RAPIDLY ACCRETING SUPERGIANT PROTOSTARS: EMBRYOS OF SUPERMASSIVE BLACK HOLES?

Direct collapse of super-massive stars (SMSs) is a possible pathway for generating super-massive black holes in the early universe. It is expected that an SMS could form via very rapid-mass accretion with M ~ 0.1-1 M sub([middot in circle]) yr[sup -1] during the gravitational collapse of an atomic-cooling primordial gas cloud. In this paper, we study how stars would evolve under such extreme rapid mass accretion, focusing on the early evolution until the stellar mass reaches 10[sup 3] M sub([middot in circle]). To this end, we numerically calculate the detailed interior structure of accreting stars with primordial element abundances. Such "super-giant" protostars have effective temperatures as low as T[subeff] [Asymptotically = to] 5000 K throughout their evolution and because they hardly emit ionizing photons, they do not create an H II region or significantly heat their immediate surroundings. Thus, radiative feedback is unable to hinder the growth of rapidly accreting stars to masses in excess of 10[sup 3]M sub([middot in circle]) as long as material is accreted at rates M[lowast][> or ~] 10[sup-2 ]M sub([middot in circle]) yr[sup -1].