Scientists untangle mystery about the universe's earliest galaxies

The existence of massive and mature galaxies during the universe’s infancy defied expectations and baffled scientists. It left them scrambling for an explanation while questioning the basic tenets of cosmology

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 existence of what appear to be massive and mature galaxies during the universe's infancy defied expectations - too big and too soon. That left scientists scrambling for an explanation while questioning the basic tenets of cosmology, the science of the origin and development of the universe. A new study may resolve the mystery without ripping up the textbooks.

The researchers used sophisticated computer simulations to model how the earliest galaxies evolved. 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.

Star formation in the early galaxies occurred in occasional big bursts, they found, rather than at a steady pace. 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.

Also Read | Billion-light-year-wide ‘bubble of galaxies’ discovered

So, according to the study, these galaxies may have been relatively small, as expected, but might glow just as brightly as genuinely massive galaxies do - giving a deceptive impression of great mass - because of brilliant bursts of 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.