Hidden Baryons: Astronomers Locate Half the Universe’s Ordinary Matter in Diffuse Galactic Gas

Astronomers stacked millions of galaxies and used the cosmic microwave background as a backlight to detect very diffuse ionized hydrogen gas around mature galaxies via the kinematic Sunyaev–Zel’dovich effect, suggesting the universe’s missing ordinary matter is out there and may trace the cosmic web; if confirmed, this finding could reshape understanding of galactic feedback but awaits peer review.