According to a recent study, some of the earliest galaxies observed with the James Webb Space Telescope are actually significantly less massive than initially thought. The presence of black holes in these galaxies causes them to appear brighter and larger than their true size. This information sheds light on the discussion surrounding the necessity of changing the standard model of cosmology based on the size of early galaxies.
When astronomers first glimpsed galaxies from the early universe using NASA’s James Webb Space Telescope, they anticipated observing tiny galaxies, but instead, they encountered what seemed to be an array of massive galaxies. Some galaxies looked like they had gained enormous mass in a remarkably short time, which simulations struggled to explain. This led some researchers to propose that this might indicate flaws in the standard model of cosmology—a theoretical framework that describes the universe’s composition and its evolution since the big bang.
A new study published in The Astrophysical Journal, led by Katherine Chworowsky, a graduate student at the University of Texas at Austin, reveals that a number of these early galaxies are indeed much less massive than previously believed. The black holes located within these galaxies contribute to their brightness, making them appear larger than they actually are.
“We still observe more galaxies than predicted, but none are so massive that they violate the rules of the universe,” Chworowsky stated.
The findings were made possible by observations from Webb’s Cosmic Evolution Early Release Science (CEERS) Survey, spearheaded by Steven Finkelstein, an astronomy professor at UT and a co-author of the study.
Black Holes Increase Brightness
This latest research indicates that many of the galaxies that seemed overly massive likely host black holes that are rapidly consuming gas. The friction generated by this fast-moving gas produces heat and light, causing these galaxies to shine much brighter than would be expected if the light came solely from stars. This increase in brightness can give the false impression that these galaxies have many more stars—and are therefore more massive—than our estimates suggest. When scientists excluded these so-called “little red dots” (named for their color and small size) from their calculations, the remaining early galaxies fit well within the predictions of the standard cosmology model.
“In conclusion, the standard model of cosmology is not in crisis,” Finkelstein said. “For a theory that has held up for so long, it requires significant evidence to overturn it, which simply isn’t the case here.”
Highly Efficient Star Formation
While the main issue has been addressed, another, lesser concern persists: Webb’s data shows there are still roughly twice as many massive galaxies in the early universe as anticipated by the standard model. One theory for this discrepancy is that stars formed at a quicker pace in the early universe than they do today.
“Perhaps in the early universe, galaxies were more effective at transforming gas into stars,” Chworowsky suggested.
Star formation occurs when hot gas cools sufficiently to be pulled together by gravity to form one or more stars. However, as the gas collapses, it heats up, creating outward pressure. In our part of the universe, this balance between opposing forces generally slows down the star formation process. Some theories speculate that due to higher density in the early universe, gas blowout during star formation was limited, enabling the process to occur more swiftly.
Evidence for Black Holes
At the same time, astronomers have been studying the spectra of the “little red dots” discovered using Webb, with researchers from both the CEERS team and others identifying signs of fast-moving hydrogen gas, which is indicative of black hole accretion disks. This finding supports the notion that much of the brightness from these compact, reddish objects may stem from gas swirling around black holes rather than from stars—backing up the conclusion of Chworowsky’s team that these galaxies might not be as massive as initially believed. Nonetheless, additional observations of these intriguing objects are forthcoming and will help clarify the source of light, whether from stars or from gas surrounding black holes.
In science, resolving one question often opens the door to new inquiries. Although the researchers have indicated that the standard model of cosmology is likely intact, their findings underscore the need for fresh perspectives on star formation.
“Yet, there remains a sense of curiosity,” Chworowsky noted. “Not everything is entirely understood. This uncertainty is what makes scientific exploration enjoyable; it would be dull if a single paper resolved all issues, leaving no questions left to explore.”
Other authors from UT involved in the research are Michael Boylan-Kolchin, Anthony Taylor, and Micaela Bagley. They, along with Finkelstein (the director) and Chworowsky, are part of UT’s Cosmic Frontier Center, which aims to deepen our understanding of the early universe.
This research involved collaborations from institutions including Colby College, University of Toronto, Texas A&M University, the National Optical-Infrared Astronomy Research Laboratory of the National Science Foundation, NASA Goddard Space Flight Center, University of Connecticut, European Space Astronomy Centre, University of Massachusetts Amherst, University of California at Irvine, Centro de AstrobiologÃa (Spain), The Hebrew University of Jerusalem, Cosmic Dawn Center (Denmark), University of Copenhagen, Flatiron Institute, University of Louisville, Universidad de la Laguna, Université Paris Cité, Swiss Federal Institute of Technology Lausanne, Rochester Institute of Technology, University of Padua (Italy), INAF — Padua Astronomical Observatory (Italy), University of California at Riverside, University of Sussex, University of Malta, University of Groningen, SRON Netherlands Institute for Space Research, and the National Astronomical Observatory of Japan.
This research was funded by NASA, the Space Telescope Science Institute, and the National Science Foundation.
The James Webb Space Telescope is an international initiative led by NASA in partnership with the European Space Agency and the Canadian Space Agency.
