova feedback from superbubble scales to galaxy structure. We also discuss parametrizations of star-formation and supernova-energy transfer efficiencies. Since evolutionary models from the interstellar medium to galaxies are numerous and apply multiple recipes of these parameters, only a representative selection of studies can be discussed here.

AMBIPOLAR DIFFUSION AND TURBULENT MAGNETIC FIELDS IN MOLECULAR CLOUDS

2011 ◽  
Vol 26 (04) ◽  
pp. 235-249 ◽  
Author(s):  
MARTIN HOUDE ◽  
TALAYEH HEZAREH ◽  
HUA-BAI LI ◽  
THOMAS G. PHILLIPS
Keyword(s):  
Magnetic Fields ◽  
Molecular Clouds ◽  
Ambipolar Diffusion ◽  
Star Forming ◽  
Star Forming Regions ◽  
Spin Interactions ◽  
Line Narrowing ◽  
Weakly Ionized ◽  
Novel Method

We review the introduction and development of a novel method for the characterization of magnetic fields in star-forming regions. The technique is based on the comparison of spectral line profiles from coexistent neutral and ion molecular species commonly detected in molecular clouds, sites of star formation. Unlike other methods used to study magnetic fields in the cold interstellar medium, this ion/neutral technique is not based on spin interactions with the field. Instead, it relies on and takes advantage of the strong cyclotron coupling between the ions and magnetic fields, thus exposing what is probably the clearest observational manifestation of magnetic fields in the cold, weakly ionized gas that characterizes the interior of molecular clouds. We will show how recent development and modeling of the ensuing ion line narrowing effect leads to a determination of the ambipolar diffusion scale involving the turbulent component of magnetic fields in star-forming regions, as well as the strength of the ordered component of the magnetic field.

Discussion session on star formation, molecular clouds and the interstellar medium

1994 ◽  
Vol 217 (1-2) ◽  
pp. 227-230
Author(s):  
Karen M. Strom ◽  
Lennart Nordh ◽  
Eli Dwek
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Molecular Clouds ◽  
Discussion Session
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