The onset of star formation 250 million years after the Big Bang

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A fundamental quest of modern astronomy is to locate the earliest galaxies and study how they influenced the intergalactic medium a few hundred million years after the Big Bang.

• The abundance of star-forming galaxies is known to decline from redshifts of about 6 to 10, but a key question is the extent of star formation at even earlier times, corresponding to the period when the first galaxies might have emerged.
• Here we present spectroscopic observations of MACS1149-JD1, a gravitationally lensed galaxy observed when the Universe was less than four per cent of its present age.
• We detect an emission line of doubly ionized oxygen at a redshift of $9.1096\pm0.0006$, with an uncertainty of one standard deviation.