  We present a new infrared extinction study of Globule 2, the most opaque
molecular cloud core in the Coalsack complex. Using deep near-infrared imaging
observations obtained with the ESO NTT we are able to examine the structure of
the globule in significantly greater detail than previously possible. We find
the most prominent structural feature of this globule to be a strong central
ring of dust column density which was not evident in lower resolution studies
of this cloud. This ring represents a region of high density and pressure that
is likely a transient structure. For a spherical cloud geometry the ring would
correspond to a dense inner shell of high pressure that could not be in
dynamical equilibrium with its surroundings since there appear to be no sources
of pressure in the central regions of the cloud that could support the shell
against gravity and prevent its inward implosion. The timescale for the inward
collapse of the ring would be less than 2 x 10^5 years, suggesting that this
globule is in an extremely early stage of evolution, and perhaps caught in the
process of forming a centrally condensed dense core or Bok globule. Outside its
central regions the globule displays a well-behaved density profile whose shape
is very similar to that of a stable Bonnor-Ebert sphere. Using SEST we also
obtained a C18O spectrum toward the center of the cloud. The CO observation
indicates that the globule is a gravitationally bound object. Analysis of the
CO line profile reveals significant non-thermal gas motions likely due to
turbulence. As a whole the globule may be evolving to a global state of
quasi-static dynamical equilibrium in which thermal and turbulent pressure
balance gravity.
