‘Bursty star formations’ could be secret behind cosmic dawn question

As the James Webb Space Telescope hurtles through space, it enables Earthbound researchers to look backward in time and study images of planets and galaxies as they looked billions of years ago. Bright and seemingly massive young galaxies glow in the blackness of space, providing a snapshot of a period known as the cosmic dawn.

There’s just one problem: The Webb images don’t match scientists’ models of how the universe formed.

But it might not be time to dump the standard model of cosmology yet. A recent analysis in the Astrophysical Journal Letters suggests an explanation for the surprisingly massive-seeming galaxies: brilliant, extremely bright bursts of newborn stars.

The galaxies photographed by the telescope looked far too mature and large to have formed so fully so soon after the universe began, raising questions about scientists’ assumptions of galaxy formation. But when researchers ran a variety of computer simulations of the universe’s earliest days, they discovered the galaxies probably are not as large as they seem.

Instead, they attribute their brightness to a phenomenon called “bursty star formation.” As clouds of dust and debris collapse, they form dense, high-temperature cores and become stars. Bursty galaxies spit out new stars in intermittent, bright bursts instead of creating stars more consistently. Usually, these galaxies are low in mass and take long breaks between starbursts.

Because the galaxies in question look so bright in photos produced by the Webb telescope, scientists at first thought they were older and more massive. But bursty systems with the ability to produce extremely bright, abundant light may appear more massive than they really are.

“A system doesn’t need to be that massive” to make really bright stars, Guochao Sun, a PhD candidate at Caltech who led the research, said in a news release. “If star formation happens in bursts, it will emit flashes of light. That is why we see several very bright galaxies.”

The simulations revealed that the cosmic dawn could have produced the number of bright galaxies observed in the new images, meaning they were consistent with the standard model of the universe.

But the model is still up for debate. There’s no question about Webb’s impact on space science, however. As the telescope continues to beam new images back home, it will continue to fuel bursts of research – and wonder – on Earth.