Investigating Magnetic Fields in High-Mass Pre-stellar Cores using ALMA

ABSTRACT :
High-mass pre-stellar cores (HMPSCs; >30 M⊙) are likely to be the precursors to high-mass (>8 M⊙) stars and are predicted to be in substantially different dynamical conditions by different high-mass star formation (HMSF) paradigms. The two primary paradigms for HMSF are (1) the core accretion model and (2) the competitive accretion model. The core accretion scenario forms near-virial cores that are supported by nonthermal mechanisms (i.e., B-fields and turbulence), while the competitive accretion scenario produces highly sub-virial cores accreting within fast collapsing clumps. Previous studies have estimated the gravitational and turbulent energies in HMPSC candidates, resulting in strong sub-virial states (virial parameter α <0.3) ignoring the B-field. Thus, the final piece of the energy puzzle lies in estimating the B-field strengths in these cores. Although a few HMPSC candidates have been identified in the literature, the role of B-fields in their formation is yet to be explored. Our pilot study using Atacama Large Millimeter/submillimeter Array (ALMA) dust polarization at 250 GHz finds a relatively strong B-field in an HMPSC candidate, resulting in a virial parameter α ~0.4, which suggests a gravitational collapse (as α <1). The degree of collapse is thus slower than that predicted from the competitive accretion, though it is not in equilibrium as predicted from the core accretion model. Thus, our results challenge the current paradigms of HMSF and necessitate additional investigation. We intend to study six more HMPSC candidates previously discovered from the ALMA-IMF Large Program to estimate their energy balance in a similar way, which will help us to understand their dynamical phases in the presence of B-fields, i.e., if the HMPSC candidates are in equilibrium (α ~1 and <2) or collapsing rapidly (with α <1). In this workshop, we will present the initial results of these HMPSC candidates.