Molecular Clouds: Formation and Disruption

Ballesteros-Paredes, Javier

doi:10.1023/b:astr.0000014950.77949.97

Cited by 9 publications

(8 citation statements)

References 51 publications

(52 reference statements)

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“…In numerical models, when energy feedback from stars is included, the cloud is blown out rapidly (see e.g. Ballesteros‐Paredes 2004a). However, it should be recognized that a detailed quantification of the star formation efficiency in turbulent simulations with open boundary conditions and stellar feedback is needed.…”

Section: Discussion: Virial Mass Virial Equilibrium and The Star Fmentioning

confidence: 99%

“…they are transient). Concerning the second assumption, the analysis by Ballesteros-Paredes & Vázquez-Semadeni (1997, see also Ballesteros-Paredes 1999 ) shows that the moment of inertia spans up to seven orders of magnitude (in absolute value) between the largest and the smallest clouds. Thus, it is not clear that an average for such a large scatter will be representative of the actual dynamics of the clouds.…”

Section: Fifth Assumption: Interstellar Clouds Are In Virial Equilibriummentioning

confidence: 99%

“…The possible inapplicability of these assumptions has been mentioned in passing in some previous papers (e.g. Ballesteros‐Paredes et al 1999a; Shadmehri, Vázquez‐Semadeni & Ballesteros‐Paredes 2002; Ballesteros‐Paredes 2004a) but no attention has been paid in general to its implications. Thus, in this paper the applicability of those assumptions for molecular clouds and their cores is discussed in detail.…”

Section: Introductionmentioning

confidence: 99%

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Six myths on the virial theorem for interstellar clouds

Ballesteros-Paredes¹

2006

Monthly Notices of the Royal Astronomical Society

121

117

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The interstellar medium is highly dynamic and turbulent. However, little or no attention has been paid in the literature to the implications that this fact has on the validity of at least six common assumptions on the virial theorem (VT), which are as follows. (i) The only role of turbulent motions within a cloud is to provide support against collapse; (ii) the surface terms are negligible compared to the volumetric ones; (iii) the gravitational term is a binding source for the clouds since it can be approximated by the gravitational energy; (iv) the sign of the second time‐derivative of the moment of inertia determines whether the cloud is contracting or expanding ; (v) interstellar clouds are in virial equilibrium (VE) and (vi) Larson's relations (mean density–size and velocity dispersion–size) are the observational proof that clouds are in VE. However, turbulent, supersonic interstellar clouds cannot fulfil these assumptions because turbulent fragmentation will induce flux of mass, moment and energy between the clouds and their environment, and will favour local collapse while it may also disrupt the clouds within a dynamical time‐scale. It is argued that although the observational and numerical evidence suggests that interstellar clouds are not in VE, the so‐called ‘virial mass’ estimations, which should actually be called ‘energy‐equipartition mass’ estimations, are good order of magnitude estimations of the actual mass of the clouds just because observational surveys will tend to detect interstellar clouds appearing to be close to energy equipartition. Similarly, order of magnitude estimations of the energy content of the clouds is reasonable. However, since clouds are actually out of VE, as suggested by asymmetrical line profiles, they should be transient entities. These results are compatible with observationally based estimations for rapid star formation, and call into question the models for the star formation efficiency based on clouds being in VE.

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Section: Discussion: Virial Mass Virial Equilibrium and The Star Fmentioning

confidence: 99%

Section: Fifth Assumption: Interstellar Clouds Are In Virial Equilibriummentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Six myths on the virial theorem for interstellar clouds

Ballesteros-Paredes¹

2006

Monthly Notices of the Royal Astronomical Society

121

117

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“…This cloud formation can occur within a few million years. Pringle et al (2001) also point out that GMCs are probably not in virial equilibrium, and note that their wind‐swept appearance suggests that they are anything but (Ballesteros‐Paredes 2004; Vázquez‐Semadeni et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Star formation in unbound giant molecular clouds: the origin of OB associations?

Clark

Bonnell

Zinnecker

et al. 2005

Monthly Notices of the Royal Astronomical Society

113

109

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We investigate the formation of star clusters in an unbound giant molecular cloud, where the supporting kinetic energy is twice as large as the cloud's self‐gravity. This cloud manages to form a series of star clusters and disperse, all within roughly two crossing times (10 Myr), supporting recent claims that star formation is a rapid process. Simple assumptions about the nature of the star formation occurring in the clusters allows us to place an estimate for the star formation efficiency at about 5–10 per cent, consistent with observations. We also propose that unbound clouds can act as a mechanism for forming OB associations. The clusters that form in the cloud behave as OB subgroups. These clusters are naturally expanding from one another due to the unbound nature of the flows that create them. The properties of the cloud we present here are consistent with those of classic OB associations.

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“…In comparison, typical values of the star formation efficiency observed in molecular clouds are only a few per cent (Myers et al 1986). When feedback from massive stars is included in the simulations, the measured efficiencies are significantly smaller (Passot, Vázquez‐Semadeni & Pouquet 1995), suggesting that massive stars are a key ingredient in regulating the efficiency of star formation (see also Ballesteros‐Paredes 2004, and references therein).…”

Section: Introductionmentioning

confidence: 99%

Tidal forces as a regulator of star formation in Taurus

Ballesteros-Paredes

Gómez

Loinard

et al. 2009

Monthly Notices of the Royal Astronomical Society: Letters

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Only a few molecular clouds in the solar neighbourhood exhibit the formation of only low-mass stars. Traditionally, these clouds have been assumed to be supported against more vigorous collapse by magnetic fields. The existence of strong magnetic fields in molecular clouds, however, poses serious problems for the formation of stars and of the clouds themselves. In this Letter, we review the three-dimensional structure and kinematics of Taurus -the archetype of a region forming only low-mass stars -as well as its orientation within the Milky Way. We conclude that the particularly low star formation efficiency in Taurus may naturally be explained by tidal forces from the Galaxy, with no need for magnetic regulation or stellar feedback.

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Molecular Clouds: Formation and Disruption

Cited by 9 publications

References 51 publications

Six myths on the virial theorem for interstellar clouds

Six myths on the virial theorem for interstellar clouds

Star formation in unbound giant molecular clouds: the origin of OB associations?

Tidal forces as a regulator of star formation in Taurus

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