by Shortly after the James Webb Space Telescope (JWST) began its science operations, astronomers announced that they had discovered galaxies in the early universe that were far too big, bright and full of stars for their age. . While headlines around the world claimed that these galaxies were “shattering” our understanding of the Big Bang, the truth is much more nuanced – and much more interesting.
The Big Bang theory is our general picture of the history of the universe, starting in the deep past, when the cosmos was much smaller, hotter and denser than it is today. This model, originally developed in the early 20th century, has survived a battery of observational tests and is exceptionally good at explaining a variety of cosmological observations, including the transfer of light from galaxies far away, the appearance of radiation left in the form of cosmic. microwave background, abundance of light elements, and evolution of galaxies and larger structures.
Although the Big Bang theory cannot say which galaxies will appear where, it can talk about probabilities. For example, cosmologists can say roughly how many small galaxies, how many medium-sized galaxies and how many large galaxies should appear 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 expressly designed to study.
In 2022, astronomers announced that they had discovered extremely distant galaxies that were surprisingly, very strange. They had a measure of the redshift of the galaxies to be over 16, which suggests that these galaxies existed just 200 million to 250 million years after the Big Bang. But they were huge and seemed to be fully formed, with spiral arms and everything.
Related: No, the Big Bang theory is not ‘broken.’ This is how we know.
The appearance of these galaxies was far outside the expectations of the Big Bang theory; they were like meeting teenagers in a kindergarten classroom. So what was going on?
Bending cosmology
Look at the brazen headlines announcing the death of the Big Bang theory. But those stories left out a crucial detail: astronomers estimated the change in those galaxies through a technique called photometry, which is extremely uncertain. A full evaluation of the ability of these galaxies to “break” cosmology would have to await a more precise measurement of their redshift, and therefore their age.
When those more accurate measurements finally arrived a few months later, those galaxies changed from record breakers to … ordinary stars. For example, the redshift of one galaxy was revised from more than 16 years old to just 4.9, moving its age from 240 million years after the Big Bang to more than a billion years. That’s more than enough time for the usual Big Bang theory to explain their sizes and shapes.
But along with the less exciting revisions came several new 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 cosmos was only 290 million years old.
Astronomers fully expected galaxies to exist 290 million years after the Big Bang; that’s why they built JWST. And as galaxies go, JADES-GS-z14-0 is certainly a youngster – 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 break the cosmology, but enough to open some questions about the origin and development of the first visible galaxies in the universe.
Construction cosmology
It is quite possible that the Big Bang theory is wrong; scientists must maintain the mental discipline to admit the possibility. But with such a wealth of evidence behind it, it is unlikely that the Big Bang will be without sitting from one observation. And it’s worth reiterating that JWST is doing exactly what we designed and built it for: answer some big long questions about how the first stars and galaxies appeared.
It is entirely possible that cosmologists will be able to explain the appearance of galaxies like JADES-GS-z14-0 within the framework of the Big Bang without making any major revisions. For example, big black holes they may have appeared before these galaxies formed, and their super-powerful gravitational pull may have triggered bright bursts of star formation. Or maybe supernova feedback and other mechanisms caused the first galaxies to be richer in stars than today’s galaxies, making the early galaxies appear mighty despite their small size.
Related stories:
— The James Webb Space Telescope never disproved the Big Bang. This is how that lie was spread.
— Early galaxy images from the James Webb Space Telescope were extremely bright. Now we know why.
— The James Webb Space Telescope sees early galaxies defying the ‘cosmic rule book’ of star formation
Or perhaps our initial observations are biased towards these small but bright outliers and further campaigns will reveal larger populations of more accurate galaxies, reducing the tension with galaxy formation models.
And finally, we may need to add some new ingredient to the universe, such as allowing dark energy to evolve over time, to produce these types of galaxies so early.
This is exciting enough on its own, without the need to invoke the Big Bang as we know it. There are more than enough mysteries and hidden corners within the universe to keep astronomers up at night thinking about the possibilities – and up in the morning to continue working on how to solve them.
