Direct collapse black holes are generally thought to be extremely rare objects in the high-redshift Universe, because the three fundamental conditions for their formation (see above in section Formation) are challenging to be met all together in the same gas cloud. Current cosmological simulations suggest that DCBHs could be as rare as only about 1 per cubic giga parsec at redshift 15. The prediction on their number density is highly dependent on the minimum flux of Lyman–Werner photons required for their formation and can be as large as ~10 DCBHs per cubic gigaparsec in the most optimistic scenarios.