A distant galaxy could open up a new era of cosmic history, suggesting that the first stars formed earlier than previously thought.
Galaxy MACS1149-JD1 is 13.28 billion light years away and contains the most distant detection of oxygen, which could indicate stars which have already completed their life cycle.
The galaxy's stars are believed to have formed 250 million years after the birth of the universe, earlier than any others known.
The faint light of the galaxy has taken so long to reach Earth that its journey began just 500 million years after the Big Bang.
Dr Nicolas Laporte, from University College London, who co-led the team, said: "This is an exciting discovery as this galaxy is seen at a time when the Universe was only 500 million years old and yet it already has a population of mature stars.
"We are therefore able to use this galaxy to probe into an earlier, completely uncharted, period of cosmic history."
A team of British-led astronomers used an Atacama Large Millimetre/Submillimetre Array (Alma), a radio telescope, and the European Southern Observatory's Very Large Telescope (VLT), both in Chile's Atacama desert, to study the galaxy.
The "cosmic dawn" refers to the mysterious period in which the first galaxies emerged from total darkness.
Co-author Professor Richard Ellis, also from UCL, said: "Determining when cosmic dawn occurred is akin to the Holy Grail of cosmology and galaxy formation.
"With MACS1149-JD1, we have managed to probe history beyond the limits of when we can actually detect galaxies with current facilities.
"There is renewed optimism we are getting closer and closer to witnessing directly the birth of starlight.
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"Since we are all made of processed stellar material, this is really finding our own origins."
The findings appear in the latest issue of Nature journal.