In the dark reaches of the early universe, three monstrous galaxies were already lurking — a mere billion years after the Big Bang. These galaxies, nearly as massive as our own Milky Way, were just uncovered by an international team led by the University of Geneva (UNIGE). The discovery was made possible by the cutting-edge capabilities of the James Webb Space Telescope (JWST). And it is sending ripples through the world of astronomy.
The discovery is challenging long-held ideas about how galaxies formed in the early days of the cosmos. In theory, galaxies take shape within large halos of dark matter, which attract gas to form stars. Yet, these newly discovered galaxies seem to have found a shortcut, growing into behemoths much faster than scientists believed was possible.
Monsters Among Stars
These galaxies have earned the nickname “red monsters,” thanks to their reddish appearance in the JWST images — a telltale sign of high dust content. Dust usually obscures starlight, making such galaxies invisible to conventional telescopes. But JWST’s powerful NIRCam/grism spectrograph has pierced through the cosmic haze. It revealed not just the presence of these galaxies but their astonishing mass and rapid star formation.
“Our findings are reshaping our understanding of galaxy formation in the early universe,” says Dr. Mengyuan Xiao, the study’s lead author and postdoctoral researcher in the Department of Astronomy at the University of Geneva. The galaxies seem to break all the rules: they’re forming stars at twice the rate of their smaller peers and doing so with remarkable efficiency.
For Dr. David Elbaz, director of research at CEA Paris-Saclay, these findings mark a turning point. “The massive properties of these ‘red monsters’ were hardly determined before JWST, as they are optically invisible due to dust attenuation.”
Galaxies That Defy Theory
The JWST’s FRESCO program, developed by the team, systematically analyzed emission-line galaxies from the dawn of the universe. This allowed them to accurately measure the distances and stellar masses of these newly detected giants.
“Our findings highlight the remarkable power of NIRCam/grism spectroscopy,” notes Pascal Oesch, associate professor at UNIGE and principal investigator of the study. “The instrument on board the space telescope allows us to identify and study the growth of galaxies over time, and to obtain a clearer picture of how stellar mass accumulates over the course of cosmic history.”
According to established models, galaxies form gradually, converting no more than 20% of their gas into stars. But the “red monsters” upend that notion. Because their stellar masses are on par with today’s Milky Way, they suggest a much more efficient process at work in the universe’s infancy.
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“These results indicate that galaxies in the early universe could form stars with unexpected efficiency,” Dr. Xiao explains. This rapid growth raises a thorny question: how did these galaxies accumulate so much mass so quickly?
These discoveries don’t overthrow existing cosmological models, but they do hint at gaps in our understanding. Astronomers are now pondering what unique processes might have spurred such efficient star formation in the universe’s early days.
The study is only the beginning of a new era in cosmic exploration. The team plans to use JWST and the Atacama Large Millimeter Array (ALMA) to search for even more of these hidden giants.
As Dr. Xiao puts it, “The red monsters are just the beginning of a new era in our exploration of the early universe.”
The findings were reported in the journal Nature.
