The stellar initial mass function

The IMF UNIVERSALITY HYPOTHESIS cannot be discarded despite the existence of the CLUSTER IMF THEOREM. This means that the currently existing star-formation theory fails to describe the stellar outcome. The IGIMF THEOREM, however, predicts a variation of galaxy-wide IMFs in dependence of the galaxy's star-formation rate even if the IMF UNIVERSALITY HYPOTHESIS is valid. Taking indirect evidence from chemical evolution studies and the IGIMF THEOREM into account, it follows, however, that bulges and elliptical galaxies may have had a top-heavy IMF. A break-down of the IMF UNIVERSALITY THEOREM would thus be evident in extreme galaxy-wide (≳ 10 M_⊙yr) star-formation events.