Artist’s impression of two white dwarf stars merging to create a Type Ia supernova. Credits: ESO/L. in calcada
More than two decades of analysis of supernova explosions convincingly strengthens modern cosmological theories and invigorates efforts to answer fundamental questions.
A powerful new analysis has been done by astrophysicists that puts the most precise limits ever on the composition and evolution of the universe. With this analysis, called Pantheon+, cosmologists find themselves at a crossroads.
Pantheon+ convincingly finds that about two-thirds of the cosmos is made up of dark energy and one-third of matter – predominantly in the form of dark matter – and has been expanding at an accelerating rate over the past few billion years. However, Pantheon+ also reinforces a major disagreement over the speed of this expansion, which has yet to be resolved.
By placing dominant modern cosmological theories, known as the Standard Model of Cosmology, on even more solid evidence-based and statistical foundations, Pantheon+ dark energy and dark matter. Both are cornerstones of the Standard Cosmology Model, but have yet to be directly identified. They are among the biggest mysteries of the model. Researchers following the results of Pantheon+ can now perform more precise observational tests and provide clearer explanations for the apparent cosmos.
G299 was overtaken by a particular class of supernovae called Type Ia. Credit: NASA/CXC/U.Texas
“With these Pantheon+ results, we are able to place the most precise constraints ever on the dynamics and history of the universe,” says Dillon Brout, an Einstein Fellow at the Center for Astrophysics. Harvard and Smithsonian. “We’ve combed through the data and now we can say with more confidence than ever that how the universe has evolved over the ages and that the best theories available for dark energy and dark matter are strong.”
Brout is the lead author of a series of articles describing the new situation. Pantheon+ analysisCo-published in a special issue on October 19, Astrophysical Journal.
Pantheon+ is based on the largest dataset of its kind, containing more than 1,500 stellar explosions called Type Ia supernovae. These bright bursts occur when:[{” attribute=””>white dwarf stars — remnants of stars like our Sun — accumulate too much mass and undergo a runaway thermonuclear reaction. Because Type Ia supernovae outshine entire galaxies, the stellar detonations can be glimpsed at distances exceeding 10 billion light years, or back through about three-quarters of the universe’s total age. Given that the supernovae blaze with nearly uniform intrinsic brightnesses, scientists can use the explosions’ apparent brightness, which diminishes with distance, along with redshift measurements as markers of time and space. That information, in turn, reveals how fast the universe expands during different epochs, which is then used to test theories of the fundamental components of the universe.
The breakthrough discovery of the accelerating growth of the universe in 1998 was thus thanks to the study of a Type Ia supernova. Scientists attribute the expansion to an invisible energy unique to the very fabric of the universe, hence dark energy. Subsequent decades of work continued to compile larger datasets revealing supernovae over an even wider range of space and time, and Pantheon+ has now brought them together in the most statistically robust analysis to date.
“In many ways, this latest Pantheon+ analysis is the result of more than two decades of diligent efforts by observers and theorists around the world to decipher the essence of the cosmos,” says Adam Riess, one of the 2011 Nobel Prize winners. Bloomberg Distinguished Professor of Physics and Bloomberg for the discovery of the accelerating expansion of the universe Johns Hopkins University (JHU) and Space Telescope Science Institute in Baltimore, Maryland. Riess is also a Harvard University graduate and holds a PhD in astrophysics.
“With this combined Pantheon+ dataset, we get a precise view of the universe from when the universe was dominated by dark matter to when the universe was dominated by dark energy.” – dillon brout
Brout’s own career in cosmology goes back to his undergraduate years at JHU, where he taught and advised by Riess. There, Brout worked with Riess advisor Dan Scolnic, who was then a doctoral student and is now an assistant professor of physics at Duke University and is another co-author on the new paper series.
A few years ago, Scolnic developed the original Pantheon analysis of nearly 1,000 supernovae.
Now, Brout and Scolnic and their new Pantheon+ team have added nearly 50 percent more supernova data points to Pantheon+, combined with improvements in analysis techniques and addressing potential sources of error, resulting in twice the precision of the original Pantheon.
“This leap in both dataset quality and our understanding of the physics that underpins it wouldn’t have been possible without a star team of students and collaborators working diligently to improve every aspect of analysis,” says Brout.
