The Physical Nature of Dusty Dense Cores and the Origin of Stellar Masses

The development of a predictive theory of star formation is one of the prime goals of contemporary astrophysics. 
The problem of star formation is a very complex one and its solution depends critically on knowledge of certain 
empirical data.  In this colloquium I will discuss some of the key observational milestones that have recently 
been achieved in identifying and measuring the fundamental boundary and initial conditions that constrain this 
problem and that must be met by any complete theory of star formation.  I will begin with a brief review of what
is known about one of the most fundamental distributions in astrophysics, the stellar IMF.  I will then relate
 this knowledge to intriguing new results concerning the physical nature of dense cores on the verge of star 
formation in order to address the issue of the origin of stellar mass, the key unsolved mystery in the star 
formation process.  I will argue that these results suggest that the stellar IMF derives directly from the 
dense core mass function which itself originates in a process of simple thermal fragmentation in a pressurized 
medium.  The origin of stellar mass and the IMF may therefore be the result of the interplay of only a few very
basic and measurable physical processes.  This provides some optimism that a more complete and predictive theory 
of star formation may be within reach in the near future.