Dark energy may be changing, according to a study of 3,000 supernovae

A catalog of 2,884 type Ia supernovae, combined with observations from the DES and results from DESI, offers new signals that dark energy may change over time and raises tensions for the standard model of cosmology.

• The analysis of type Ia supernovae finds indications of dark energy that may not be constant.
• The results add to independent observations from the Dark Energy Survey and the Dark Energy Spectroscopic Instrument.
• New data could help study the relationship between Einstein's gravity and quantum physics, although the signal does not yet constitute definitive confirmation.

A catalog of 2,884 type Ia supernovae offers new signals that dark energy may be evolving. This mysterious component explains, within the dominant cosmological model, the acceleration of the universe's expansion, but the new analysis suggests that its influence may not necessarily remain fixed from the past to the present.

The work reconstructed three decades of astronomical observations under a common framework and combined them with measurements from the Dark Energy Survey, as well as data on the relic light from the Big Bang and the distribution of galaxies. According to the researchers, the result does not fully confirm the standard model, which assumes a constant and unchanging dark energy, but rather provides additional evidence in favor of a possible temporal variation.

Supernovae as cosmic rulers

Type Ia supernovae are especially valuable because their explosions produce a sufficiently uniform amount of light to function as standard candles. By comparing the expected brightness with the observed brightness from Earth, astronomers can estimate cosmic distances and study how much the universe has expanded during the journey of that light.

The origin of these explosions is related to white dwarfs, the compact remnants left when stars with a mass similar to that of the Sun exhaust their fusion fuel. In a solitary star, that remnant usually represents the end of the process, but a binary companion can completely change its fate by supplying material to the white dwarf.

A significant proportion of Sun-like stars are part of binary systems. When both stars are close enough, the white dwarf can accumulate material from its companion. In certain scenarios, that process can trigger a type Ia thermonuclear explosion, although the details of the progenitor systems remain under study.

Ryan Camilleri, a member of the team from the University of Queensland, explained that researchers were able to apply a more precise understanding of the behavior of these supernovae to ancient observations. This review allowed for the comparison of data obtained by different telescopes and reduced errors that could distort conclusions about distances, redshift, and cosmic expansion.

A signal that challenges the standard model

The analysis took into account factors that affect the light from a supernova before it reaches Earth, such as cosmic dust and the mass of the host galaxy. It also incorporated gravitational lensing, an effect that bends and can amplify light when it passes through regions near massive objects, with the aim of building a more consistent comparison between the observed events.

The research adds to results released in 2024 by the Dark Energy Spectroscopic Instrument, known as DESI, which also found indications of variable dark energy while studying the acoustic waves left by the early universe. The importance of the comparison lies in the fact that the two approaches observe different phenomena and still point to a possible deviation from constant dark energy.

The team also contrasted its measurements with results from the Dark Energy Survey, whose published supernova data in 2024 had shown signs that dark energy could vary over time. This compilation observes a deviation from the standard model in a slightly different direction, so it will still be necessary to resolve the differences between the datasets.

The match does not equate to a definitive confirmation that dark energy is changing, because cosmological measurements depend on calibrations, models, and sources of uncertainty. However, the results from DES, DESI, and the new catalog keep open the possibility that dark energy does not maintain exactly the same influence throughout cosmic history.

What Could Change in Physics

Determining the nature of dark energy could have consequences that go beyond explaining the accelerated expansion of the universe. The research suggests that the problem could also provide clues on how to connect Albert Einstein's general relativity, which describes gravity on a large scale, with quantum physics, which explains the behavior of matter and energy on subatomic scales.

Both theories have demonstrated enormous predictive power within their respective realms, but scientists still lack a complete theory of quantum gravity. If the evolution of dark energy reveals a physical structure that does not fit with current explanations, it could open a pathway to study that pending union between gravity and quantum mechanics. For now, it remains a theoretical possibility and not a consequence demonstrated by the new catalog.

The next stage will depend, in part, on expanding the catalog of type Ia supernovae and improving consistency between observations made with different instruments. The Dark Energy Bedrock All-Sky Supernova program, known as DEBASS, is detecting hundreds of additional local supernovae, a sample that could help test the discrepancies observed by DES, DESI, and the analysis of supernovae.

For now, the main conclusion is not that the standard model has been discarded, but that its assumption of immutable dark energy is facing increasing pressure. More data will allow us to determine whether the signals reflect a real property of the universe, a limitation in the measurements, or a combination of both factors.