Why was the Webb Telescope Galaxy so mysteriously bright?
Artistic depiction of early stellar galaxies. Stars and galaxies appear as bright white points of light, while dark matter and more diffuse gases appear in purple and red.
(Aaron M. Geller, Northwestern, CIERA+IT-RCDS/via EurekAlert)
In 2022, when the James Webb Space Telescope (JWST) began beaming its cosmic snapshots home, all of humanity marveled at never-before-seen images of ancient galaxies from the comic dawn. These images date back as much as a billion years, to a mere 500 million years after the Big Bang, when the first stars, galaxies and black holes were about to form from cosmic dust.
When this early data about the galaxy first arrived, astronomers were scratching their heads. Aside from their attractive charm, they were also a scientific mystery! It was puzzling to see that these galaxies, which formed as early as 500 million years after the Big Bang, appear to be giant, mature objects today, comparable to our own Milky Way.
Now, a new study conducted by a team of famous astrophysicists from various American universities has tried to solve this mystery!
Redemption for the standard model
The galaxies captured by the James Webb Space Telescope were too young to appear huge, bright and mature, considering their formative period – our universe was just an infant at this point. These observations have led many physicists to question the standard model of cosmology, which predicts how galaxies start out small after the Big Bang and then grow into giants driven by mergers and collisions in the universe.
“The discovery of these galaxies was a big surprise because they were much brighter than expected,” said study senior author Claude-Andre Foucher-Gière of Northwestern University.
Based on supercomputer simulations, the new study shows that we may not need to worry about updating the standard model of cosmology right away. Turns out, these galaxies may not be very massive, and instead could be unusually bright!
“Normally a galaxy is bright because it is large. But because these galaxies formed at cosmic dawn, not enough time has passed since the Big Bang. How could these massive galaxies assemble so quickly? Our simulations show that galaxies have no problem forming this brightness with Cosmic dawn.
Explosive star formation
The new theory suggests that less massive galaxies could glow just as brightly thanks to sudden, brilliant bursts of star formation, after years of dormancy. This phenomenon, called “explosive star formation,” is in stark contrast to how stars form in the universe today.
In massive galaxies like the Milky Way, stars form at a constant pace, with the number of stars gradually increasing over time. But in the “explosive star formation” phase, stars form in an alternating pattern — many stars at once, followed by millions of years of quiescence with very few new stars and then a bright flash after eons of dormancy.
So, perhaps, in the Webb Telescope observations, the galaxies appeared so bright and massive because we were viewing them during these living starbursts, and they didn’t contain as many stars as today’s galaxies.
The validity of these simulations can only be confirmed after astronomers take more precise readings of these mysterious galaxies at cosmic dawn. But for now, the Standard Model of cosmology appears to have survived.
The study was published in Astrophysical Journal Letters It can be accessed here.
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