Has the hidden matter of the universe been discovered?

Astrophysicists consider that about 40% of the ordinary matter that makes up stars, planets and galaxies remains undetected, hidden in the form of hot gas in the complex cosmic web. Today, scientists from the Institut d’Astrophysique Spatiale (CNRS / Université Paris-Saclay) may have detected, for the first time, this hidden matter through an innovative 20-year statistical analysis of data. Their results were published on November 6, 2020 in Astronomy and astrophysics.

Galaxies are distributed throughout the universe in the form of a complex network of nodes connected by filaments, in turn separated by voids. This is known as the cosmic web. The filaments are thought to contain nearly all of the ordinary (so-called baryon) matter in the universe in the form of a diffuse hot gas. However, the signal emitted by this diffuse gas is so weak that 40-50% of the baryons are not actually detected.

These are the missing baryons, hidden in the filamentous structure of the cosmic network, which Nabila Aghanim, researcher at the Institut d’Astrophysique Spatiale (CNRS / Université Paris-Saclay) and Hideki Tanimura, postdoctoral researcher, together with their colleagues. trying to detect. In a new study, funded by the ERC ByoPiC project, they present a statistical analysis that reveals, for the first time, X-ray emission from hot baryons in filaments.

This detection is based on the stacked X-ray signal, in the ROSAT2 survey data, from approximately 15,000 large-scale cosmic filaments identified in the SDSS3 galaxy detection. The team used the spatial correlation between the position of the filaments and the associated X-ray emission to provide evidence for the presence of hot gas in the cosmic network and for the first time to measure its temperature.

These results confirm previous analyzes by the same research group, based on the indirect detection of hot gas in the cosmic network through its effect on the cosmic microwave background. This opens the way for more detailed studies, using better quality data, to test the evolution of gas in the filamentous structure of the cosmic network.