Star formation through gravitational collapse and competitive accretion

By Ian A. Bonnell, Matthew R. Bate. 2006

320 citations recorded by the source corpus.

Competitive accretion, a process to explain the origin of the initial mass function (IMF), occurs when stars in a common gravitational potential accrete from a distributed gaseous component. Stars located near the centre of the potential benefit from the gravitational attraction of the full potential and accrete at much higher rates than do isolated stars. We show that concerns recently raised on the efficiency of competitive accretion are incorrect as they use globally averaged properties which are inappropriate for the detailed physics of a forming stellar cluster. A full treatment requires a realistic treatment of the cluster potential, the distribution of turbulent velocities and gas densities. Accreting gas does not travel at the global virial velocity of the system due to the velocity-sizescale relation inherent in turbulent gas and due to the lower velocity dispersion of small-N clusters in which much of the accretion occurs. Accretion occurs due to the effect of the local potential in funnelling gas down to the centre. Stars located in the gas-rich centres of such systems initially accrete from low relative velocity gas attaining larger masses before needing to accrete the higher velocity gas. Stars not in the centres of such potentials, or that enter the cluster later when the velocity dispersion is higher, do not accrete significantly and thus retain their low masses. In competitive accretion, most stars do not continue to accrete significantly such that their masses are set from the fragmentation process. It is the few stars which continue to accrete that become higher-mass stars. Competitive accretion is therefore likely to be responsible for the formation of higher-mass stars and can explain the mass distribution, mass segregation and binary frequency of these stars. Global kinematics of competitive accretion models include large-scale mass infall, with mean inflow velocities of the order of ≈0.5 km s -1 at scales of 0.5 pc, but infalling signatures are likely to be confused by the large tangential velocities and the velocity dispersion present. Finally, we discuss potential limitations of competitive accretion and conclude that competitive accretion is currently the most likely model for the origin of the high-mass end of the IMF.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/0468b08181b4ccf97404ec81231ad6ca9a4e3633

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Citations in the corpus

Dynamic star formation in the massive DR21 filament (2010, background): “Individual clumps (∼0.1–0.5 pc) fragment into hundreds of protostars, possibly competing for mass in the central regions of the cluster (Bonnell & Bate 2006).”
Fragmentation and mass segregation in the massive dense cores of Cygnus X (2009, background): “Due to the local, low values of the Jeans mass, the MDCs are actually expected to fragment and form clusters of protostars (Dobbs et al. 2005) which may later collect more mass in the central regions by competitive accretion (Bonnell & Bate 2006).”
Slow Star Formation in Dense Gas: Evidence and Implications (2006, background): “Feedback is not effective at slowing collapse or establishing an equilibrium, and only stops the star formation process at its end by rapidly unbinding the cluster (Bonnell & Bate 2006).”
Global hierarchical collapse in molecular clouds. Towards a comprehensive scenario (2019, background): “The GHC scenario is much closer to the competitive accretion one (e.g., Bonnell et al. 2001; Bonnell & Bate 2006), which already includes small- (at the single star or small stellar group level) and large-scale (at the level of the accretion flow onto the small star-forming sites) collapse flows.”
On the Rapid Collapse and Evolution of Molecular Clouds (2007, background): “Vázquez-Semadeni et al. (2005) and Bonnell & Bate (2006) also note the lack of stable equilibria in cluster-forming cores.”
H II REGIONS: WITNESSES TO MASSIVE STAR FORMATION (2010, background): “Unlike in the competitive accretion model (Bonnell & Bate 2006) where the most massive protostar continues to accrete from the common gas reservoir, in our model accretion is shut off by the subsequent fragmentation of the gas because the lower-mass companions intercept material that would…”
Using the minimum spanning tree to trace mass segregation (2009, background): “Or it may be primordial, where mass segregation is an outcome of the star formation process (Murray & Lin 1996; Bonnell & Bate 2006).”
Accretion disks in luminous young stellar objects (2015, background): “…collapse of a turbulent molecular core (McKee & Tan, 2002; Krumholz et al., 2009), those based on competitive accretion for core material (Bonnell & Bate, 2006), and those that propose Bondi-Hoyle accretion for the growth of the star (Keto, 2007) all predict the existence of a…”
RADIATION-HYDRODYNAMIC SIMULATIONS OF THE FORMATION OF ORION-LIKE STAR CLUSTERS. II. THE INITIAL MASS FUNCTION FROM WINDS, TURBULENCE, AND RADIATION (2012, background): “1 M , and massive stars subsequently grow from these small seeds by Bondi-Hoyle accretion (Bonnell et al. 1997, 2001a,b, 2004, 2006; Bonnell & Bate 2002, 2006; Bate & Bonnell 2005; Smith et al. 2009a,b).”
LOW VIRIAL PARAMETERS IN MOLECULAR CLOUDS: IMPLICATIONS FOR HIGH-MASS STAR FORMATION AND MAGNETIC FIELDS (2013, background): “The exact value of this threshold depends on model details (Krumholz et al. 2005), and it may be larger than the fiducial value by an order of magnitude (Bonnell & Bate 2006).”
The stellar and sub-stellar IMF of simple and composite populations (2011, background): “At least four competing theories have been developed: the competitive accretion scenario (Bonnell et al. 1998, 2004; Bonnell & Bate 2006), collisional merging (Bonnell & Bate 2002), the single core collapse model allowing isolated massive star formation (Krumholz et al. 2009), the…”
Toward Understanding Massive Star Formation (2007, background): “In response to this criticism, Bonnell & Bate (2006) argue that global initial collapse versus quasi-equilibrium support is not the issue, as their more recent SPH calculations start with initial conditions where the turbulent kinetic energy is close to the gravitational energy.”
COLLAPSE OF MASSIVE MAGNETIZED DENSE CORES USING RADIATION MAGNETOHYDRODYNAMICS: EARLY FRAGMENTATION INHIBITION (2011, background): “For instance, isothermal simulations (e.g., Bonnell et al. 2001; Bonnell & Bate 2006) and radiative calculations (Krumholz et al. 2007, 2009), magnetized ones (Wang et al. 2010; Hennebelle et al. 2011; Peters et al. 2011; Seifried et al. 2011) and even calculations including radiative ionization…”
Young Massive Star Clusters (2010, background): “This is generally consistent with simulations of cluster formation (Klessen 2001, Bonnell & Bate 2006).”
MODELING COLLAPSE AND ACCRETION IN TURBULENT GAS CLOUDS: IMPLEMENTATION AND COMPARISON OF SINK PARTICLES IN AMR AND SPH (2010, background): “…core and stellar initial mass functions (e.g., Klessen et al. 1998; Klessen 2001; Kroupa 2001; Padoan & Nordlund 2002; Chabrier 2003; Mac Low & Klessen 2004; Elmegreen & Scalo 2004; Larson 2005; Bonnell & Bate 2006; McKee & Ostriker 2007; Krumholz & Bonnell 2007; Hennebelle & Chabrier 2008, 2009).”