Theory of Star Formation

By C. McKee, E. Ostriker. 2007

1,792 citations recorded by the source corpus.

We review current understanding of star formation, outlining an overall theoretical framework and the observations that motivate it. A conception of star formation has emerged in which turbulence plays a dual role, both creating overdensities to initiate gravitational contraction or collapse, and countering the effects of gravity in these overdense regions. The key dynamical processes involved in star formation—turbulence, magnetic fields, and self-gravity— are highly nonlinear and multidimensional. Physical arguments are used to identify and explain the features and scalings involved in star formation, and results from numerical simulations are used to quantify these effects. We divide star formation into large-scale and small-scale regimes and review each in turn. Large scales range from galaxies to giant molecular clouds (GMCs) and their substructures. Important problems include how GMCs form and evolve, what determines the star formation rate (SFR), and what determines the initial mass function (IMF). Small scales range from dense cores to the protostellar systems they beget. We discuss formation of both low- and high-mass stars, including ongoing accretion. The development of winds and outflows is increasingly well understood, as are the mechanisms governing angular momentum transport in disks. Although outstanding questions remain, the framework is now in place to build a comprehensive theory of star formation that will be tested by the next generation of telescopes.

Subfields: Astronomy and Astrophysics, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/95fdb251bac6a60de90f93a5da8e55d78bd2d85c

