💥 Major discovery for the future of the Universe: its expansion called into question

For nearly three decades, astronomers have interpreted the faint luminosity of certain distant explosive stars as a sign of the Universe's runaway expansion. An inexorable acceleration, attributed to a ubiquitous dark energy. A team of researchers now proposes a radically different interpretation of these light signals. Their analysis suggests that these cosmic beacons, a special type of supernova, may have misled us about the fate of the Universe.

This questioning is based on a meticulous reassessment of the data that formed the basis of the standard cosmological model. Type Ia supernovae, used as "standard candles" to measure intergalactic distances, may not be as reliable as previously thought. Their intrinsic luminosity appears to be correlated with the age of the progenitor stars, a variable that had been overlooked until now. This discovery paves the way for a profound revision of our understanding of cosmic dynamics and the very nature of dark energy.

A fundamental flaw in our measuring instruments

The primary tool for mapping the expansion of the Universe relies on the observation of Type Ia supernovae. The basic postulate is that their peak luminosity is constant, making them ideal distance markers. By comparing their apparent brightness to their assumed actual brightness, astronomers deduce their distance. This principle led to the conclusion that distant supernovae were fainter than expected, indicating an accelerated expansion. This was the first indirect evidence for the existence of a dark energy counteracting the effect of gravity.

However, this assumption of uniform luminosity is now being challenged. The study published in Monthly Notices of the Royal Astronomical Society demonstrates that the standardized luminosity of these supernovae is systematically influenced by the age of the host galaxy. Supernovae from young stellar populations appear fainter than those from older stars. This correlation, established with a high level of statistical confidence (over 99.99%), introduces a significant bias in the interpretation of observations.

Indeed, by looking far into the Universe, we are necessarily looking into the past, to a time when stars were on average younger. The simple effect of stellar evolution can therefore create the illusion of an accelerating Universe, without the need for dark energy to explain it. This discovery casts serious doubt on the solidity of the observational evidence that earned the Nobel Prize in Physics in 2011.

The implications of a decelerating universe

Correcting for this age bias profoundly alters the reading of the history of cosmic expansion. The data recalculated by the team from Yonsei University no longer support the scenario of a current acceleration. On the contrary, they indicate that the Universe may have already entered a phase of deceleration. This transition would mark a cosmological turning point, indicating that the dominance of dark energy might only be temporary.


This perspective is reinforced by independent results, such as those from the DESI instrument, which have also pointed towards a possible evolution of dark energy. The convergence of these clues paints a picture of a force that is not constant, but dynamic. If dark energy weakens over time, its battle against gravity could see a reversal. Widespread contraction would then become a plausible scenario for the distant future.

The consequences are considerable for theoretical cosmology. The ΛCDM model, a pillar of modern cosmology that describes a Universe with a fixed cosmological constant, would need to be revised. This questioning opens the door to other models where dark energy is a dynamic scalar field. The fate of the Universe, whether "Big Freeze" or "Big Crunch," must therefore be entirely reconsidered, making this question one of the major challenges for research in the coming years.

To go further: What is a Type Ia supernova?

A Type Ia supernova is the cataclysmic thermonuclear explosion of a white dwarf in a binary system. This stellar corpse accumulates matter stripped from a companion star. When it reaches a critical mass, the pressure and temperature at its core trigger an uncontrollable fusion reaction. The star is completely disrupted.


The particularity of these events lies in their triggering mechanism. The critical mass is always the same. This produces an explosion whose energy is also always the same. This regularity makes them valuable tools for astronomers, serving as luminosity standards for probing the Universe.

However, new studies suggest that the environment and age of the progenitor star influence the amount of radioactive nickel synthesized. This nickel is the main source of the light. Slight variations in its production could explain the observed differences in luminosity, challenging their status as a perfect standard.

What is the "Big Crunch"?

The "Big Crunch" is a theoretical scenario for the end of the Universe. It assumes that cosmic expansion will eventually stop, then reverse under the dominant effect of gravity. All matter and energy would then begin to come closer together, leading to a widespread contraction.

This contraction phase would be the temporal mirror of the Big Bang. The Universe would become increasingly hot and dense. Galaxies would eventually collide, and structures would dissolve in a bath of increasingly energetic radiation. The ultimate fate would be a state of infinite density and temperature.

This scenario is only conceivable if the total density of the Universe exceeds a critical value. It also requires that dark energy, which acts as a repulsive force, is not constant. If it weakens or becomes attractive, gravity could prevail, making the "Big Crunch" possible again.

What is the ΛCDM model?

The ΛCDM model is the standard theoretical framework in cosmology. It describes a Universe composed mainly of dark energy, symbolized by the cosmological constant Λ, and cold dark matter. Ordinary matter, which makes up stars and planets, represents only a tiny fraction.


This model is based on Einstein's theory of General Relativity. It has been remarkably successful in explaining a wide range of observations. It accurately predicts the cosmic microwave background, the formation of large-scale structures, and the abundance of light elements formed after the Big Bang.

However, observational tensions are emerging. The value of the Hubble constant measured locally differs from that deduced from the cosmic microwave background. The possible evolution of dark energy, suggested by recent studies, might require an extension or modification of this foundational model.

Article author: Cédric DEPOND