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Where Are All the Baryons?

7 Feb 2020, 03:05 UTC
Where Are All the Baryons?
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Title: Probing the missing baryons with the Sunyaev-Zel’dovich effect from filamentsAuthors: Anna de Graaff, Yan-Chuan Cai, Catherine Heyman, and John A. PeacockFirst Author’s Institution: Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh, UK; Leiden Observatory, Leiden University, Leiden, The NetherlandsStatus: Published in Astronomy & Astrophysics, open access on arXiv

The Missing Baryon Problem

All of the material we see around us is made up of atoms, also known as baryonic matter. From studies of Big Bang Nucleosynthesis and the Cosmic Microwave Background (CMB), we know that baryons make up only 5% of the Universe. The rest is made of still largely unknown forms of matter and energy we call dark matter and dark energy. We have a problem though with the 5% of the Universe we know about: we don’t know where all the baryons are.

Baryons in galaxies and galaxy clusters make up only ~20% of all baryons in the Universe. The existence of another ~30% of the baryons can be inferred from the Lyman-alpha forest. Cosmological simulations suggest that the rest of the baryons (roughly 50%) reside in the WHIM (warm-hot intergalactic medium). The WHIM is composed of filaments and sheets of warm-hot gas that ...

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