Slow Star Formation in the Milky Way: Theory Meets Observations
  The observed star formation rate of the Milky Way can be explained by
applying a metallicity-dependent factor to convert CO luminosity to molecular
gas mass and a star formation efficiency per free-fall time that depends on the
virial parameter of a molecular cloud. These procedures also predict the trend
of star formation rate surface density with Galactocentric radius. The
efficiency per free-fall time variation with virial parameter plays the major
role in bringing theory into agreement with observations for the total star
formation rate, while the metallicity dependence of the CO luminosity to mass
conversion is most notable in the variation with Galactocentric radius.
Application of these changes resolves a factor of over 100 discrepancy between
observed and theoretical star formation rates that has been known for nearly 50
years.
