Has the hidden matter of the universe been discovered? – ScienceDaily


Astrophysicists believe 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 / Universit√© 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 in reality 40-50% of the baryons[1] goes unnoticed.

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 / Universit√© 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 ROSAT[2] survey data, from approximately 15,000 large-scale cosmic filaments identified in the SDSS[3] galaxy survey. 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.[4]. 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.


1 Baryons are particles made up of three quarks, such as protons and neutrons. They make up atoms and molecules as well as all the structures that can be seen in the observable Universe (stars, galaxies, clusters of galaxies, etc.). The hitherto undetected “missing” baryons should not be confused with dark matter, which is made up of non-baryon matter of unknown nature.

2 ROSAT was a German space telescope designed for X-ray observation.

3 The Sloan Digital Sky Survey (SDSS) is a program for detecting celestial objects using a 2.5 meter dedicated optical telescope located at the Apache Point Observatory (New Mexico, USA). It started collecting data in 2000.

4 See the article: Density and temperature of the filaments of the cosmic network on scales of tens of megaparsecs, Tanimura, H .; Aghanim, N.; Bonjean, V .; Malavasi, N.; Douspis, M. Astronomy and astrophysics, Volume 637, A41 (2020).

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