Massive stars in subparsec rings around galactic centres

We consider the structure of self-gravitating marginally stable accretion discs in galactic centres in which a small fraction of the disc mass has been converted into protostars. We find that protostars accrete gaseous disc matter at prodigious rates. Mainly due to the stellar accretion luminosity, the disc heats up and thickens geometrically, shutting off further disc fragmentation. The existing protostars, however, continue to gain mass by gas accretion. As a result, the initial mass function for disc-born stars at distances R similar to 0.03-3 pc from the supermassive black hole should be top-heavy. The effect is most pronounced at around R similar to 0.1 pc. We suggest that this result explains observations of rings of young massive stars in our Galaxy and in M31, and we predict that more such rings will be discovered.