For two years, an international team has been studying what astronomers call the Cosmic Dawn: the period in the first few hundred million years after the Big Bang when the first galaxies were born.
Using NASA’s James Webb Space Telescope (JWST), they have now discovered two of the earliest and most distant galaxies confirmed to date.
These galaxies date back just 300 million years after the Big Bang and mark an important milestone in the study of the early universe, according to astronomer Brant Robertson of the University of California-Santa Cruz, who co-led the team working in JADES (the JWST ) worked. Advanced deep extragalactic research).
“This discovery is completely unexpected and will likely be regarded as the most significant extragalactic discovery with JWST to date,” said Robertson, a professor of astronomy and astrophysics who serves on the JADES Steering Committee. He is the lead author of the first of three papers reporting various aspects of the discovery.
In one paper, the authors concluded: “With high-redshift galaxy populations now forming less than 300 million years after the Big Bang, we have increased our reach into the cosmic past by 40% during the first eighteen months of JWST operations.”
‘Redshift’ refers to an effect caused by the expansion of the universe, where the wavelength of light from distant galaxies stretches as it travels. In these newly discovered galaxies, the effect is extreme, stretching them by a factor of 15 and even shifting the galaxies’ ultraviolet light into infrared wavelengths where only JWST can see it.
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In search of early galaxies
Modern theory holds that galaxies form in special regions where gravity has concentrated cosmic gas and dark matter into dense clumps known as “halos.” These halos evolve rapidly in the early universe, merging into ever-larger collections of matter. This rapid development is why astronomers are so eager to find even earlier galaxies: each small step moves our gaze toward a less evolved period, where brighter galaxies are even more conspicuous and unusual.
“This galaxy is a real gem and points to even more hidden treasures in the early Universe,” said Professor Robertson.
Found in a region near the Hubble Ultra Deep Field, the new galaxies, which have been spectroscopically confirmed, are now known as JADES-GS-z14-0 (the more distant galaxy) and JADES-GS-z14-1.
According to NASA, the JADES-GS-z14-0 is not only the new distance record holder, but also remarkable for its size and brightness. JWST measures the galaxy with a diameter of more than 1,600 light-years. Many of the brightest galaxies produce most of their light through gas falling into a supermassive black hole, creating a quasar. But the team says the large size of JADES-GS-z14-0 means its light must be produced by young stars.
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Deeply hidden gems
And yet the massive galaxy was a mystery to the JADES team when they first saw it over a year ago, because it appears so close to a foreground galaxy in the sky that they couldn’t be sure the two weren’t were neighbors. But in October 2023, the JADES team performed even deeper imaging – five full days with the JWST near-infrared camera on just one field – to form the ‘JADES Origins Field’. Using filters designed to better isolate early galaxies, confidence grew that JADES-GS-z14-0 was very far away indeed.
Furthermore, the galaxy happened to fall in an area where the team had performed ultra-deep imaging with the JWST Mid-InfraRed Instrument. These combined imaging results convinced the team to include the galaxy in what was planned as the final observation of JADES, a 75-hour campaign to perform spectroscopy on faint early galaxies. The spectroscopy confirmed their hopes that JADES-GS-z14-0 was indeed a record-breaking galaxy – and that the fainter candidate, JADES-GS-z14-1, was almost as distant.
The combination of its high brightness and stellar origin makes JADES-GS-z14-0 the most striking evidence yet for the rapid formation of large, massive galaxies in the early Universe.
“We could have detected this galaxy even though it was ten times fainter, meaning we could have seen other examples even earlier in the universe – probably within the first 200 million years,” Robertson added.
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Robertson’s article of May 30, Earliest galaxies in the JADES Origins field: Luminosity function and cosmic star formation rate density 300 Myr after the Big Banghas been accepted for publication in the Astrophysical Journal.
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