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Citations in the corpus

The CO-H2 Conversion Factor in Disc Galaxies and Mergers (2011, methodology): “In unresolved GMCs we can estimate this heating rate based on numerical experiments on the rate of turbulent dissipation:Γturb ≈ 1.5 × σ3/R, whereR is the GMC radius (McKee & Ostriker 2007).”
Multiple populations in globular clusters (2012, background): “Various authors (see the review by McKee & Ostriker 2007 and references therein) suggest that star formation within a giant molecular cloud occurs on timescales comparable to a few times (1-3) the crossing time (roughly, tcr ∼ 10 M 1/4 6 Myr, where M6 is the mass of the cloud in units of 10 6 M⊙).”
Global hierarchical collapse in molecular clouds. Towards a comprehensive scenario (2019, background): “…scaling relation, σv ∝ R1/2 (or, equivalently, L ≈ cst.) is assumed to be the result of supersonic turbulence with a Burgers’ energy spectrum of the form E(k) ∝ k−2 (e.g., McKee & Ostriker 2007), where E(k) is the specific kinetic energy per wavenumber interval, and k is the wavenumber.”
PHIBSS: MOLECULAR GAS CONTENT AND SCALING RELATIONS IN z ∼ 1–3 MASSIVE, MAIN-SEQUENCE STAR-FORMING GALAXIES (2012, background): “……10 5 cm -3 ) and cool (Tgas~10-50 K), turbulent ‘giant molecular clouds’ near virial equilibrium on large scales (GMCs: Solomon et al. 1987, Blitz 1993, McKee & Ostriker 2007, Bigiel et al. 2008, Leroy et al. 2008, Bolatto et al. 2008, Krumholz, Leroy & McKee 2011, Kennicutt & Evans 2012).”
The density variance–Mach number relation in supersonic turbulence – I. Isothermal, magnetized gas (2012, background): “Conversely, the importance of magnetic fields in the star formation process is still inconclusive, despite decades of research (Mouschovias & Ciolek 1999; McKee & Ostriker 2007; Crutcher, Hakobian & Troland 2009; Crutcher et al. 2010; Bertram et al. 2012).”
Modelling CO formation in the turbulent interstellar medium (2009, background): “…dense clouds of molecular gas (Lada & Lada 2003), understanding how these clouds form, and how and why they then form stars, is crucial if we are to develop any real understanding of the process of star formation (Mac Low & Klessen 2004; Ballesteros-Paredes et al. 2007; McKee & Ostriker 2007).”
ENVIRONMENTAL DEPENDENCE OF THE KENNICUTT–SCHMIDT RELATION IN GALAXIES (2010, result): “This choice provides a marginally better overall fit to the observations, and is also consistent with estimates of the gas clumping factor deep inside molecular clouds (McKee & Ostriker 2007).”
THE DARK MOLECULAR GAS (2010, background): “27 in McKee & Ostriker 2007).”
A CONSTANT MOLECULAR GAS DEPLETION TIME IN NEARBY DISK GALAXIES (2011, background): “The relatively low efficiency of star formation per dynamical time requires that the star formation process be more complex than simple gravitational collapse (e.g., McKee & Ostriker 2007).”
Modeling UV Radiation Feedback from Massive Stars. II. Dispersal of Star-forming Giant Molecular Clouds by Photoionization and Radiation Pressure (2018, background): “A number of theoretical studies have invoked the destructive role of UV radiation feedback to explain the observed SFEs and lifetimes of GMCs (see reviews by McKee & Ostriker 2007; Krumholz et al. 2014).”
NUMERICAL TESTS OF FAST RECONNECTION IN WEAKLY STOCHASTIC MAGNETIC FIELDS (2009, background): “This is a relieving news for the interstellar medium, star formation and Solar simulations (Ostriker et al. 2001; McKee & Ostriker 2007), as numerical reconnection in MHD codes is fast.”
Three-phase Interstellar Medium in Galaxies Resolving Evolution with Star Formation and Supernova Feedback (TIGRESS): Algorithms, Fiducial Model, and Convergence (2016, background): “Feedback from massive young stars plays a crucial role in regulating star formation and the properties of the interstellar medium (ISM) at all scales (e.g., McKee & Ostriker 2007; Krumholz et al. 2014).”
The birth of a galaxy – II. The role of radiation pressure (2012, background): “Stellar radiation from massive stars and their supernova (SN) explosions significantly alter the surrounding interstellar medium (ISM) and, thus, subsequent star formation in the host galaxy (for a review, see McKee & Ostriker 2007).”
The structure of the interstellar medium of star‐forming galaxies (2011, background): “…produced by star formation, but comes from gravitational cascades from larger scales or instabilities that can tap into the differential rotation in galaxies (see e.g. Mac Low & Klessen 2004; McKee & Ostriker 2007, and references therein, for reviews of ISM turbulence and stellar feedback).”
Dusty Star Forming Galaxies at High Redshift (2014, background): “…within the Milky Way occupy a relatively limited range (i.e. gas temperatures, GMC velocity dispersion and cloud surface density), this result is not terribly surprising (Maloney and Black, 1988; McKee and Ostriker, 2007; Feldmann et al., 2012a; Shetty et al., 2011b; Narayanan and Hopkins, 2013).”
THE BOLOCAM GALACTIC PLANE SURVEY: SURVEY DESCRIPTION AND DATA REDUCTION (2010, methodology): “Following Williams et al. (2000) and McKee & Ostriker (2007), we use the term “core” to refer to a very dense region destined to form an individual star or small multiple star system and the term “clump” to refer to a region likely to form a group or cluster of stars.”
On the fraction of star formation occurring in bound stellar clusters (2012, methodology): “…and theory show that star formation is likely a universal process (e.g. Elmegreen & Efremov 1997; Kennicutt 1998; Elmegreen 2002; Krumholz & McKee 2005; McKee & Ostriker 2007), in the sense that the physics of how a collapsing cloud converts its gas to stars seem to hold everywhere in the Universe.”
Cosmic evolution of the atomic and molecular gas contents of galaxies (2011, methodology): “…models for the evolution of theHI and H2 gas content of galaxies, taking advantage of the development of realistic SF models (e.g. Mac Low & Klessen 2004; Pelupessy et al. 2006; Blitz & Rosolowsky 2006; Krumholz et al. 2009; Pelupessy & Papadopoulos 2009; see McKee & Ostriker 2007 for a review).”
MODELING COLLAPSE AND ACCRETION IN TURBULENT GAS CLOUDS: IMPLEMENTATION AND COMPARISON OF SINK PARTICLES IN AMR AND SPH (2010, background): “Supersonic turbulence, in particular, plays an important role in shaping the cloud structure, and in controlling star formation, because it creates the seeds for local gravitational collapse (Elmegreen & Scalo 2004; Scalo & Elmegreen 2004; Mac Low & Klessen 2004; McKee & Ostriker 2007).”