  Keplerian accretion discs around massive black holes (MBHs) are
gravitationally unstable beyond a few hundredths of parsec and should collapse
to form stars. Indeed an accretion/star formation episode took place a few
millions years ago in the Galactic Center (GC). This raises the question of how
the disc can survive in AGN and quasars and continue to transport matter
towards the black hole. We study the accretion/star formation process, with one
aim in mind, to show that a spectrum similar to the observed AGN one can be
produced by the disc. We compute models of stationary accretion discs, both
continuous and clumpy. Continuous discs must be maintained in a state of
marginal stability for the rate of star formation to remain modest, so they
require additional heating and transport of angular momentum. Non-viscous
heating can be provided by stellar illumination, but momentum transport by
supernovae is insufficient to sustain a marginal state, except at the very
periphery of the disc. In clumpy discs it is possible to account for the
required accretion rate through interactions between clouds, but this model is
unsatisfactory as its parameters are tightly constrained without any physical
justification. Finally one must appeal to non-stationary discs with
intermittent accretion episodes like those that occurred in the GC, but such a
model is probably not applicable to luminous high redshift quasars neither to
radio-loud quasars.
