The Dynamics of Massive Starless Cores

Intermediate- and high-mass stars may be born from relatively massive pre-stellar gas cores. The turbulent core accretion model invokes such cores as being in approximate virial equilibrium and in approximate pressure equilibrium with their surrounding clump medium. Alternatively, the competitive accretion model requires strongly sub-virial initial conditions that then lead to extensive fragmentation to the thermal Jeans scale, with intermediate- and high-mass stars forming later by competitive accretion. To test these models, Tan et al. have identified four massive (~100 M☉) clumps from mid-infrared extinction mapping of infrared dark clouds. They present ALMA observations of these four clumps that probe the N2D+ (3–2) line at 2.3 arcsecond resolution, find six N2D+ cores, and determine their dynamical state. The observed velocity dispersions and sizes are broadly consistent with the predictions of the turbulent core model of self-gravitating, magnetized, and virialized cores that are bounded by the high pressures of their surrounding clumps. However, in the most massive cores, their results suggest that moderately enhanced magnetic fields may be needed for the structures to be in virial and pressure equilibrium. Magnetically regulated core formation may thus be important in controlling the formation of massive cores, inhibiting their fragmentation, and thus helping to establish the stellar IMF.

Figure: ALMA data overlaid on an artist’s impression background. The ALMA data show two main cores as imaged by N2D+ emission. The core on the right is particularly bright and rounded, suggesting it is self-gravitating and poised to form a massive, single star. The other core appears more distorted and fragmented, potentially leading to the formation of multiple lower-mass stars.Credit: Bill Saxton & Alexandra Angelich (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO).

View Publication: The Dynamics of Massive Starless Cores with ALMA, Jonathan C. Tan (Florida), Shuo Kong (Florida), Michael J. Butler (Florida), Paola Caselli (Leeds), and Francesco Fontani (INAF), 2014 ApJ, 779, 96. (20 December 2013)

View 20 December 2013 Press Release

Added 21 Jan 2014

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