Cosmic Afterglow Revelation May 'Rewrite the History of the Universe'

Newsweek

13-05-2025

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Findings from a new study into the cosmic "afterglow" may rewrite the history of the universe, according to researchers.
This afterglow—the "cosmic microwave background" (CMB), the relic radiation left behind by the Big Bang—has given astronomers insights into the birth of the universe and helped shape the standard model of cosmology.
However, new research has calculated that the strength of this afterglow may have been overestimated—a fact that would call the standard model into question.
"According to our calculations," explained paper author and University of Bonn astrophysicist professor Pavel Kroupa in a statement, "it could be that this background radiation doesn't exist at all.
"At the very least, we are convinced that its strength has been underestimated."
Artist's impression of the Big Bang.
Artist's impression of the Big Bang.
coffeekai/Getty Images
In their study, Kroupa and his colleague Eda Gjergo, an astrophysicist at China's Nanjing University, studied elliptical galaxies, which are known to have been the first galaxies to form in the universe's infancy.
"We considered multiple well-established properties of massive early-type (elliptical) galaxies, and without altering them, we reconstructed their luminosity evolution," Gjergo told Newsweek.
He added: "These galaxies formed rapidly, with extremely high star formation rates, producing vast numbers of massive stars."
In fact, the duo explain, the process that saw vast volumes of gas accumulate into hundreds of billions of stars in these earliest galaxies only last a few hundred million years—this, Gjergo notes, "is relatively short on a cosmological time scale."
Gjergo told Newsweek that elliptical galaxies are "already among the brightest objects in the universe. However, their current luminosity comes primarily from ancient, low-mass stars, which are intrinsically very bright."
(In contrast, massive stars shine bright and die young.)
Gjergo continued: "We find that at the peak of their formation, elliptical galaxies must have been 10,000 times brighter than their counterparts today. We came up with the analogy of seeing 'embers in the ashes of ancient cosmic bonfires.' "
By measuring how far apart elliptical galaxies are today, and factoring in the rate at which the universe is thought to be expanding, the researchers were able to determine when exactly it was that elliptical galaxies first formed.
"The light these stars in all these galaxies emitted whilst forming is still around today as a background seen in all directions, and this background light essentially happens to more or less coincide with the observed CMB," Kroupa told Newsweek.
"Our most conservative estimate tells us that at least one percent of the CMB is from these stars in the forming elliptical galaxies."
"Since the fluctuations in the CMB are merely one thousandth of a percent, this means that the currently understood physics of the CMB is completely incorrect."
Previous research concluded that the CMB has small, localized differences in intensity—a fact which had been interpreted as proof that gas was not uniformly distributed across the burgeoning cosmos after the Big Bang.
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The new findings beg the question of how reliable such interpretations can be if elliptical galaxies account for at least 1.4 percent of the total measured radiation previously attributed to the CMB.
This, Kroupa said in a statement, may present "a problem for the standard model of cosmology.
"It might be necessary to rewrite the history of the universe, at least in part."
He told Newsweek that the unexpected result "upsets the usual interpretation of the nature of the CMB. It essentially means that we do not have solid evidence for a hot big bang. Taking the observed CMB and subtracting this foreground leaves too little for the hot big bang to be real."
(The "hot big bang" refers to how the universe started in a hot, dense, state and has been cooling and expanding ever since.)
Kroupa added: "This shocking result means that we now need to revisit the very foundations of everything we know about cosmology, gravitation and the evolution of the Universe and how galaxies came to be."
According, the researchers reported, they are now developing an entirely new model—which they dub the "Bohemian Model of Cosmology"—which has no hot big bang, no dark matter, no dark energy and no inflation.
This, Kroupa said, is "a significantly simpler and, it seems, better and much improved representation of the observed universe."
Gjergo added: "With this work, we identified the problem. Next, we aim to model the detailed imprint that we expect this early galaxy radiation must have left behind.
"What type of spectral features did these galaxies have during their prime? And how did they evolve to the present?"
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Reference
Gjergo, E., & Kroupa, P. (2025). The impact of early massive galaxy formation on the cosmic microwave background. Nuclear Physics B, 1017. https://doi.org/10.1016/j.nuclphysb.2025.116931