A newly-discovered spiral galaxy, dubbed the Big Wheel, formed just 2 billion years after the big bang 鈥� far earlier, considering its size, than astronomers thought possible.
, at Swinburne University of Technology in Melbourne, Australia, says the discovery was an accident. He and his colleagues were looking for quasars, energetic regions at the heart of some galaxies, with the James Webb Space Telescope in November 2022 when a 鈥渓arge spiral galaxy popped up鈥�.
鈥淚t was a nice, beautiful spiral galaxy, but we didn鈥檛 really realise the significance of it at first,鈥� says Nanayakkara.
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However, after analysing the light from the galaxy to determine its redshift 鈥� a measure of how fast an object is moving away from us in space which is related to its distance from us and its age 鈥� the researchers discovered they were seeing the Big Wheel as it was just two billion years after the big bang.
More surprisingly, the galaxy is almost 98,000 light years across, just shy of the Milky Way鈥檚 diameter of 100,000 light years. The Big Wheel is also only one order of magnitude less massive than our galaxy, at one hundred billion solar masses rather than one trillion.
鈥淏ut you have to remember that the Milky Way has had another 10 billion years or so to grow than the Big Wheel,鈥� says Nanayakkara. While the newly-spied object isn鈥檛 the we know of, it is certainly the largest for its age 鈥� and it is now likely to be far larger than the Milky Way, as we are seeing it as it looked 10 to 12 billion years ago, he says.
Under our current understanding of the early universe, the development of such a large spiral galaxy this early on isn鈥檛 impossible, but it was thought unlikely, says Nanayakkara. He suggests that it may have been caused by multiple galaxies colliding and merging at a fast rate, or by cold gas from the universe accreting into the galaxy.
鈥淔inding one of these galaxies is not a problem for cosmological theories, because one could be an outlier, but if we keep finding more, then I think we may have to say 鈥極K, our models might need some refining鈥�,鈥� he says.
at the University of Sydney in Australia says the most important aspect of the discovery is that disc galaxies like our own Milky Way must have grown very quickly in the early universe.
鈥淭his galaxy, the Big Wheel, stretches this problem further, being a rather chunky disc galaxy, almost as large as our Milky Way today,鈥� says Lewis.
鈥淥ne big question remains: how rare are galaxies like the Big Wheel? We expect them to be quite rare, but if future observations throw up more examples, we will have to go back to the drawing board for our ideas of galaxy formation and evolution,鈥� he says.
Nature Astronomy
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