Image of G299, the remnant of a Type Ia supernova, the type of cosmic explosion that helped develop accurate descriptions of dark energy and dark matter. (Image credit: NASA/CXC/U.Texas)
Both dark energy and dark matter are cornerstones of the Standard Model of cosmology, but have yet to be detected directly, and thus are the model’s biggest mystery. By placing modern cosmological theory (the Standard Model) on a more solid basis of evidence and statistics this time, Pantheon+ is equivalent to closing the door on other alternative models to explain dark energy and dark matter.
Pantheon+ is based on the largest dataset of its kind, including more than 1,500 stellar explosions called Type Ia supernovae. Because Type Ia supernovae outshine entire galaxies, star explosions can be seen from more than 10 billion light-years away. Since supernovae shine with near-uniform brightness, scientists can use the explosion’s apparent brightness (which diminishes with distance) and redshift measurements as markers of time and space. This information, in turn, revealed how fast the universe was expanding at different times.
“In many ways, the latest Pantheon+ analysis is the culmination of more than two decades of hard work by observers and theorists around the world to decipher the nature of the universe,” said Adam Rees, co-winner of the 2011 Nobel Prize in Physics.
The new analysis took the data as a whole and concluded that 66.2% of the universe manifests as dark energy, and the remaining 33.8% is a combination of dark matter and matter.
Another key result from Pantheon+ is the determination of the current expansion rate of the universe, known as the Hubble constant. The study found a Hubble constant of 73.4 (km/s)/Mpc gap with an uncertainty of only 1.3%.
The researchers say that with the Pantheon+ dataset, they can obtain a precise view of the universe from dark matter-dominated to dark-energy-dominated. This is a unique opportunity to see how dark energy turns on and drives the largest evolution in the universe. Now studying this transition with stronger statistical evidence promises new insights into the mysterious nature of dark energy.