New observations from the James Webb Space Telescope (JWST) are challenging long-standing assumptions about the role of dark matter in galaxy formation, potentially lending support to an alternative theory known as Modified Newtonian Dynamics (MOND).
This recent data from JWST reveals that galaxies in the early universe are much larger and brighter than the standard dark matter model predicts, suggesting that these structures formed more rapidly than previously expected. Developed decades ago, MOND presents an alternative gravitational theory that may account for these early, massive galaxies without requiring the influence of dark matter, according to new research from Case Western Reserve University.
Unprecedented Early Galaxies in Webb’s View
The prevailing cosmological model, based on dark matter, holds that invisible matter provides additional gravitational force, which draws gas and stars together to form galaxies. This model predicts that galaxies would evolve slowly, gradually coalescing from smaller structures over billions of years. Based on these principles, astronomers expected JWST to reveal faint, small protogalaxies in the early universe. However, recent JWST images instead show large, luminous galaxies appearing much earlier in cosmic history, a finding that has left astronomers rethinking their assumptions.
“What the theory of dark matter predicted is not what we see,” said Stacy McGaugh, astrophysicist and professor at Case Western Reserve, whose study challenges the role of dark matter in early galaxy formation. In contrast, MOND—a theory developed to explain the behavior of galaxies without requiring dark matter—had anticipated that large galaxies could appear rapidly in the early universe. Originally proposed by physicist Mordehai Milgrom in the 1980s, MOND suggests that gravity operates differently under low-acceleration conditions, particularly at vast distances. With this adjusted gravitational force, MOND allows for rapid galaxy formation without dark matter, in a way that aligns with JWST’s surprising observations of the early universe.
Modified Newtonian Dynamics: An Alternate Path to Galaxy Formation
MOND diverges significantly from traditional gravitational theories by proposing that gravity behaves differently at extremely low accelerations, such as those on the edges of galaxies. While MOND has long remained a minority view in astrophysics, it predicted some aspects of early galaxy formation that dark matter models did not. McGaugh’s team found that the mass and brightness of JWST’s observed galaxies fit closely with MOND’s prediction of rapid structure formation. “The bottom line is, ‘I told you so,’” McGaugh remarked, highlighting MOND’s success in forecasting the nature of these early galactic structures. “I was raised to think that saying that was rude, but that’s the whole point of the scientific method: make predictions and then check which come true,” he added.
The MOND model proposes that galaxies in the early universe could have formed as large, cohesive structures rather than assembling gradually from smaller pieces. As McGaugh explains, “Astronomers invented dark matter to explain how you get from a very smooth early universe to big galaxies with lots of empty space between them that we see today.” MOND instead posits that galaxies may have initially expanded outward with the universe itself before gravitational forces reversed this expansion, causing the material to collapse in on itself to form dense galactic structures—all without the need for dark matter.
Study Publication and Implications for Cosmology
The study, published in The Astrophysical Journal on November 12, 2024, was co-authored by McGaugh along with Federico Lelli from Italy’s INAF–Arcetri Astrophysical Observatory, Jay Franck (formerly of Case Western Reserve), and James Schombert from the University of Oregon. The team’s findings support MOND’s predictive power and suggest that it could provide explanations for galactic structure formation that dark matter models may not. However, integrating MOND fully with other aspects of modern cosmology remains challenging, and the researchers acknowledge the complexities of balancing MOND with widely accepted theories like general relativity.
As Phys.org highlights, while MOND has shown predictive successes, it remains limited in scope and faces hurdles in explaining certain cosmological observations that dark matter currently addresses. Despite this, the recent JWST findings suggest that MOND could provide a valuable perspective on galaxy formation and gravitational forces under specific conditions in the universe. “Finding a theory compatible with both MOND and general relativity is still a great challenge,” McGaugh noted, pointing to the need for further research and exploration to reconcile these theories with the full range of cosmic observations.
Rethinking Dark Matter’s Role in Cosmic Evolution
The JWST data has prompted renewed interest in MOND as a possible explanation for the structure of the early universe, a reminder that fundamental cosmological questions remain unanswered. While the dark matter model has been the primary lens through which scientists understand the large-scale structure of the cosmos, this research indicates that it may not fully capture the universe’s complexity, especially at its earliest stages. MOND’s potential compatibility with these observations opens the door to further investigations into alternative models of gravity and galaxy formation.
For now, JWST’s observations add fuel to the ongoing debate about the nature of dark matter and the forces that shape galaxies. As JWST continues to push the boundaries of deep space observation, additional data may provide the insights necessary to clarify the roles of dark matter and modified gravity in shaping the universe. Whether MOND will eventually gain more traction, or if an entirely new framework will emerge to accommodate these findings, remains to be seen, but JWST’s revelations underscore that our understanding of the cosmos is still evolving in unexpected ways.