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A catalog of nearly 3,000 white dwarfs that exploded as Type Ia supernovae after feeding excessively off their companion stars suggests that dark energy – the mysterious force that accelerates the expansion of the universe – – is transforming over time. This discovery, combined with data from the Dark Energy Survey (DES), confirms the results published by the Dark Energy Spectroscopic Instrument (DESI) in 2024, which indicated a weakening of dark energy’s influence. This means that the research team’s work not only encompasses the most comprehensive catalog of Type Ia supernovae but also provides the clearest picture yet of the evolution of the universe and the effects of dark energy.
“We have combined three decades of astronomical observations into a single, coherent framework,” said team member Ryan Camilleri of the University of Queensland in a statement. “We have supplemented our data with other cosmic measurements, including the Big Bang’s cosmic microwave background and maps of the spatial distribution of galaxies. “Rather than confirming the standard model of cosmology, which assumes that dark energy is stable and constant, we have further evidence that it is capable of changing over time.”
White dwarfs are smoldering stellar remnants left behind after stars with masses similar to that of the Sun exhaust the nuclear fuel in their cores. This stops the action of the outward pressure that protects the star from its own gravity, causing the stellar core to collapse and the outer layers to be shed. The core becomes a white dwarf, and for solitary stars, that is the end of the story. However, about 50% of Sun-like stars have binary companions, which can lead to a resurgence of activity and change the star’s fate.
If the white dwarf and its companion are close enough, the dead star begins to strip away the outer layers of its neighbor. As this material accumulates on the white dwarf, it exceeds the so-called Chandrasekhar limit, causing the stellar remnant to explode as a supernova.
These cosmic explosions are classified as Type Ia supernovae, and their luminosity is so consistent that such events are referred to as “standard candles.” They are of paramount importance because analyzing the redshift of their light as it travels allows Type Ia supernovae to be used to measure cosmic distances. “Over the years, we’ve gained a much better understanding of how supernovae behave, so we were able to go back and apply this updated knowledge to older data,” Camilleri explained. “A large-scale effort was undertaken to combine observations from various telescopes with different capabilities, and we also accounted for factors such as cosmic dust and the mass of galaxies, which can affect a supernova’s radiation. “We also incorporated more subtle effects, including gravitational lensing, which involves the bending and amplification of light as it passes near massive objects on its way to Earth.”
Combined with the DESI results from 2024, this study has the potential to revolutionize our understanding of the true nature of dark energy. “Our data on supernovae, obtained by DES in 2024, provided the first hints that dark energy may change over time, and this new compilation also records deviations from the standard model, albeit in a slightly different direction,” Davis noted. – Similarly, results from the DESI mission have revealed signs of fluctuations in dark energy while surveying relic sound waves from the early universe. Thus, two completely independent measurements have detected clues to the temporal variability of dark energy, challenging the standard model’s assumption that it is constant.”
Davis added that, in addition to shedding light on the nature of dark energy, this research could point the way toward unifying gravity and quantum physics. Although quantum physics (the best theory for describing the universe at the subatomic level) and Einstein’s general theory of relativity (the best model of gravity) have achieved tremendous success in their respective fields, scientists have not yet managed to reconcile them. In other words, there is no unified theory of quantum gravity.
“We know that both of these theories are extremely effective in their respective fields, so figuring out how to unify them would be a monumental step forward for theoretical physics,” Davis continued. This process will receive an additional boost after new data are integrated into the existing detailed catalog of Type Ia supernovae. Among them will be observations from the Dark Energy Bedrock All-Sky Supernova (DEBASS) program, which records hundreds of local supernovae on a much larger scale than even the DES survey.
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