The Standard Model predicted that the NASA/ESA/CSA James Webb Space Telescope would observe a faint signal from a small protogalaxy. However, the common hypothesis that invisible dark matter contributed to the clumping of early stars and galaxies is not supported by the data. In fact, a new study led by astrophysicists at Case Western Reserve University says that the fact that the oldest galaxies are larger and brighter is consistent with another theory of gravity.
This artist's impression shows the evolution of the universe, starting with the Big Bang on the left and continuing with the emergence of the Cosmic Microwave Background. The formation of the first stars ends the Dark Ages of the universe, followed by the formation of galaxies. Image credit: M. Weiss / Harvard-Smithsonian Center for Astrophysics.
“What dark matter theory predicts is not what we're seeing,” says Case Western Conservancy Professor Stacey McGaw.
“Instead of dark matter, modified gravity may have played a role. A theory known as MOND (Modified Newtonian Mechanics) proposed in 1998 that structure formation in the early universe would have occurred very quickly. It's much faster than the cold dark matter theory known as lambda CDM predicted.
The Webb is designed to answer some of the universe's biggest questions, such as when and how stars and galaxies formed.
Until its launch in 2021, there was no telescope that could peer deep into space and far back in time.
Lambda CDM predicts that galaxies formed by the gradual accretion of matter from smaller structures to larger structures due to the extra gravity provided by the mass of dark matter.
“Astronomers invented dark matter to explain how we went from a very smooth early universe to the large galaxies we see today with lots of space in between.” Professor McGough said.
Smaller pieces clustered into larger structures until galaxies formed. Webb should be able to see these tiny galaxy precursors as dim lights.
“All the large galaxies we see in the nearby universe were expected to have started from these tiny pieces,” Professor McGough said.
But even at higher and higher redshifts, the signal is larger and brighter than expected, even from this early stage of the universe's evolution.
MOND predicted that the mass that would become galaxies would rapidly aggregate and initially expand outward with the rest of the universe.
The stronger gravity slows the expansion, which then reverses and the matter collapses on itself to form galaxies. In this theory, dark matter does not exist at all.
“The large, bright structures that Webb saw in the very early days of the universe were predicted by MOND more than a quarter of a century ago,” Professor McGough said.
“The bottom line is, “I told you so.'' I was raised to think it was rude to say that, but that's the whole point of the scientific method, to make predictions and find out which ones. Let's see if it becomes a reality.”
“Finding a theory that fits both MOND and general relativity remains a major challenge.”
of the team paper will appear in today's astrophysical journal.
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Stacey S. McGaw others. 2024. Accelerating structure formation: The early emergence of massive galaxies and galaxy clusters. APJin press. arXiv: 2406.17930
This article is a version of a press release provided by Case Western Reserve University.
Source: www.sci.news
