A galaxy seen 700 million years after the big bang appears surprisingly mature, suggesting some pockets of the early universe were more tranquil than expected
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| JWST’s view of the galaxy JADES-GS+53.18343-27.79097 NASA, ESA, CSA, JADES Collaboration |
Astronomers using the James Webb Space Telescope (JWST) have found a galaxy in the early universe that appears surprisingly mature, having grown a substantial inner core much more quickly than expected.
The galaxy was found by a JWST survey called JADES, and we see it as it was 700 million years after the big bang, when it was perhaps just 100 million years old. It has a mass about 150 times less than that of the Milky Way.
It had been thought that galaxy formation was fairly tumultuous in the more-crowded early universe, with protogalaxies crashing together and merging or galaxies rapidly collapsing. But this galaxy seems to be growing in a more sedate manner typical of those in the later universe, with a central core and a surrounding star-forming disc.
Probing how galaxies grew in the early universe, in a period of time known as the Epoch of Reionisation that lasted from 400 million to a billion years after the big bang, hasn’t been possible until now. “We haven’t had good enough imaging,” says William Baker at the University of Cambridge, who led the study. JWST has changed that, finding more distant galaxies than we have seen before, and hence existing sooner after the big bang.
This one, named JADES-GS+53.18343-27.79097, is small – barely 1500 light years across, which is some 70 times smaller than the Milky Way. “It’s pretty compact,” says Baker. But its central core is comparable in mass with the cores of modern galaxies, while its outer disc is growing in size at a rate of about eight stars per year, with the galaxy expected to reach full size in about 3 billion years.
Christopher Conselice at the University of Manchester, UK, says the discovery suggests galactic structure settled down “earlier than we may have anticipated” in the early universe. “To have something that’s so mature and forming in a way we think galaxies form billions of years later is quite unique,” he says.
That could point to an early universe that was less tumultuous than expected. “Whilst the majority of the universe was probably very violent at this epoch, with mergers and very rapid assembly, I think this shows that there are pockets of the universe where things are calmer than other areas,” says Conselice. “It’s also showing us that galaxy formation is happening much quicker than we thought.”
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