Galaxies are distributed throughout the universe as a complex network of nodes connected by filaments, which are thus separated by voids. This is known as the cosmic web.
The fibers are thought to contain almost all of the ordinary (so-called baryonic) matter of the universe as a diffuse, hot gas. Nonetheless, the signal emitted by this diffuse gas is feeble to the point that, in reality, 40 to 50% of the baryons go undetected.
These missing baryons are hidden in the filamentary structure of the cosmic web.
Nabila Aghanim, a researcher at the Institut d’Astrophysique Spatiale (CNRS/Université Paris-Saclay), and Hideki Tanimura, a post-doctoral researcher, together with their colleagues, are attempting to detect them. In fact, in a new study, they presented a statistical analysis that reveals, for the first time, the X-ray emission from the hot baryons in filaments.
The team used the spatial correlation between the filaments’ position and the associated X-ray emission to provide evidence of the presence of hot gas in the cosmic web and measure its temperature for the first time. The detection was 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 survey.
These findings confirm earlier analyses by the same research team, based on indirect detection of hot gas in the cosmic web through its effect on the cosmic microwave background. This paves the way for more detailed studies, using better quality data, to test the evolution of gas in the cosmic web’s filamentary structure.
- H. T Tanimura et al. First detection of stacked X-ray emission from cosmic web filaments, Astronomy & Astrophysics (2020). DOI: 10.1051/0004-6361/202038521