  Understanding the processes that determine the stellar Initial Mass Function
(IMF) is a critical unsolved problem, with profound implications for many areas
of astrophysics. In molecular clouds, stars are formed in cores, gas
condensations which are sufficiently dense that gravitational collapse converts
a large fraction of their mass into a star or small clutch of stars. In nearby
star-formation regions, the core mass function (CMF) is strikingly similar to
the IMF, suggesting that the shape of the IMF may simply be inherited from the
CMF. Here we present 1.3 mm observations, obtained with ALMA, the world's
largest interferometer, of the active star-formation region W43-MM1, which may
be more representative of the Galactic-disk regions where most stars form. The
unprecedented resolution of these observations reveals, for the first time, a
statistically robust CMF at high masses, with a slope that is markedly
shallower than the IMF. This seriously challenges our understanding of the
origin of the IMF.
