Zooming in to Massive Star Birth
  We present high resolution (0.2", 1000 AU) 1.3 mm ALMA observations of
massive infrared dark cloud clump, G028.37+00.07-C1, thought to harbor the
early stages of massive star formation. Using $\rm N_2D^+$(3-2) we resolve the
previously identified C1-S core, separating the bulk of its emission from two
nearby protostellar sources. C1-S is thus identified as a massive
($\sim50\:M_\odot$), compact ($\sim0.1\:$pc diameter) starless core, e.g., with
no signs of outflow activity. Being highly deuterated, this is a promising
candidate for a pre-stellar core on the verge of collapse. An analysis of its
dynamical state indicates a sub-virial velocity dispersion compared to a
trans-Alfv\'enic turbulent core model. However, virial equilibrium could be
achieved with sub-Alfv\'enic conditions involving $\sim2\:$mG magnetic field
strengths.
