Researchers present the most accurate map of the distribution of matter in the universe to date

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Using data from a dark energy survey conducted at the Inter-American Observatory in Cerro Tololo, Chile, and the South Pole Telescope located at the Amundsen-Scott Polar Station in Antarctica, a team of scientists has established the most accurate distribution of matter in the universe to date. Their results show that he is not as “bunched” as we think he is in the end.

At the beginning of the universe, 13.7 billion years ago, the first elements that made up matter were contained in a dense and hot environment. This one underwent a strong expansion, scattering elementary particles in all directions. The temperature dropped quickly. Then the first protons and neutrons appeared, then the first nuclei of hydrogen, then helium. Clouds of matter formed little by little, giving rise to the first stars. At their core, successive fusions of light nuclei gave rise to heavier nuclei. Then, when these stars died, their explosion scattered these nuclei throughout the universe.

The process gradually populated the universe with stars, planets and galaxies. A group of scientists decided to follow the entire path of this material; starting from the current state of the universe, they can indeed “go back in time” to determine what happened and what forces contributed to its evolution. To do this, they first had to collect and analyze a huge amount of observational data. This colossal work, which involved more than 150 researchers, is summarized in a series of three papers published in the journal Physical Review D.


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Combination of two observation methods for greater accuracy

The data was provided by two very different telescopes. Dark Energy Exploration (DES) is an international optical and near-infrared research program that aims to map hundreds of millions of galaxies to better understand the nature of dark energy; it is based on the Dark Energy Camera (DECam) installed on the 4-meter Victor M. Blanco Telescope at the Cerro Tololo Inter-American Observatory in Chile. The data is obtained from observation sessions that were conducted from 2013 to 2019.

The South Pole Telescope (SPT) is a 10-meter diameter radio telescope located in Antarctica that probes the cosmic microwave background in search of the very first traces of radiation from the first moments of the universe. It operates in the microwave, millimeter and submillimeter wave bands.

By comparing sky maps based on data from the Dark Energy Survey (left) and data from the South Pole Telescope and the Planck satellite (right), the researchers were able to infer how matter is distributed in the universe. © Yuki Omori

Combining these two sets of data from two different observational methods allows the team to reduce the chance of measurement error — each set serves as a kind of cross-validation against the other, says Chihwei, Chang, an astrophysicist at the University of Chicago. and one of the lead authors of the research.

To estimate the distribution of matter, the team used the phenomenon of gravitational lensing, which refers to the deflection of light caused by the presence of a very massive body, or at least a high concentration of matter (such as a galaxy or cluster of galaxies). ). This method makes it possible to identify ordinary matter… but also mysterious dark matter.

The SPT Collaboration researchers used data from the SPT and the Planck Space Telescope to build an updated map of the gravitational lensing effect of cosmic microwave background photons. The team then matched the map data with DES measurement data showing the position and shape of galaxies, as well as the distribution of matter around them.

The Standard Model of the Universe May Be Incomplete

Noise in the measurements used to determine the cosmological parameters describing the evolution of matter (including the density of dark matter and the expansion rate) can lead to uncertainty in the data and hence inaccuracies in the estimation of these parameters. But cross-analysis of DES and SPT data can reduce these uncertainties. Thus, the “mapping” of matter established by the researchers is even more accurate than previous measurements reported about a year ago.

On the whole, the results are consistent with the currently accepted theory of the evolution of the Universe. But the analysis also reveals several “anomalies” inconsistent with this theory. “It appears that there is a bit less fluctuation in the current universe than we might expect, assuming our standard cosmological model is based on the early universe,” said co-author Eric Baxter, an analyst and astrophysicist at the University of Hawaii.

In other words, if we take into account all currently accepted physical laws, if we take measurements at the beginning of the Universe, and then extrapolate the data, then the results obtained are somewhat different from what can actually be measured in the local Universe. In particular, the team found that the material wasn’t as “sticky” as we expected.

This suggests that something may be missing in the existing model of the Universe. However, further in-depth studies will be required to prove this. Meanwhile, these three studies highlight the benefits of using different astronomical readings to reduce uncertainties. “There are a lot of new things you can do by bringing these different sides of the universe together,” Chang said.


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