"Red Monsters" Challenge Theories of Early Galaxy Formation

According to a study published in Nature, an international team headed by the University of Geneva (UNIGE) discovered three ultra-massive galaxies, almost as huge as the Milky Way, during the first billion years following the Big Bang.

The FRESCO program of the James Webb Space Telescope, which employs the NIRCam/grism spectrograph to estimate precise distances and star masses of galaxies, made this unexpected discovery possible.

The findings cast doubt on previous theories of galaxy formation by demonstrating that star production in the early Universe was significantly more efficient than believed.

Scientists prefer the theoretical model that galaxies develop over time in huge halos of dark matter. These halos capture gas (molecules and atoms) into gravitationally bound formations, only 20 % of which is transformed into stars within galaxies.

Recent research uncovered by a global team led by UNIGE using NASA's James Webb Space Telescope (JWST) disputes this theory. It reveals that huge galaxies throughout the early Universe could have built stars more efficiently than their later counterparts, growing much quicker than previously considered.

JWST’s exceptional capabilities have enabled astronomers to systematically research galaxies in the distant and early Universe, offering insights into large and dust-obscured galaxies. Researchers discovered that most galaxies in the FRESCO study fit known models.

The scientists also discovered three surprisingly large galaxies with stellar masses like the Milky Way. These create stars roughly twice as effectively as their lower-mass counterparts and later galaxies. They are known as the three “Red Monsters” because of their high dust content, which causes them to appear red in JWST images.

Our findings are reshaping our understanding of galaxy formation in the early Universe.

Mengyuan Xiao, Stude Lead Author and Postdoctoral Researcher, Department of Astronomy, University of Geneva

“The massive properties of these ‘Red Monsters’ were hardly determined before JWST, as they are optically invisible due to dust attenuation,” added Dr. David Elbaz, director of research at CEA Paris-Saclay.

The global team has collaborated with the JWST to create a new program to systematically assess a complete sample of emission-line galaxies from the first billion years of cosmic history. This method allowed the researchers to obtain precise distance estimations and accurate stellar mass measurements for the entire galaxy sample.

Our findings highlight the remarkable power of NIRCam/grism spectroscopy. 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.

Pascal Oesch, Associate Professor, Department of Astronomy, University of Geneva

While these findings do not challenge the traditional cosmological model, they raise fresh queries about galaxy formation hypotheses, particularly the dilemma of "too many, too massive" galaxies in the early Universe.

Current models should likely consider the processes that enabled large early galaxies to accomplish such efficient star formation and form quickly and early in the Universe. Future observations with JWST and the Atacama Large Millimeter Array will offer additional information about these huge “Red Monsters” and show a larger sampling of such sources.

Xiao concluded, “These results indicate that galaxies in the early Universe could form stars with unexpected efficiency. As we study these galaxies in more depth, they will offer new insights into the conditions that shaped the Universe’s earliest epochs. The 'Red Monsters' are just the beginning of a new era in our exploration of the early Universe.”

Journal Reference:

Xiao, M. et. al. (2024) Accelerated formation of ultra-massive galaxies in the first billion years. Nature. doi.org/10.1038/s41586-024-08094-5