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The crack is inward. Cosmology was going to take some time to appear. But when the James Webb Space Telescope (JWST) opened its lens last spring, the most distant and brightest galaxies immediately entered the telescope’s view. “They were very stupidly bright, and they stood out,” said Rohan Naidu, an astronomer at the Massachusetts Institute of Technology.
The observed distance of the galaxies from Earth suggests that they formed much earlier in the history of the universe than anyone had imagined. (If it’s far away, it’s been glowing for a long time.) Doubts swirled, but in December, astronomers confirmed that some galaxies are indeed far away, and as primordial, as they seem. The first of those confirmed galaxies burst into light 330 million years after the Big Bang, making it the new record holder for the best-known structure in the universe. That galaxy was very faint, but other candidates that coincided around the same time were already glowing brightly, meaning they could be close to each other.
How did the stars ignite in the superheated gas cloud after the Big Bang? How could they hastily entangle themselves in massive structures bound to gravity? Finding such large, bright, early galaxies seems akin to finding a fossil rabbit in Precambrian strata. “There are no big things in the early days. It takes time to get big,” says Mike Bolan-Colchin, a theoretical physicist at the University of Texas at Austin.
Astronomers are beginning to wonder if the abundance of early massive objects will challenge our current understanding of the cosmos. Some researchers and the media have argued that the telescope’s observations are violating the standard model of cosmology—the well-tested Lambda Cold Dark Matter, or ΛCDM, model—and suggest exciting new cosmic elements or governing laws. Since then, it has become clear that the ΛCDM model is resistant. Rather than forcing researchers to rewrite the laws of cosmology, JWST’s discoveries have made astronomers rethink how galaxies form, especially in the cosmic beginning. The telescope has not yet cracked cosmology, but this does not mean that the matter of very early galaxies will be anything but ages.
Simple times
It helps to understand what cosmologists know, or think they know, about the universe to see why the discovery of very early and bright galaxies is so surprising.
After the Big Bang, the baby universe began to cool. Within a few million years, the swirling plasma that filled space cooled, and the electrons, protons, and neutrons decayed into atoms, mostly neutral hydrogen. Things were quiet and dark for an unknown amount of time known as the dark ages of the universe. Then something happened.
Most of the matter that flew after the Big Bang was made of something we can’t see, dark matter. It had a powerful effect on the cosmos, especially at first. In the standard picture, cold dark matter (meaning invisible, slow-moving particles) is thrown indiscriminately about the cosmos. In some areas the distribution is denser and in these regions it starts to break down. Visible matter, atoms, are clustered around dark matter. As the atoms cooled, they eventually clumped together, and the first stars were born. These new sources of radiation filled the universe with neutral hydrogen during the so-called reionization era. Under gravity, large and complex structures grew, forming a vast cosmic web of galaxies.
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