Can supermassive black hole seeds form in galaxy mergers?

It has been recently suggested that supermassive black holes at z approximate to 5-6 might form from superfast (M greater than or similar to 10(4) M-circle dot yr(-1)) accretion occurring in unstable, massive nuclear gas discs produced by mergers of Milky Way-sized galaxies. Interestingly, such a mechanism is claimed to work also for gas enriched to solar metallicity. These results are based on an idealized polytropic equation-of-state assumption, essentially preventing the gas from cooling. We show that under more realistic conditions, the disc rapidly (< 1 yr) cools, the accretion rate drops and the central core can grow only to approximate to 100 M-circle dot. In addition, most of the disc becomes gravitationally unstable in approximate to 100 yr, further quenching the accretion. We conclude that this scenario encounters a number of difficulties that possibly make it untenable.