Taking the data as a whole, the new analysis shows that 66.2 percent of the universe manifests as dark energy, and the remaining 33.8 percent is a combination of dark matter and matter. To achieve a more comprehensive understanding of the constituent components of the universe in different epochs, Brout and colleagues combined Pantheon+ with strongly proven, independent and complementary measurements of the large-scale structure of the universe and measurements from the earliest light. universe, cosmic microwave background.
“With these Pantheon+ results, we are able to place the most precise constraints ever on the dynamics and history of the universe.” – dillon brout
Another important Pantheon+ result relates to one of the most important goals of modern cosmology: determining the current rate of expansion of the universe, known as the Hubble constant. Combining the Pantheon+ sample with data from the Riess-led SH0ES (Supernova H0 for State Equation) collaboration results in the most stringent local measurement of the universe’s current expansion rate.
Together, Pantheon+ and SH0ES find a Hubble constant of 73.4 kilometers per second per megaparsec with an uncertainty of only 1.3%. In other words, for every megaparsec, or 3.26 million light-years, the analysis estimates that in the nearby universe space itself is expanding at more than 160,000 miles per hour.
However, observations from an entirely different period in the universe’s history predict a different story. Measurements of the universe’s oldest light, the cosmic microwave background, when combined with the current Standard Cosmology Model, hold the Hubble constant at a significantly lower rate than observations made through Type Ia supernovas and other astrophysical markers. This major difference between the two methodologies has been termed the Hubble tension.
The new Pantheon+ and SH0ES datasets add to this Hubble tension. In fact, the voltage crossed the important 5 sigma threshold (about one in a million probability of occurrence due to random chance) that physicists use to distinguish between possible statistical bad luck and something that needs to be understood accordingly. Reaching this new statistical level underscores the challenge for both theorists and astrophysicists to try and explain the Hubble constant inconsistency.
“We thought it would be possible to find clues to a new solution to these problems in our dataset, but instead we find that our data excludes many of these options and that the deep differences are as stubborn as ever,” says Brout. .
The Pantheon+ results can help show where the solution to the Hubble voltage lies. “Many new theories are starting to point to exotic new physics in the very early universe, but such unconfirmed theories need to be based on the scientific process, and the Hubble tension remains a major challenge,” says Brout.
Overall, Pantheon+ offers scientists a comprehensive look at much of cosmic history. The oldest, most distant supernova in the dataset is glowing from 10.7 billion light-years away, when the universe was roughly a quarter of its current age. In that early age, dark matter and its associated gravity controlled the rate of expansion of the universe. Such a situation changed dramatically over the next few billion years, as the effect of dark energy suppressed the effect of dark matter. Dark energy has since hurled the contents of the cosmos farther and at an ever-increasing speed than ever before.
“With this combined Pantheon+ dataset, we get a precise view of the universe from when dark matter dominated to when the universe was dominated by dark energy,” says Brout. “This dataset is a unique opportunity to see dark energy kick off and advance the evolution of the cosmos at the largest scales ever.”
Examining this shift now with stronger statistical evidence will hopefully lead to new insights into the enigmatic nature of dark energy.
“Pantheon+ gives us the best chance to constrain dark energy, its origins and evolution,” says Brout.
Reference: “The Pantheon+ Analysis: Cosmological Constraints”, Dillon Brout, Dan Scolnic, Brodie Popovic, Adam G. Riess, Anthony Carr, Joe Zuntz, Rick Kessler, Tamara M. Davis, Samuel Hinton, David Jones, W. D’Arcy Kenworthy, Erik R. Peterson, Khaled Said, Georgie Taylor, Noor Ali, Patrick Armstrong, Pranav Charvu, Arianna Dwomoh, Cole Meldorf, Antonella Palmese, Helen Qu, Benjamin M. Rose, Bruno Sanchez, Christopher W. Stubbs, Maria Vincenzi, Charlotte M. Wood, Peter J. Brown, Rebecca Chen, Ken Chambers, David A. Coulter, Mi Dai, Georgios Dimitriadis, Alexei V. Filippenko, Ryan J. Foley, Saurabh W. Jha, Lisa Kelsey, Robert P. Kirshner, Anais Möller, Jessie Muir, Seshadri Nadathur, Yen-Chen Pan, Armin Rest, Cesar Rojas-Bravo, Masao Sako, Matthew R. Siebert, Mat Smith, Benjamin E. Stahl and Phil Wiseman, 19 October 2022 Astrophysical Journal.
DOI: 10.3847/1538-4357/ac8e04
