The Initial Mass Function of Stars: Evidence for Uniformity in Variable Systems
Pavel Kroupa
The distribution of stellar masses that form in one star
formation event in a given volume of space is called the initial mass
function (IMF). The IMF has been estimated from low-mass brown dwarfs
to very massive stars. Combining IMF estimates for different
populations in which the stars can be observed individually unveils an
extraordinary uniformity of the IMF. This general insight appears to
hold for populations including present-day star formation in small
molecular clouds, rich and dense massive star-clusters forming in giant
clouds, through to ancient and metal-poor exotic stellar populations
that may be dominated by dark matter. This apparent universality of the
IMF is a challenge for star formation theory, because elementary
considerations suggest that the IMF ought to systematically vary with
star-forming conditions.
Institut für Theoretische Physik und Astrophysik,
Universität Kiel, D-24098 Kiel, Germany. E-mail:
pavel{at}astrophysik.uni-kiel.de