How is a massive black hole created in a galaxy center in the first place?

 

Seed_scheme
Possible routes to black hole formation. From Volonteri et al. Proceedings of the IAU symposium No. 319

Models of massive black hole formation must explain both the advent of the first luminous quasars, why some galaxies host a central black hole, and some others do not.

Gas density (left) and metallicity (right) maps at z = 6.69 in a 10 Mpc cosmological simulation where black hole formation has been implemented based on models hinging on low-metallicity stars. The halos hosting a black hole are highlighted with circles. Black hole formation walks a fine line: the necessity of having high gas densities selects biased regions, the criterion of low-metallicity works in the opposite way. Black holes form in biased regions just before they experience a star formation event.