Supermassive stars as the origin of the multiple populations in globular
  clusters
  Globular clusters (GCs) display anomalous light element abundances
(HeCNONaMgAl), resembling the yields of hot-hydrogen burning, but there is no
consensus yet on the origin of these ubiquitous multiple populations. We
present a model in which a super-massive star (SMS, >10^3 Msun) forms via
stellar collisions during GC formation and pollutes the intra-cluster medium.
The growth of the SMS finds a balance with the wind mass loss rate, such that
the SMS can produce a significant fraction of the total GC mass in processed
material, thereby overcoming the so-called mass-budget problem that plagues
other models. Because of continuous rejuvenation, the SMS acts as a
`conveyer-belt' of hot-hydrogen burning yields with (relatively) low He
abundances, in agreement with empirical constraints. Additionally, the amount
of processed material per unit of GC mass correlates with GC mass, addressing
the specific mass budget problem. We discuss uncertainties and tests of this
new self-enrichment scenario.
