This is the most in-depth analysis of dark energy and dark matter to date, according to the study authors.

New research suggests that 66.2 percent of the universe is dark energy and that the remaining 33.8 percent is made up of both dark energy and matter.

Astrophysicists have conducted a powerful new analysis that establishes the most precise constraints on the universe’s composition and development to date. Cosmologists are approaching a turning point with this analysis, known as Pantheon+.

Pantheon+ concludes that the universe is made up of roughly two-thirds dark energy and one-third matter — predominantly dark matter — and has been expanding at an accelerated rate over the last billion years.

However, Pantheon+ also solidifies a significant dispute regarding the rate of that expansion that hasn’t been resolved.

Pantheon+ further slams the door on alternative frameworks accounting for dark energy and dark matter by putting current modern cosmological ideas, such as the Standard Model of Cosmology, on even firmer evidentiary and statistical basis.

Both are pillars of the Standard Model of Cosmology, yet none has been explicitly discovered, making them two of the model’s greatest mysteries.

Based on the results of Pantheon+, scientists can now do more precise observational tests and fine-tune their explanations for the apparent cosmos.

The Center for Astrophysics | Harvard & Smithsonian’s Dillon Brout, an Einstein Fellow, adds that the Pantheon+ results provide for the most exact limits on the dynamics and history of the universe to date. 

“We’ve combed over the data and can now say with more confidence than ever before how the universe has evolved over the eons and that the current best theories for dark energy and dark matter hold strong.”

Brout is the primary author of several papers that collectively describe the new Pantheon+ analysis and were released today in a special issue of The Astrophysical Journal.

It uses the greatest dataset of Type Ia supernovae to date. White dwarf stars, the stellar remnants of stars like our Sun, produce these luminous explosions when their cores experience a runaway thermonuclear reaction.

Because Type Ia supernovae shine brighter than whole galaxies, the stellar explosions can be seen from more than 10 billion light years away, which is about three-quarters of the age of the universe.

The apparent brightness of the explosions, which decreases with distance, and redshift measurements can be used by astronomers as indicators of time and location because supernovae have essentially uniform intrinsic brightnesses.

This information, in turn, indicates the rate at which the cosmos expands during different epochs, which is subsequently utilized to test theories on the fundamental components of the universe.

By looking at Type Ia supernovae in this way, scientists found out for the first time in 1998 that the universe is growing faster than they thought.

The universe’s fabric contains an unobservable energy known as dark energy, which scientists believe is responsible for the expansion.

Subsequent decades of investigation have accumulated ever-larger datasets, exposing supernovae throughout an even broader range of space and time; Pantheon+ has now compiled them into the most statistically robust analysis to date.

Adam Riess, 2011 Nobel Prize in Physics, says that in many ways the most recent Pantheon+ analysis is the culmination of more than two decades’ worth of diligent work by observers and theorists worldwide in understanding the essence of the cosmos.

Scolnic created the original Pantheon analysis of around 1,000 supernovae several years ago.

Now, with the help of the new Pantheon+ team led by Brout and Scolnic, we have double the precision of the original Pantheon thanks to the addition of almost 50 percent more data points on supernovae and advancements in analytical methodologies and the elimination of potential sources of mistake.

“This leap in both the dataset quality and in our understanding of the physics that underpin it would not have been possible without a stellar team of students and collaborators working diligently to improve every facet of the analysis,” Brout adds.

Looking at the big picture, the new research concludes that dark energy accounts for 66.2% of the universe and that dark matter and energy make up the other 33.8%.

Brout and colleagues combined Pantheon+ with additional well-supported, independent, and complementary measurements of the large-scale structure of the universe as well as with measurements from the cosmic microwave background, the universe’s first light source, to reach an even more thorough understanding of the constituent parts of the universe at various epochs.

One of the most important aims of contemporary cosmology is to determine the precise value of the Hubble constant, which measures the rate at which the universe is expanding at the present time.

The Pantheon+ sample is combined with data from the SH0ES (Supernova H0 for the Equation of State) project, led by Riess, to produce the most accurate local measurement of the universe’s current expansion rate.

With only 1.3% uncertainty, Pantheon+ and SH0ES jointly determine the Hubble constant to be 73.4 km/s/Mp. Or, to put it another way, the research predicts that the expansion of space in the nearest universe is happening at a rate of more than 160,000 miles per hour for every megaparsec, or 3.26 million light years.

But evidence from a very different period in the history of the cosmos suggest a different story.

When combined with the current Standard Model of Cosmology, measurements of the cosmic microwave background, which is the oldest light in the universe, always put the Hubble constant at a rate that is much slower than what has been seen with Type Ia supernovae and other astrophysical markers.

The Hubble tension refers to this substantial difference between the two methodologies.

This Hubble conflict is exacerbated by the latest Pantheon+ and SH0ES datasets. In reality, the tension has already surpassed the crucial 5-sigma threshold, which physicists use to distinguish between potential statistical flukes and something that has to be understood. This threshold refers to the probability of anything occurring by chance of occurring once in a million events.

Reaching this new statistical threshold emphasizes how difficult it is for astronomers and theorists to come up with an explanation for the Hubble constant gap.

We thought it would be possible to find clues to a novel solution to these problems in our dataset, but instead we’re finding that our data rules out many of these options and that the profound discrepancies remain as stubborn as ever,” adds Brout. 

The Pantheon+ findings might help to identify the location of the Hubble tension fix. However, such unproven theories must resist the scientific process, and the Hubble tension continues to be a huge barrier, according to Brout. “Many recent theories have begun pointing to exotic new physics in the very early universe.”

For researchers, Pantheon+ is a window into a vast swath of cosmic history. The dataset’s oldest and farthest supernovae shine from a distance of 10.7 billion light years, which corresponds to a time when the universe was around 25% older than it is now.

Dark matter and the gravitational pull it produced during that earlier period controlled the universe’s rate of expansion. Over the next few billion years, this situation drastically changed when dark energy’s influence overpowered that of dark matter.

Since then, dark energy has pushed everything farther apart and at a faster and faster rate.

Using the merged Pantheon+ dataset, Brout claims that “we get a precise view of the universe from the time when it was dominated by dark matter to when the universe became dominated by dark energy. This dataset is a unique opportunity to see dark energy turn on and drive the evolution of the cosmos on the grandest scales up through present time.”

It is hoped that studying this switch now, with even stronger statistical evidence, would provide new insights into the mysterious nature of dark energy.

“Pantheon+ is giving us our best chance to date of constraining dark energy, its origins, and its evolution,” adds Brout.

Image Credit: NASA/CXC/U.Texas

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