Unveiling the Universe’s Missing Matter: A Breakthrough Using Fast Radio Bursts

A significant discovery in cosmology has pinpointed the location of the universe’s “missing” baryonic matter. Researchers from the Center for Astrophysics | Harvard & Smithsonian (CfA) and the California Institute of Technology, publishing their findings in Nature Astronomy, have revealed that over three-quarters of ordinary matter resides in the diffuse gas filaments between galaxies.

For years, astronomers have grappled with the “missing baryon problem,” a significant discrepancy between the predicted amount of ordinary matter and what could be directly observed. This ordinary matter, primarily composed of protons, was theorized to exist as a hot, low-density gas within the intergalactic medium (IGM). However, its detection proved elusive using traditional astronomical methods.

This groundbreaking study leveraged the unique properties of Fast Radio Bursts (FRBs) – intense, brief bursts of radio waves originating from distant galaxies. By analyzing the dispersion—the slowing down of radio waves as they traverse space—of 69 FRBs spanning distances from 11.74 million to a record-breaking 9.1 billion light-years, the team meticulously mapped the distribution of this elusive matter.

Their analysis concluded that approximately 76% of the universe’s ordinary matter is situated in the IGM. This aligns remarkably well with predictions from sophisticated cosmological simulations. The remaining baryonic matter is distributed between galaxy halos (15%) and within stars or cold galactic gas (9%).

“It’s a triumph of modern astronomy,” commented Vikram Ravi, an assistant professor of astronomy at Caltech and a co-author of the paper. The implications of this discovery are far-reaching, offering crucial insights into galaxy formation, the large-scale structure of the universe, and the propagation of light across cosmological distances.

Liam Connor, an astronomer at CfA and lead author of the study, highlighted the dynamic interplay between galaxies and the IGM: “Baryons are pulled into galaxies by gravity, but supermassive black holes and exploding stars can blow them back out. Our results show this feedback must be efficient, blasting gas out of galaxies and into the IGM.” This finding provides valuable constraints on models of galactic evolution and the feedback mechanisms driving the distribution of matter in the universe.

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