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Physicists open a new window into the dark energy

Cluster galaxy density map

A map of the sky showing the density of galactic clusters, galaxies, and matter in the universe above the part of the sky observed by the Dark Energy Study. The left panel shows the density of the galaxy in this part of the sky, while the middle panel shows the density of matter, and the right panel shows the density of the clusters of galaxies. The red areas are denser and the blue areas are less dense than the middle ones. Credit: Chun-Hao To / Stanford University, SLAC National Accelerator Laboratory

For the first time, DES scientists can combine measurements of the distribution of matter, galaxies and galactic clusters to improve our understanding of dark energy.

The universe is expanding at an ever-increasing rate, and while no one is sure why, Dark Energy Research (DES) researchers have at least had a strategy for doing so: They will combine measurements of the distribution of matter, galaxies, and galaxy clusters to understand better what happens.

Achieving this goal turned out to be quite complicated, but now a team led by researchers from the National SLAC Accelerator Laboratory of the Department of Energy, Stanford University and the University of Arizona has found a solution. Their analysis, published recently in Physical examination letters, gives more accurate estimates of the average density of matter, as well as its tendency to collect – two key parameters that help physicists study the nature of dark matter and dark energy, the mysterious substances that make up the vast majority of the universe.

“This is one of the best limitations of one of the best datasets to date,” said Chun-Hao To, lead author of the new paper and a graduate student at SLAC and Stanford, working with Kavli, director of particle astrophysics and cosmology. Risa Wechsler.

Early goal

When DES set out in 2013 to map the eighth from the sky, the goal was to collect four types of data: distances to certain types of supernovae or exploding stars; the distribution of matter in the universe; the distribution of galaxies; and the distribution of galactic clusters. Everyone tells researchers something about how the universe evolved over time.

Ideally, scientists would gather all four data sources to improve their estimates, but there is a problem: The distribution of matter, galaxies, and galactic clusters are closely linked. If researchers do not take these relationships into account, they will eventually get “double counting”, giving too much weight to some data and not enough weight to others, It says.

To avoid mishandling all this information, To, University of Arizona astrophysicist Elizabeth Krause and colleagues have developed a new model that can correctly account for relationships in the distributions of all three quantities: matter, galaxies, and galactic clusters. In this way, they were able to make a first-of-its-kind analysis to properly combine all of these diverse datasets to learn about dark matter and dark energy.

Improving estimates

Adding this model to DES analysis has two effects, It says. First, measurements of the distribution of matter, galaxies, and galactic clusters tend to introduce different types of errors. Combining the three measurements makes it easier to identify such errors, making the analysis more reliable. Second, the three measurements differ in how sensitive they are to the average density of matter and its stiffness. As a result, combining all three can improve the precision with which DES can measure dark matter and dark energy.

In the new report, To, Krause and colleagues apply their new methods for the first year of DES data and sharpen the accuracy of previous estimates of matter density and stiffness.

Now that the team can include matter, galaxies and galactic clusters simultaneously in its analysis, adding supernova data will be relatively simple, as this type of data is not as closely related to the other three, It said.

“The immediate next step,” he says, “is to apply the machine to DES 3’s data, which has three times the coverage of the sky.” It’s not as simple as it sounds: Although the basic idea is the same , the new data will require extra effort to improve the model to keep up with the higher quality of the newer data, it says.

“This analysis is really exciting,” Wechsler said. “I expect it to set a new standard in the way we can analyze data and learn about dark energy from large studies, not only about DES, but also look forward to the incredible data we get from the Vera Rubin’s Legacy Survey.” of space and time in a few years. “

Reference: “Results of the 1st year dark energy study: Cosmological constraints from cluster abundance, weak objectification, and galactic correlations” by C. To et al. (DES Collaboration), April 6, 2021, Physical examination letters.
DOI: 10.1103 / PhysRevLett.126.141301

The study was a joint effort within the Dark Energy Study and was supported by the National Science Foundation and the Ministry of Science of the Ministry of Energy.

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