  Understanding the origin of stellar masses is a key problem in astrophysics.
In the solar neighborhood, the mass distribution of stars follows a seemingly
universal pattern. In the centre of the Milky Way, however, there are
indications for strong deviations and the same may be true for the nuclei of
distant starburst galaxies. Here we present the first numerical hydrodynamical
calculations of stars formed in a molecular region with chemical and
thermodynamic properties similar to those of warm and dusty circum-nuclear
starburst regions. The resulting IMF is top-heavy with a peak at ~ 15 Msun, a
sharp turn-down below 7 Msun and a power-law decline at high masses. We find a
natural explanation for our results in terms of the temperature dependence of
the Jeans mass, with collapse occuring at a temperature of ~ 100 K and an H2
density of a few times 10^5 cm^-3, and discuss possible implications for galaxy
formation and evolution.
