Rapid Formation of Molecular Clouds and Stars in the Solar Neighborhood

By L. Hartmann, J. Ballesteros-Paredes, E. Bergin. 2001

464 citations recorded by the source corpus.

We show how molecular clouds in the solar neighborhood might be formed and produce stars rapidly enough to explain stellar population ages, building on results from numerical simulations of the turbulent interstellar medium and general considerations of molecular gas formation. Observations of both star-forming regions and young, gas-free stellar associations indicate that most nearby molecular clouds form stars only over a short time span before dispersal; large-scale flows in the diffuse interstellar medium have the potential for forming clouds sufficiently rapidly and for producing stellar populations with ages much less than the lateral crossing times of their host molecular clouds. We identify four important factors for understanding rapid star formation and short cloud lifetimes. First, much of the accumulation and dispersal of clouds near the solar circle might occur in the atomic phase; only the high-density portion of a cloud's life cycle is spent in the molecular phase, thus helping to limit molecular cloud "lifetimes." Second, once a cloud achieves a high enough column density to form H2 and CO, gravitational forces become larger than typical interstellar pressure forces; thus, star formation can follow rapidly upon molecular gas formation and turbulent dissipation in limited areas of each cloud complex. Third, typical magnetic fields are not strong enough to prevent rapid cloud formation and gravitational collapse. Fourth, rapid dispersal of gas by newly formed stars, passing shock waves, and reduction of shielding by a small expansion of the cloud after the first events of star formation might limit the length of the star formation epoch and the lifetime of a cloud in its molecular state. This picture emphasizes the importance of large-scale boundary conditions for understanding molecular cloud formation and implies that star formation is a highly dynamic, rather than quasi-static, process and that the low Galactic star formation rate is due to low efficiency rather than slowed collapse in local regions.

Subfields: Astronomy and Astrophysics, Organic Chemistry, Physical and Theoretical Chemistry

View Paper: https://www.semanticscholar.org/paper/7c60b1b397b0f756142f5ceac13688d14fecc63c

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Citations in the corpus

UV-Optical Colors as Probes of Early-Type Galaxy Evolution (2006, background): “While most studies suggest that birth clouds are transient features with lifetimes of a few tens of Myrs (e.g. Blitz and Shu 1980; Hartmann et al. 2001), a recent work (Scoville and Wilson 2004) suggests that the low efficiency of star formation in these clouds implies significantly longer…”
Magnetically Regulated Star Formation in Three Dimensions: The Case of the Taurus Molecular Cloud Complex (2008, background): “In this case, the ages of the cores are set by the rate of mass condensation along the field lines, which may depend on the ill-understood process of turbulence replenishment in the diffuse gas, and may be accelerated by large-scale converging flows (Ballesteros et al. 1999; Hartmann et al. 2001).”
Slow Star Formation in Dense Gas: Evidence and Implications (2006, background): “Numerous authors have used various observational techniques to estimate tcl in clusters and GMCs (e.g., Elmegreen 2000; Hartmann et al. 2001; Tassis & Mouschovias 2004; Mouschovias et al. 2005; Tan et al. 2006; Ballesteros-Paredes & Hartmann 2006; Blitz et al. 2007).”
The Global Evolution of Giant Molecular Clouds. I. Model Formulation and Quasi-Equilibrium Behavior (2006, unknown): “…are probably dynamically disrupted in ∼ 1 crossing time, consistent with estimates of the lifetimes of small clouds in the solar neighborhood (e.g. Hartmann et al. 2001), although parts of them may endure in molecular phase and continue forming stars for longer periods of time even after the…”
Dust coagulation and fragmentation in molecular clouds. I. How collisions between dust aggregates alter the dust size distribution (2009, background): “In a study of molecular clouds in the solar neighborhood Hartmann et al. (2001) hint that the lifetime of molecular .10.”
The Birth of Molecular Clouds: Formation of Atomic Precursors in Colliding Flows (2006, background): “…the ”supersonic” line-widths are a consequence of cold regions moving with respect to each other within a warmer and more diffuse medium, but not a result of internal supersonic turbulence in the cold gas which eventually would be hosting star formation (Hartmann et al. 2001; Kwan & Sanders 1986).”
The lifecycle of molecular clouds in nearby star-forming disc galaxies (2019, background): “…lifetimes with similarly short values as in the present study (10−30 Myr) have been measured by counting clouds or classifying clouds based on their stellar content (e.g. Elmegreen 2000; Hartmann et al. 2001; Engargiola et al. 2003; Kawamura et al. 2009; Meidt et al. 2015; Corbelli et al. 2017).”
The Large- and Small-Scale Structures of Dust in the Star-forming Perseus Molecular Cloud (2006, background): “Large- or intermediate- scale triggered star formation (e.g., the ‘collect and collapse’ and ‘shells and rings’ scenarios in Elmegreen 1998) account for the formation of both the cloud and stars as well as the subsequent rapid dissipation of the cloud (see, e.g., Hartmann et al. 2001).”
STELLAR FEEDBACK IN MOLECULAR CLOUDS AND ITS INFLUENCE ON THE MASS FUNCTION OF YOUNG STAR CLUSTERS (2009, background): “We assume that the timescale for ISM removal is a few crossing times: ∆t ∼ (1−10)×τc (Elmegreen 2000, 2007; Hartmann et al. 2001; Tan et al. 2006; Krumholz & Tan 2007).”
The importance of the ortho:para H2 ratio for the deuteration of molecules during pre-protostellar collapse (2006, background): “[We note that Hartmann et al. (2001) estimated the ages of clouds in the solar vicinity as being of the order of 10 6 yr.]”