  Quasi-stationary flows of gas accreting onto a compact center are analyzed in
the framework of general-relativistic radiation hydrodynamics, under
assumptions of spherical symmetry and thin gas approximation. Numerical
investigation shows that luminosity, redshift and gas abundance are correlated.
The gas can constitute up to one third of the total mass of brightest
low-redshift sources, but its abundance goes down to 1/30 for sources with
luminosities close to the Eddington limit.
