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Scientists Identify Missing 15% of Normal Matter in Vast Hydrogen Gas Halos

A new study reveals that diffuse ionized hydrogen gas surrounding galaxies accounts for the universe’s missing baryons, reshaping models of galaxy formation and evolution.

Image
An artist's depiction of the halo of hot hydrogen gas surrounding the Milky Way galaxy (center) and two satellite galaxies, the Large and Small Magellanic Clouds. The halo is more extended that astronomers originally thought, and contains enough hydrogen gas to resolve the problem of the universe's missing baryonic mass. NASA/CXC/M.Weiss; NASA/CXC/Ohio State/A Gupta et al

Overview

  • Researchers used data from DESI and ACT to analyze 7 million galaxies within 8 billion light-years, detecting ionized hydrogen gas via the kinematic Sunyaev-Zel’dovich effect.
  • These diffuse halos of ionized gas extend up to five times farther from galaxies than previously estimated, accounting for the missing 15% of normal matter in the universe.
  • The study suggests that supermassive black holes at galaxy centers eject gas in duty cycles, remaining active beyond early galaxy formation phases.
  • The findings challenge current cosmological models, requiring updates to simulations of galaxy formation and the distribution of matter in the universe.
  • Published as a preprint on arXiv and under peer review for Physical Research Letters, the results represent a major step in resolving the universe’s baryon census.