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Published online by Cambridge University Press: 04 August 2017
Many years ago M. Schmidt established the presence of a strong evolutionary effect in quasistellar objects (QSOs). Though this important problem is not yet fully resolved, there can be no doubt that in earlier epochs of the Universe evolution of the spatial density of QSOs (in the comoving coordinates) was much higher than it is now. Thus, for instance, the spatial density of the optically selected QSO is:
according to Schmidt (1977). Here τ = z/(l+z), whence, for instance, if z = 3, ρ ∼ 1000 ρ0, where ρ0 is the local density.