The cosmic dawn ended 200 million years later than cosmologists thought

Artist’s impression of a bright quasar – IgorZh /

Using light from dozens of distant quasars, astronomers have determined that the cosmic dawn, during which the first stars began to form, ended much later than expected.

67 quasars analyzed

For a period of about 100 million years, beginning about 380,000 years after Big Bang, the cosmos was largely shrouded in darkness. Stars and galaxies then began to form, emitting light and ionizing intergalactic hydrogen gases in a process called reionization, or cosmic dawn.

As part of the work published in the journal Monthly Bulletins of the Royal Astronomical Society, Sarah Bosmann and his colleagues from theMax Planck Institute were able to pinpoint when this phase ended using light from 67 quasars, extremely bright objects powered by supermassive black holes. Far enough away for scientists to be sure they formed in the billions of years since Big Bangthese were observed with the Very large telescope to Chile and the observatory WM Keck at Hawaii.

As the light traveled from the quasars towards Earthdifferent wavelengths were absorbed by hydrogen in its ionized and non-ionized forms. Taking into account the constant expansion ofuniverseGerman scientists analyzed the dark absorption lines in the light spectrum to determine when it stopped passing through unionized hydrogen and began encountering only ionized hydrogen in intergalactic space.

Galaxy in Space – Outer Space /

A phase that ended 1.1 billion years after the Big Bang

During reionization, galaxies emit gigantic bubble-like structures “, To explain Bosman. ” It is generally assumed that such a process ends when the latter merge and the hydrogen is evenly ionized around all quasars. »

This approach allowed the team to determine that the cosmic dawn was 1.1 billion years after Big Bang, 200 million years later than predicted by previous models. This implies that the first generation of stars and galaxies are closer to the origin of reionization, and therefore easier to observe, than cosmologists thought.

Since the Big Bang, the universe has gone through many phases that we are only just beginning to track “, estimated Bosman. “ The next step will be to go even further back in time and link the reionization data to the galaxies behind the process, so we can actually see the galaxies destroying the gas. »

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