Washington: Since beginning operations last year, the James Webb Space Telescope has provided a stunning glimpse of the early history of our universe, observing a collection of galaxies belonging to a mysterious era called the cosmic dawn.
But the existence of massive and mature galaxies during the early stages of the universe defied expectations – too big and too soon. This left scientists scrambling for explanations, questioning the fundamentals of cosmology, the science of the origin and evolution of the universe. A new study may solve the mystery without tearing up the textbooks.
The researchers used sophisticated computer simulations to model how early galaxies evolved. These indicate that in the first few hundred million years after the Big Bang that initiated the universe 13.8 billion years ago, star formation in these galaxies occurred differently than in the larger galaxies like our Milky Way that populate the universe today.
They found that star formation in early galaxies occurred in large, occasional bursts rather than at a steady pace. This is important because scientists typically use a galaxy’s brightness to measure how big it is – the collective mass of its millions or billions of stars.
So, according to the study, these galaxies may be relatively small as expected, but just as bright as truly massive galaxies due to spectacular bursts of star formation – giving the illusion of larger mass.
“Astronomers can safely measure how bright those early galaxies are because photons (particles of light) are directly detectable and countable, whereas it is very difficult to tell whether those galaxies are actually that big or massive. “They appear because they are observed to be bright,” said Guochao Sun, a postdoctoral fellow in astronomy at Northwestern University in Illinois and lead author of the study published this week in Astrophysical Journal Letters.
Webb, which was launched in 2021 and becomes operational in 2022, detected galaxies about 10 times brighter than predicted based on most theoretical models.
“According to the standard model of cosmology, there should not have been very many massive galaxies during the cosmic dawn because galaxies took time to evolve after the Big Bang. Immediately after the Big Bang, the universe was filled with very hot, almost uniform plasma – a ball of fire – and there were no stars or galaxies,” said Claude-André Foucher-Giguere, an astronomer at Northwestern University and senior author of the study.
“In our new paper, we use our simulations to quantitatively show that bursts of star formation produce flashes of light that can explain the very bright galaxies observed by Webb. And the reason it’s so important is that “That’s how we explain these very bright galaxies without having to break the standard cosmological model,” said Foucher-Giguere.
The simulations in the study were conducted as part of the Feedbacks on Relativistic Environments (FIRE) research project. The findings focused on a phenomenon called “exploding star formation.”
“In contrast to star formation at a nearly constant rate, star formation activity in those early galaxies occurred intermittently, sometimes intermittently, with some large fluctuations over time. This, in turn, caused large changes in them That’s because the light seen by telescopes like JWST was emitted by young stars forming in those galaxies,” Sun said.
Researchers have an idea why this phenomenon occurs in small galaxies. In these, a cluster of very massive stars may form in a sudden explosion, then explode as a supernova after a few million years due to their enormous size. They blast gas into space which becomes the material for another burst of star formation. However, strong gravitational effects in larger galaxies prevent these explosions, allowing stable star formation.
Sun hopes that the web will continue to challenge our understanding of the universe and provide new insights, whether or not it meets scientific expectations.
“That’s exactly how science developed and moved forward,” Sun said.