Reviewed by Lexie CornerNov 13 2024
According to new research from Case Western Reserve University, the oldest galaxies are big and bright, which aligns with an alternative theory of gravity. These findings were published in The Astrophysical Journal.
The standard model of galaxy formation in the early universe predicted that the James Webb Space Telescope (JWST) would detect faint signals from small, primitive galaxies. However, the data do not support the widely accepted hypothesis that invisible dark matter played a role in helping the earliest stars and galaxies cluster together.
These findings challenge astronomers' theories about the early universe.
What the theory of dark matter predicted is not what we see.
Stacy McGaugh, Astrophysicist, Case Western Reserve University
McGaugh, the director of astronomy and a professor at Case Western Reserve, proposed that modified gravity, rather than dark matter, could explain the observations. He pointed to the Modified Newtonian Dynamics (MOND) theory, introduced in 1998, which predicted that the structure formation in the early universe would have occurred much more quickly than the Cold Dark Matter (lambda-CDM) theory suggests.
The James Webb Space Telescope (JWST) was designed to address key questions about the universe, such as how and when galaxies and stars first formed. When it was launched in 2021, it was the first telescope capable of observing such distant regions of space and time.
According to the lambda-CDM model, galaxies form through the gradual accumulation of matter, from small to large structures, with dark matter providing additional gravity to facilitate this process.
McGaugh added, “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.”
The small pieces came together to form ever-larger structures, eventually forming galaxies. These tiny galaxies should appear as faint light to JWST.
“The expectation was that every big galaxy we see in the nearby universe would have started from these itty-bitty pieces,” McGaugh added.
However, the signals observed by the James Webb Space Telescope (JWST) are brighter and larger than expected, even at higher redshifts, which correspond to earlier stages in the universe’s evolution.
According to MOND, the mass that eventually forms a galaxy initially expands outward with the rest of the universe after rapidly assembling. A galaxy forms when this material collapses in on itself as the stronger force of gravity slows and eventually reverses the expansion. This theory does not involve any dark matter.
More than 25 years ago, MOND predicted the large, bright structures that JWST detected in the early universe, McGaugh noted. He co-authored the study with former graduate student Jay Franck and Federico Lelli, a postdoctoral researcher at Case Western Reserve currently at the INAF–Arcetri Astrophysical Observatory in Italy. James Schombert of the University of Oregon is the fourth coauthor.
McGaugh concluded, “The bottom line is, ‘I told you so.’ I was raised to think that saying that was rude, but that is the whole point of the scientific method: Make predictions and then check which come true.”
He also mentioned that finding a theory that reconciles both MOND and General Relativity remains a significant challenge.
Journal Reference:
McGaugh, S. S. et. al. (2024) Accelerated Structure Formation: the Early Emergence of Massive Galaxies and Clusters of Galaxies. The Astrophysical Journal. doi.org/10.3847/1538-4357/ad834d