Astronomers Uncover Location of Universe's 'Missing' Ordinary Matter

In a groundbreaking study published on June 16, 2025, in the journal *Nature Astronomy*, astronomers have identified the long-sought ordinary matter that constitutes approximately 15% of the universe. This matter, primarily found as thinly distributed gas in the vast intergalactic medium, has remained elusive despite previous calculations indicating its existence. The research, led by Dr. Liam Connor, a Professor of Astronomy at Harvard University, utilized advanced detection methods involving fast radio bursts (FRBs) from 69 distinct locations across the cosmos to illuminate the whereabouts of this missing matter.

Historically, the understanding of the universe's composition has been marked by a stark contrast between ordinary matter, which includes gas, dust, stars, and planets, and dark matter, an enigmatic substance detectable solely through its gravitational influence. According to the latest findings, about 76% of the ordinary matter is located in intergalactic space, 15% within galaxy halos, and the remaining 9% concentrated in galaxies themselves as stars and gas. As noted by Dr. Connor, “The question we’ve been grappling with was: Where is it hiding? The answer appears to be: in a diffuse wispy cosmic web, well away from galaxies.”

The detection of this ordinary matter relied on the analysis of FRBs, which are powerful pulses of radio waves emitted from distant cosmic events, potentially generated by highly magnetized neutron stars. The study utilized data from the Deep Synoptic Array, a network of 110 radio telescopes at Caltech's Owens Valley Radio Observatory in California, along with other telescopes to capture and analyze the dispersion of radio waves influenced by the presence of matter along their path to Earth.

This significant discovery addresses a pivotal question in astrophysics regarding the location of ordinary matter and its distribution throughout the universe. The research highlighted that vast amounts of gas have been expelled from galaxies through processes such as supernova explosions and the activities of supermassive black holes. Dr. Connor explains, “If the universe were a more boring place, or the laws of physics were different, you might find that ordinary matter would all fall into galaxies... But that’s not what happens.”

The implications of this research extend beyond merely locating ordinary matter; it paves the way for future investigations into the nature of dark matter, which remains one of the greatest mysteries in modern astrophysics. As Dr. Connor emphasized, “We can now move on to even more important mysteries regarding the ordinary matter in the universe, and beyond that: what is the nature of dark matter and why is it so difficult to measure directly?”

This new understanding of ordinary matter's location not only enhances our comprehension of the universe’s structure but also sets the stage for deeper explorations into the fundamental components that govern cosmic dynamics. With the total amount of ordinary matter now accounted for, astronomers are poised to tackle even more complex questions about the universe's composition and the interplay between visible and dark matter.