Astronomers using fast radio bursts have directly detected the universe’s missing ordinary matter for the first time.
For decades, cosmologists faced a glaring cosmic discrepancy. While measurements of the early universe indicated that about 17 percent of all matter should be ordinary baryonic matter—everything from stars and planets to human bodies—the total mass of all observed stars, galaxies, and galactic clouds accounted for only a fraction of that amount. The rest remained stubbornly unaccounted for, earning the designation of the missing baryon problem. Unlike dark matter, which does not interact with light, this normal matter was simply spread too thinly across the cosmos to see. Now, a team of researchers has resolved that puzzle by mapping the universe’s hidden mass.
Using Fast Radio Bursts as Cosmic Backlights
To locate the elusive material, astronomers turned to fast radio bursts, which are ultrabright millisecond flashes of radio waves originating from distant galaxies. As these high-energy signals travel across billions of light-years to reach Earth, the light passes through cosmic gas and gets stretched or smeared in time. By measuring this dispersion precisely, scientists can determine the density of the matter along the signal’s path. Researchers analyzed 69 localized fast radio bursts originating from distances ranging from about 11.7 million to roughly 9.1 billion light-years away, allowing them to use the flashes as FAB searchlights for missing matter.
Among the analyzed signals was FRB 20230521B, which now holds the record for the most distant FRB ever recorded at approximately 9.1 billion light-years away. Pinpointing the exact origins of these distant signals required specialized instruments, including the Deep Synoptic Array-110 network of radio telescopes located at MIT. Researchers combined these radio detections with distance measurements from Hawaii’s W. M. Keck Observatory and the Palomar Observatory near San Diego, alongside data from the Australian Square Kilometre Array Pathfinder.
Mapping the Cosmic Distribution of Baryonic Matter
The methodology yielded a comprehensive inventory of where ordinary matter actually resides. The results confirmed that approximately 76 percent of the universe’s normal matter lurks within the intergalactic medium, floating in the vast spaces between galaxies.
If you see a person in front of you, you can find out a lot about them.
But if you just see their shadow, you still know that they’re there and roughly how big they are,
Ravi explained regarding the baryon shadow technique.
Tracing Galaxy Growth and Violent Feedback Processes
Separate analyses focusing on the spatial arrangement of the matter revealed that diffuse clouds of gas extend much further out from galaxies than previously modeled. Researchers noted that these clouds tend to be denser in regions with higher concentrations of neighboring galaxies.
This wider distribution indicates that energetic phenomena within galaxies—such as black hole jets and exploding stars—are far more violent than scientists previously recognized. These cosmic mechanisms act like a thermostat, blasting gas completely out of galaxies and pushing matter far into the intergalactic medium.
Next-Generation Telescopes and Open Cosmological Questions
With the decades-old missing baryon problem largely settled, astronomers are turning their attention toward future capabilities that will expand on these findings.
