Shortly after the James Webb Space Telescope (JWST) began its scientific operations, astronomers announced that they had discovered galaxies in the early universe that were very large, bright, and full of stars for their age. While headlines around the world claimed that these galaxies “broke” our understanding of the Big Bang, the truth is much more nuanced and much more interesting.
The Big Bang theory is our overall picture of the history of the universe, starting from the deep past of the universe and extending back to a time when the cosmos was much smaller, hotter, and denser than it is today. First developed in the early 20th century, this model has survived a number of observational tests and is extremely good at explaining a variety of cosmological observations, including the redshift of light from distant galaxies, the appearance of residual radiation in the form of the cosmic microwave background, the abundance of light elements, and the evolution of galaxies and larger structures.
While the Big Bang theory can’t say for sure which galaxies will appear where, it can tell us about the possibilities. For example, cosmologists can tell us approximately how many small galaxies, how many medium-sized galaxies, and how many large galaxies should have appeared in a given volume at a given age of the universe. But until JWST, we didn’t have direct observational access to the earliest stages of galactic evolution—something the telescope was explicitly designed to study.
In 2022, astronomers announced that they had found extremely distant galaxies that were surprisingly, oddly large. redshift The number of galaxies is more than 16, these galaxies It existed only 200 million to 250 million years after the Big BangBut they were still huge and appeared to be fully formed, with spiral arms and all.
Relating to: No, the Big Bang theory has not ‘collapsed.’ Let us explain how we know this.
These galaxies were so far outside the expectations of the Big Bang theory that they were like finding teenagers in a kindergarten classroom. So what was going on?
Twisted cosmology
The brazen headlines that declared the death of the Big Bang theory. But these stories left out one important detail: Astronomers estimated the redshift of these galaxies using a technique known as photometry, which is incredibly imprecise. A full assessment of these galaxies’ ability to “break” cosmology will have to wait for a more precise measurement of their redshifts, and therefore their ages.
When these more precise measurements finally came in a few months later, these galaxies had gone from record-breaking to just… normal galaxies. For example, one galaxy’s redshift was revised from 16 to just 4.9, and it had moved from 240 million years after the Big Bang to well over a billion years. That’s more than enough time for the normal Big Bang theory to explain their size and shape.
But along with these less exciting revisions came some newly confirmed redshifts of other galaxies, including JADES-GS-z14-0, the most distant galaxy currently known, with a redshift of 14.32. This galaxy was alive and well when the universe was just 290 million years old.
Astronomers fully expected galaxies to exist 290 million years after the Big Bang, which is why they built JWST. And as galaxies go, JADES-GS-z14-0 is certainly a young galaxy — just 1,600 light-years across, compared to the Milky Way’s 100,000 light-years. But interestingly, the galaxy is quite bright and full of stars — not enough to completely shatter cosmology, but enough to raise some questions about the origins and evolution of the first galaxies to appear in the universe.
Building cosmology
It’s entirely possible that the Big Bang theory is wrong; scientists must maintain the mental discipline to accept that possibility. But with so much evidence behind it, it’s unlikely that the Big Bang can be ruled out with a single observation. And it’s worth reiterating that JWST does exactly what we designed and built it to do: answer some important, ongoing questions about how the first stars and galaxies came into being.
It is entirely possible that cosmologists could explain the appearance of galaxies like JADES-GS-z14-0 in the Big Bang framework without making any major revisions. For example, Black holes may have formed before these galaxies, and their super-strong gravity may have triggered bright bursts of star formation. Or maybe supernova Feedback and other mechanisms caused the first galaxies to have more stars than today’s galaxies, making these early galaxies appear massive despite their small size.
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— James Webb Space Telescope sees early galaxies defy ‘cosmic rulebook’ of star formation
Or perhaps our early observations are biased toward these small but bright outliers, and later studies will reveal larger populations of more ordinary galaxies, thus reducing the tension with models of galaxy formation.
And finally, perhaps we need to add a new ingredient to the universe, for example, allowing dark energy to evolve over time to produce such galaxies at such early times.
That’s exciting enough on its own, without having to overturn the Big Bang as we know it. There are enough mysteries and hidden corners of the universe to keep astronomers awake at night wondering about the possibilities, and in the morning working on how to figure them out.