A population of red candidate massive galaxies ~600 Myr after the Big Bang.

Galaxies with stellar masses as high as roughly 10 solar masses have been identified out to redshifts z of roughly 6, around 1 billion years after the Big Bang. It has been difficult to find massive galaxies at even earlier times, as the Balmer break region, which is needed for accurate mass estimates, is redshifted to wavelengths beyond 2.5 μm. Here we make use of the 1-5 μm coverage of the James Webb Space Telescope early release observations to search for intrinsically red galaxies in the first roughly 750 million years of cosmic history. In the survey area, we find six candidate massive galaxies (stellar mass more than 10 solar masses) at 7.4 ≤ z ≤ 9.1, 500-700 Myr after the Big Bang, including one galaxy with a possible stellar mass of roughly 10 solar masses. If verified with spectroscopy, the stellar mass density in massive galaxies would be much higher than anticipated from previous studies on the basis of rest-frame ultraviolet-selected samples.