However, it is not clear whether there was a magnetic field in the interstellar medium in the early universe.

Finally, because the first stars were also created in binaries and multiple systems, they could be subjected to mass-exchange, mass loss from their systems and enhancement of their winds by tidal forces from companion stars as it is theoretically well understood and observationally confirmed for the present generations of stars.

Motivated by these studies we explore a scenario for the evolution of very massive and low-metallicity Population III mass losing stars.

Evolutionary Models at Low Metallicity {#results}
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Input physics and initial conditions
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In agreement with [@Castellani2000] we take as the Population III stars all the stellar objects with metallicity below a not yet well defined upper limit between $Z=10^{-10}$ and $10^{-6}$. Depending on their metallicity we distinguish between galactic and pregalactic stars, the former with metallicity $Z=10^{-6}$, and the later with $Z=10^{-9}$, both considered as lower metallicity stars, but not zero-metallicity stars.

The concept of critical metallicity has been used to characterize the transition between Population III and Population II star formation modes [@Omukai2001; @Bromm2001; @Schneider2002; @Schneider2003; @Mackey2003; @Bromm2004].

Our evolutionary models for both galactic and pregalactic Population III 