宇宙の「失われた物質」の発見(Missing Matter in Universe Found)

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2025-06-16 カリフォルニア工科大学 (Caltech)

Caltechとハーバード・スミソニアンの研究者らは、宇宙の“失われた”通常物質(バリオン)の所在を高速電波バースト(FRB)を用いて特定。69例のFRBから波長ごとの伝播遅延を解析し、宇宙空間のプラズマ量を測定。結果、通常物質の76%が銀河間空間、15%がハロー領域、9%が銀河内部に存在することが判明。長年の天文学的課題に解を与えた。成果は『Nature Astronomy』に掲載。

<関連情報>

失われた重粒子の分割によって明らかになったガスに富む宇宙網 A gas-rich cosmic web revealed by the partitioning of the missing baryons

Liam Connor,Vikram Ravi,Kritti Sharma,Stella Koch Ocker,Jakob Faber,Gregg Hallinan,Charlie Harnach,Greg Hellbourg,Rick Hobbs,David Hodge,Mark Hodges,Nikita Kosogorov,James Lamb,Casey Law,Paul Rasmussen,Myles Sherman,Jean Somalwar,Sander Weinreb,David Woody & Ralf M. Konietzka
Nature Astronomy  Published:16 June 2025
DOI:https://doi.org/10.1038/s41550-025-02566-y

宇宙の「失われた物質」の発見(Missing Matter in Universe Found)

Abstract

Approximately half of the Universe’s dark matter resides in collapsed halos; significantly less than half of the baryonic matter (protons and neutrons) remains confined to halos. A small fraction of baryons are in stars and the interstellar medium within galaxies. The majority are diffuse (<10−3 cm−3) and ionized (neutral fraction <10−4), located in the intergalactic medium (IGM) and in the halos of galaxy clusters, groups and galaxies. This diffuse ionized gas is notoriously difficult to measure, but has wide implications for galaxy formation, astrophysical feedback and precision cosmology. Recently, the dispersion of extragalactic fast radio bursts (FRBs) has been used to measure the total content of cosmic baryons. Here we present a large cosmological sample of FRB sources localized to their host galaxies. We have robustly partitioned the missing baryons into the IGM, galaxy clusters and galaxies, providing a late-Universe measurement of the cosmic baryon abundance, Ωbh70=0.051+0.006−0.006, where Ωb is the baryon density parameter and h70 is the scaled Hubble constant. Our results indicate efficient feedback processes that can deplete galaxy halos and enrich the IGM (total baryon fraction in the IGM is fIGM=0.76+0.10−0.11), agreeing with the baryon-rich cosmic web scenario seen in cosmological simulations. Our results may reduce the ‘S8 tension’ in cosmology, as strong feedback leads to suppression of the matter power spectrum.

1701物理及び化学
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