The unprecedented power of the James Webb Space Telescope allows it to look further back in space and time than ever before - and in doing so, it's revealing some puzzling galaxies that appear to be too advanced for their age. Now, astronomers have come up with a new explanation for them - "starburst" galaxies - that spares the Standard Model of cosmology.


An artist's view of "starburst" galaxies in the early universe/Aaron M. Geller, Northwestern University, CIERA+IT-RCD

To travel through space is to travel through time. For example, if astronomers look at a star 100 light-years away, they see it as it looked 100 years ago because its light took that long to reach us. So when you stretch it out to the very edge of the observable universe, you can actually look into the past more than 12 billion years ago -- a period known as the "cosmic dawn" when the first stars ignited and formed early galaxies.

The James Webb Telescope was the first telescope powerful enough to see so far into space and time. Astronomers expected to see "protogalaxies" that were still forming, but to their surprise, the galaxies discovered by the telescope appeared to be quite advanced and mature, similar to today's galaxies. And not just one or two outliers, but dozens. This isn't just weird, it has the potential to upend our entire understanding of how galaxies form, and may even call into question the Standard Model of Cosmology itself.

So in the new study, a team of astrophysicists led by Northwestern University used powerful computer simulations to investigate other ideas. In the process, they discovered the possibility of producing a signal that matched James Webb's observations.

The simplest way to estimate the mass and size of a galaxy, especially from great distances, is to look at its brightness, which is what Webb did for the early galaxies discovered. But the team's simulations show that galaxies at the dawn of the universe could reach the same brightness levels with much lower masses - all they had to do was go through a period of rapid star formation, which is exactly what the simulated galaxies did themselves.

Sun Guochao, lead author of the study, said: "The key is to reproduce a sufficient amount of light in a system in a short time. This happens either because the system is very massive or because it has the ability to produce large amounts of light quickly. In the latter case, the system does not need that much mass. If the star formation occurs in a burst, it will emit a flash. This is why we see several very bright galaxies."

Modern galaxies like the Milky Way tend to show steady star formation over time, but simulations suggest that lower-mass early galaxies are more likely to undergo a "starburst" phase, followed by a relatively quiet period until these older stars die and fuel the formation of the next generation of stars in another starburst period.

"Most of the light in a galaxy comes from the most massive stars," said Claude-André Faucher-Giguère, senior author of the study. "Because more massive stars burn faster, they live shorter lives. They quickly use up their fuel in nuclear reactions. Therefore, the brightness of a galaxy is more directly related to the number of stars it has formed over the past few million years than to the mass of the entire galaxy."

Of course, just because a simulation is possible, that doesn't mean that's how the real universe happens. Using other techniques to measure the masses of these galaxies, follow-up observations from the Webb telescope could help confirm the starburst hypothesis and bring relief to the Standard Model of cosmology. After all, how could the formation of starbursts explain the emergence of other higher-order structures, such as barred galaxies, earlier than they should have?

The research was published in Astrophysical Journal Letters.