First Star Formation in the Presence of Primordial Magnetic Fields

Abstract

It has been recently claimed that primordial magnetic fields could relieve the cosmological Hubble tension. We consider the impact of such fields on the formation of the first cosmological objects, mini-halos forming stars, for present-day field strengths in the range of $2\times 10^{-12}$ - $2\times 10^{-10}$ G. These values correspond to initial ratios of Alvén velocity to the speed of sound of $v_a/c_s\approx 0.03-3$. We find that when $v_a/c_s\ll 1$, the effects are modest. However, when $v_a\sim c_s$, the starting time of the gravitational collapse is delayed and the duration extended as much as by $\Delta$z = 2.5 in redshift. When $v_a>c_s$, the collapse is completely suppressed and the mini-halos continue to grow and are unlikely to collapse until reaching the atomic cooling limit. Employing current observational limits on primordial magnetic fields we conclude that inflationary produced primordial magnetic fields could have a significant impact on first star formation, whereas post-inflationary produced fields do not.

8 pages, 6 figures, submitted to ApJL

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• Evolution of primordial magnetic fields during large-scale structure formation
• The Pandora project. I: the impact of radiation and cosmic rays on baryonic and dark matter properties of dwarf galaxies
• Exponentially amplified magnetic field eliminates disk fragmentation around the Population III protostar
• Impact of magnetic fields on Population III star formation
• Primordial magnetic fields: consistent initial conditions and impact on high-z structures
• Revisiting primordial magnetic fields through 21-cm physics: Bounds and forecasts