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WASHINGTON, Oct 6 – Since beginning operations last year, the James Webb Space Telescope has provided an astonishing glimpse of the early history of our universe, spotting a collection of galaxies dating to the enigmatic epoch called cosmic dawn.
But, the presence of massive and mature galaxies at the dawn of the universe defied expectation – they were too large and too early. Scientists were left scrambling to find an answer, while also questioning the fundamental tenets in cosmology – the science that studies the origin and evolution of the universe. New research may solve the mystery, without having to rip up textbooks.
The scientists used computer simulations in order to model the evolution of galaxies. These indicated that star formation unfolded differently in these galaxies in the first few hundred million years after the Big Bang event 13. 8 billion years ago that initiated the universe than it does in large galaxies like our Milky Way populating the cosmos today.
They found that star formation occurred at an irregular pace in early galaxies rather than in steady bursts. That is important because scientists typically use a galaxy’s brightness to gauge how big it is – the collective mass of its millions or billions of stars.
According to this study, the galaxies were likely smaller than expected but could have glowed as brightly, giving an impression of massive mass, because they had experienced brilliant bursts in star formation.
“Astronomers can securely measure how bright those early galaxies are because photons (particles of light) are directly detectable and countable, whereas it is much more difficult to tell whether those galaxies are really big or massive. They appear to be big 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 the Astrophysical Journal Letters.
Webb, which was launched in 2021 and became operational in 2022, detected about 10 times more very bright galaxies from cosmic dawn than anticipated based on most theoretical models.
“According to the standard model of cosmology, there should not be many very massive galaxies during cosmic dawn because it takes time for galaxies to grow after the Big Bang. Claude-Andre Faucher Giguere, senior author of the study and an astrophysicist at Northwestern University, said that the universe immediately after the Big Bang was filled with a hot and uniform plasma – a “fireball” – and no galaxies or stars were visible.
” In our new article, we demonstrate quantitatively that bursts in star formation can produce flashes or light which could explain the bright galaxies seen by Webb. Faucher Giguere said that this was significant because it allowed us to explain the very bright galaxies observed by Webb without breaking the standard cosmological models.
The simulations in the study were conducted as part of the Feedback of Relativistic Environments (FIRE) research project.
The findings centered upon a phenomenon called “bursty star formation.”
“In contrast to forming stars at a nearly constant rate, the star formation activity in those early galaxies went on-and-off, on-and-off, with some large fluctuations over time. This, in turn, drives large variations in their brightness because the light seen by telescopes like JWST was emitted by the young stars formed in those galaxies,” Sun said.
The researchers have an idea of why this phenomenon occurs in smaller galaxies. In these, a batch of very large stars may form in a sudden burst, then explode as supernovas after just a few million years due to their great size. They blast gas into space that becomes ingredients for another burst of star formation. The stronger gravitational forces in large galaxies stop these explosions and favor steady star formation.
Sun believes that Webb will continue to provide new insights and challenge our current understanding of the cosmos, whether or not it is able to meet scientific expectations.
“This is exactly how science is done and progressed,” Sun said.
Reporting by Will Dunham, Editing by Rosalba O’Brien
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