The authors consider the quasi-static contraction of primordial stars composed of pure hydrogen and helium gas. They follow numerically the evolution of a star of mass M* = 5 M_sun; from the end of protostellar accretion to the onset of hydrogen burning. Although the protostellar core of this mass is radiatively stable and undergoing nonhomologous contraction, its large surface area and luminosity force the star to a partially convective, homologously contracting state within only 100 yr. The star follows a conventional pre-main-sequence track in the H-R diagram, reaching the zero-age main sequence after 1.2×10⁶yr, with a luminosity of 880 L_sun; and a radius of 1.2 R_sun;. All stars with M* < 7 M_sun; undergo a similar rapid relaxation to homologous contraction because of their large initial radii and surface luminosities.
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Stahler et al. (1986) studied this question.