Star Formation in Massive Clusters via Bondi Accretion

Abstract

Essentially all stars form in giant molecular clouds (GMCs). However, inside GMCs, most of the gas does not participate in star formation; rather, denser gas accumulates in clumps in the GMC, with the bulk of the stars in a given GMC forming in a few of the most massive clumps. In the Milky Way, these clumps have masses $M_{\mathrm{cl}}\lesssim 5\times 10^{-2}$ of the GMC, radii $r_{\mathrm{cl}}\sim 1$pc, and free-fall times $τ_{\rm cl} \sim 2\times 10^5\yr$. We show that clumps inside giant molecular clouds should accrete at a modified Bondi accretion rate, which depends on clump mass as ${\dot{M}}_{\mathrm{cl}}\sim M_{\mathrm{cl}}^{5/4}$. This rate is initially rather slow, usually slower than the initial star formation rate inside the clump (we adopt the common assumption that inside the clump, ${\dot{M}}_{\ast }={\epsilon }_{\mathrm{ff}}{M}_{\mathrm{cl}}/{\tau }_{\mathrm{cl}}$, with ${\epsilon }_{\mathrm{ff}}\approx 0.017$). However, after $\sim 2$ GMC free-fall times ${\tau }_{\mathrm{GMC}}$, the clump accretion rate accelerates rapidly; formally, the clump can accrete the entire GMC in $\sim 3{\tau }_{\mathrm{GMC}}$. At the same time, the star formation rate accelerates, tracking the Bondi accretion rate. If the GMC is disrupted by feedback from the largest clump, half the stars in that clump form in the final $\taug$ before the GMC is disrupted. The theory predicts that the distribution of effective star formation rates, measured per GMC free-fall time, is broad, ranging from $\sim 0.001$ up to 0.1 or larger and that the mass spectrum of star clusters is flatter than that of clumps, consistent with observations.

8 pages, 5 figures, submitted to ApJ

References in corpus (5)

• On the Star Formation Rates in Molecular Clouds
• A Molecular Star Formation Law in the Atomic Gas Dominated Regime in Nearby Galaxies
• The Scale Dependence of the Molecular Gas Depletion Time in M33
• Giant Molecular Clouds in M31: I - Molecular Cloud Properties
• Supersonic turbulence, filamentary accretion,and the rapid assembly of massive stars and disks

Cited by in corpus (11)

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• Numerical Calibration of the HCN$-$Star Formation Correlation
• Star cluster formation with stellar feedback and large-scale inflow
• Bondi-Hoyle Accretion in an Isothermal Magnetized Plasma
• The Accelerating Pace of Star Formation
• Cluster formation in molecular clouds: I. stellar populations, star formation rates, and ionizing radiation
• On the thermal structure of the proto-Super Star Cluster 13 in NGC 253
• The physical and chemical structure of high-mass star-forming regions. Unraveling chemical complexity with the NOEMA large program "CORE"
• Network of Star Formation: Fragmentation controlled by scale-dependent turbulent pressure and accretion onto the massive cores revealed in the Cygnus-X GMC complex