In low-metallicity environments, massive stars are more easily formed than in the solar neighborhood. In this article, we see the following examples of low-mass star formation. We first describe the first star formation in the universe and argue that they are typically ordinary-sized massive stars, rather than very massive (> 100M⊙) ones. Next, we see how the metal-enrichment changes the thermal evolution of gas, thereby causing the shift of characteristic stellar mass towards lower mass. Finally, we discuss the possibility of forming supermassive stars in some special conditions in young galaxies.

The effect of variations of the fundamental constants on the thermonuclear rate of the triple alpha reaction, 4He(αα,γ)12C, that bridges the gap between 4He and 12C is investigated. We follow the evolution of 15 and 60 M⊙ zero metallicity star models, up to the end of core helium burning. They are assumed to be representative of the first, Population III stars undergoing a very peculiar evolution due to the absence of initial CNO elements (zero metallicity). The calculated oxygen and carbon abundances resulting from helium burning can then be used to constrain the variations of the fundamental constants.