Star Formation in the Early Universe
JPL / CalTech, Pasadena, US
|Stars and protostars accreting at sufficiently high rates are unable to thermally adjust and will bloat up to radii typical of protostars on the Hayashi track, irregardless of whether central hydrogen-burning has commenced. For Pop III star formation this means that very massive M ~ several 100 Msol or even supermassive M ~ 100,000 Msol stars can form without radiative feedback limiting the final mass. The metal-free accreting gas is virtually opacity-free to the cool radiation emitted by the ~5000 K stellar surface. The resulting final mass thus depends on how long accretion onto the star can be maintained at sufficiently high rates. If accretion occurs in episodic bursts, the critical average accretion rate that prevents a star from reaching main sequence radii can be lower than for slowly varying accretion. This effect is relevant for both Pop III star formation and present-day massive star formation.
|Caption: The evolution of the stellar interior structure for a primordial protostar accreting metal-free gas in 100-yr "bursts" at 1 Msol/yr alternating with more quiescent phases of dM/dt = 0.001 Msol/yr lasting 1080 yr. The black solid lines indicate the positions of the mass coordinates for 100% (stellar surface), 80%, 60%, 40% and 20% of the total stellar mass. The yellow (white) regions denote convective (radiative) layers with no nuclear burning. The brown (green) regions show radiative deuterium-burning (convective hydrogen-burning) layers. The pink regions are deuterium-burning convection zones.
Y. Sakurai, U Tokyo, JP
T. Hosokawa, U Tokyo, JP
N. Yoshida, U Tokyo, JP
Suggested Session: Massive Star Formation