Scientists have tested the main theory about dark energy
Dark energy has long been considered the main explanation for the accelerated expansion of the universe. However, a new international study based on the largest and most homogeneous catalog of Type Ia supernovae has shown that the data is slightly better consistent with a model in which the properties of dark energy change over time. The article in Izvestia explains why the results do not allow us to talk about the discovery yet, but force scientists to take a closer look at alternative cosmological models.
Dark energy has stopped being a constant again
In the late 1990s, astronomers discovered that the universe was expanding not just after the Big Bang, but was doing so with acceleration. To explain this phenomenon, dark energy has been proposed, an unknown form of energy that, according to modern concepts, makes up most of the energy content of the universe.
The basis of modern cosmology remains the ΛCDM (lambda-CDM) model. She suggests that dark energy is a cosmological constant — that is, its properties do not change with time.
However, in recent years, several independent observations have begun to indicate possible deviations from this picture. The new study does not refute the standard model, but shows that the available data weakly prefer a scenario in which the properties of dark energy can change as the universe evolves.
At the same time, the authors themselves emphasize that statistical significance is not yet sufficient to consider such a hypothesis confirmed. The work has been published in the journal Phys.org .
How distant stars help to measure the universe
The authors of the study created the Unite catalog by combining data from two of the largest type Ia supernova observation projects, Pantheon+ and DES-SN5YR. The final sample included information on 2,884 probable Type Ia supernovae, making Unite the most comprehensive and internally consistent dataset of its kind to date.
To achieve maximum comparability of the results, the researchers re-processed an almost 30-year-old array of observations, using a single methodology for modeling supernovae, selecting objects and correcting systematic effects. In addition, the masses of the galaxies in which the outbursts occurred were overestimated using a single approach for most of the sample.
Type Ia supernovae are powerful stellar explosions that occur in a certain type of binary star system. They play a special role in cosmology. Since their luminosity after standardization is well known, they serve as a kind of "standard candles". Due to the relatively predictable brightness of such explosions, astronomers use them as a kind of "standard candles" — based on the observed brightness of a supernova, the distance to its galaxy can be estimated. This allows us to study how the universe is expanding and whether the rate of this expansion has changed over time.
By comparing the true and observed brightness of such flares, astronomers can determine the distances to distant galaxies and track how the expansion rate of the universe has changed throughout its history.
The data again hinted that dark energy is changing
After analyzing the combined catalog, the researchers compared the results with the predictions of the standard ΛCDM model. It turned out that the new data again gives a slight advantage to models in which dark energy can change over time.
As noted by astrophysicist Tamara Davis, similar hints have already appeared when analyzing data from the Dark Energy Survey (DES), and similar results were previously obtained by the Dark Energy Spectroscopic Instrument (DESI) project. Thus, independent observations based on different cosmological measurements point in the same direction again.
Tamara Davis, astrophysicist
Two completely independent measurements revealed signs of dark energy changing over time, which calls into question the assumption of the standard model that dark energy does not change. All of these studies may also hold the key to explaining how gravity and quantum physics are interconnected.
However, the authors themselves urge caution. Bayesian analysis shows only a weak preference for the model with varying dark energy, and with frequency analysis, the statistical significance is about 2.5σ (standard deviation) or 3.1σ, depending on the calculation method. Recognition of a discovery in physics usually requires a level of about 5σ.
Why aren't scientists rushing to rewrite textbooks yet
Despite the intriguing results, the researchers do not believe that the standard cosmological model has been refuted. The ΛCDM still successfully explains a huge number of astronomical observations and remains the most reliable description of the evolution of the universe.
The new work only reinforces interest in the hypothesis that the properties of dark energy may be more complex than previously thought. To test this idea, scientists will need new independent observations and even larger samples of supernovae.
If future studies confirm the current signals, this may lead to a revision of one of the key provisions of modern cosmology. In the meantime, the authors emphasize that the existing results should be considered as an important reason for further research, and not as definitive evidence of changing dark energy.
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