Warm–hot baryons comprise 5–10 per cent of filaments in the cosmic web

Authors:
Open Access
Publisher website
Google Scholar
Abstract
In the local Universe, the census of all observed baryons falls short of the estimated number by a factor of two, and simulations have indicated that the missing baryons reside throughout the filaments of the cosmic web; X-ray observations of filamentary structures associated with the galaxy cluster Abell 2744 now find that 5 to 10 per cent of the filament mass is in the form of baryonic gas. It is estimated that observations of the local Universe, to date, account for about 60% of the baryonic matter — 'ordinary' atoms as opposed to subatomic particles or leptons — that should be present in theory. Numerical simulations indicate that the missing baryons have not yet condensed into gravity-bound halos, but may instead be found in the filaments of the cosmic web, a vast network of dark-matter filaments. Dominique Eckert et al. report X-ray observations of filamentary structures associated with the galaxy cluster Abell 2744. The filaments consist of gas at a temperature of around ten-million-degrees kelvin, extending for 8 megaparsecs. These properties support a picture in which a large fraction of the Universe's baryons are located in the filaments of the cosmic web. Observations of the cosmic microwave background indicate that baryons account for 5 per cent of the Universe’s total energy content1. In the local Universe, the census of all observed baryons falls short of this estimate by a factor of two2,3. Cosmological simulations indicate that the missing baryons have not condensed into virialized haloes, but reside throughout the filaments of the cosmic web (where matter density is larger than average) as a low-density plasma at temperatures of 105−107 kelvin, known as the warm–hot intergalactic medium3,4,5,6. There have been previous claims of the detection of warm–hot baryons along the line of sight to distant blazars7,8,9,10 and of hot gas between interacting clusters11,12,13,14. These observations were, however, unable to trace the large-scale filamentary structure, or to estimate the total amount of warm–hot baryons in a representative volume of the Universe. Here we report X-ray observations of filamentary structures of gas at 107 kelvin associated with the galaxy cluster Abell 2744. Previous observations of this cluster15 were unable to resolve and remove coincidental X-ray point sources. After subtracting these, we find hot gas structures that are coherent over scales of 8 megaparsecs. The filaments coincide with over-densities of galaxies and dark matter, with 5–10 per cent of their mass in baryonic gas. This gas has been heated up by the cluster’s gravitational pull and is now feeding its core. Our findings strengthen evidence for a picture of the Universe in which a large fraction of the missing baryons reside in the filaments of the cosmic web.
Keywords

This publication has 51 references indexed in Scilit: