A Milky Way-like barred spiral galaxy at a redshift of 3

The majority of massive disk galaxies in the local Universe show a central stellar bar. Theory and simulations suggest bars develop in dynamically cold stellar disks at low redshift, with strong gas turbulence at high redshift suppressing or delaying bar formation, and predict bars to be rare beyond z ≈ 1.5 in Milky Way progenitors. Here we report ceers-2112, a barred spiral galaxy at photometric redshift z ≈ 3 that was already mature when the Universe was ~2 Gyr old. Its stellar mass (M* = 3.9 × 10^10 M⊙) and barred morphology indicate it is a plausible Milky Way progenitor in both structure and early mass assembly. From its properties we infer that baryons may have dominated over dark matter in galaxy centres at z = 3, high-redshift bars could form in ~400 Myr, and dynamically cold stellar disks could already be in place by z = 4–5.