Since it began operations in 2022, the James Webb Space Telescope (JWST) has allowed scientists to make incredible strides in our understanding of the cosmos — especially its early epoch. However, one lingering cosmological mystery that the JWST hasn’t had a major impact on is the nature of dark matter. Now, new research suggests that this is something that may soon change.
While dark matter is estimated to account for 85% of the matter in the universe, it is difficult to investigate because it doesn’t interact with electromagnetic radiation (light) or it interacts so weakly that we can’t directly detect it. As well as making dark matter effectively invisible, this lack of interaction with light tells scientists that the particles making up dark matter aren’t the protons, neutrons, and electrons that comprise the everyday stuff we see around us on a day-to-day basis, ranging from the most massive stars to the viruses that make our lives miserable every winter. The search for a potential dark matter particle has delivered many suspects, but they’ve all remained frustratingly hypothetical.
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Studying these elongated galaxies with the JWST might help reveal the presence of dark matter, scientists say. “In the expanding universe defined by Einstein’s theory of general relativity, galaxies grow over time from small clumps of dark matter that form the first star clusters and assemble into larger galaxies via their collective gravity,” team member Rogier Windhorst, of Arizona State University, said in a statement.
“But now the JWST suggests that the earliest galaxies may be embedded in marked filamentary structures, which — unlike cold, dark matter — smoothly join the star-forming regions together, more akin to what is expected if dark matter is an ultralight particle that also shows quantum behavior.”
Understanding dark matter is a stretch
When using simulations to recreate how the first galaxies formed in the early universe, allowing cool gas to gather along the threads in a web of dark matter is able to quite nicely recreate the mostly spheroid galaxies we see in the modern universe.
However, as the JWST has been allowing astronomers to look back at galaxies that existed in the very early stages of the universe, they have increasingly been finding filamentary elongated galaxies that aren’t as easily recreated in simulations that stick to the standard mechanism of gas gathering to birth stars and grow galaxies.
To investigate this, Windhorst and colleagues looked at simulations of the universe involving different types of dark matter other than that found in the most accepted model of cosmology, the Lambda Cold Dark Matter (LCDM) model; “cold” dark matter, which doesn’t refer to temperature but instead to the speed at which particles move.
This revealed that the wave-like behavior of “fuzzy dark matter” or ultralight axion particles could account for the elongated morphology of early galaxies seen by the JWST.
“If ultralight axion particles make up the dark matter, their quantum wave-like behavior would prevent physical scales smaller than a few light-years from forming for a while, contributing to the smooth filamentary behavior that JWST now sees at very large distances,” team leader Álvaro Pozo of the Donostia International Physics Center said.
The team’s modelling also indicated that faster-moving “warm dark matter” particles, like sterile neutrinos, could also give rise to early filamentary galaxies. In both the wave dark matter and warm dark matter scenarios, this is because these particles give rise to smoother filaments than cold dark matter. As gas and stars slowly flow down these filaments, elongated galaxies begin to form.
The JWST will continue to investigate oddly shaped galaxies in the early universe, while researchers here on Earth continue to evolve simulations of the early universe. Bringing these together could eventually help solve the mystery of dark matter.
The team’s research was published on Dec. 8 in the journal Nature Astronomy.