Fast Radio Bursts (FRB) are one of the cosmos' mysteries. They're transient radio waves that are as short as a fraction of a millisecond or as long as 3 seconds. The first one was detected in 2007, and despite the fact that astronomers have catalogued thousands of them, we don't know what causes them.
Some type of powerful astrophysical event triggers them, but researchers aren't certain. Neutron stars could be responsible, black holes could be, maybe magnetars, maybe aliens. Scientists are still working to understand what causes FRBs.
But even though we don't know their cause, they can still be used to probe one of the cosmos' most perplexing puzzles: the missing mass problem.
Physicists have strong evidence that after the Big Bang, dark matter made up 83% of the Universe's mass. Ordinary, or baryonic matter, made up the remainder. The problem is, we can't find all of the remaining baryonic matter. It seems to be missing.
This is where FRBs come in. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) has found thousands of FRBs, and researchers have a subset of them to search for the missing matter.
Their results are in a paper titled "Measurement of the Dispersion-Galaxy Cross-Power Spectrum with the Second CHIME/FRB Catalog." It's published in Physical Review Letters and the lead authors are Haochen Wang, a graduate student in MIT’s Kavli Institute for Astrophysics and Space Research, and Kiyoshi Masui, associate professor of physics at MIT.
FRBs are extremely bright, and in this work, the researchers developed a way to use them to find the missing matter. They combine FRB detections with the locations of galaxies. As FRBs travel through space, baryonic matter affects them. Their signal is stretched or smeared, and the more mass they travel through, the more they're stretched. By measuring the degree of stretching for 2,870 FRBs, and comparing it with the locations of galaxies, the researchers calculated the amount of matter the FRBs passed through. The more smeared it is, the more mass it passed through.
In scientific terms, the stretching is called dispersion, and it's based on how FRBs interact with free electrons rather than bound electrons in neutral atoms. Since most cosmic baryons outside of dense clouds are ionized, the method can measure the diffused gas in and around galaxies, called the intergalactic medium (IGM) and the circumgalactic medium (CGM).
The top panel shows the dispersion measure from the CHIME/FRB Catalog 2. The bottom panel shows bright galaxies from the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Survey. The researchers correlated both to detect missing baryonic matter in the IGM and CGM of the galaxies. Image Credit: Wang and Masui et al. 2026. PRL.
"The dispersion of extragalactic fast radio bursts (FRBs) can serve as a powerful probe of the diffuse plasma between and surrounding galaxies, which contains most of the Universe’s baryons," the researchers write. "Here we present the measurement of the dispersion–galaxy angular cross-power spectrum between 2873 FRBs from the Second CHIME/FRB Catalog and nearly 6 million galaxies from the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Survey."
The work not only showed how much matter was detected, but where it is. The researchers found that it sits in the IGM and CGM.
“We find that, overall, where there are more galaxies, there tends to be more missing matter around them,” said co-lead author Wang in a press release.
These results back up some of the thinking about galaxies and how they eject matter. Powerful jets from supermassive black holes, supernovae explosions, and other extremely energetic events can drive matter out of galaxies. This research not only supports that picture, but it suggests that these mechanisms are more powerful and energetic than thought.
“We’re finding missing matter that is pushed out to larger scales,” says co-lead author Masui. “These measurements indicate that star activity, and activity from black holes, is stronger and much more violent than predicted.”
This screenshot from Illustris TNG shows simulated gas around galaxies. The white dots are galaxies, and blue, green, and yellow represent gas from dense to diffuse. By showing that gas extends further from galaxies than thought, the researchers may have found the missing mass. They've also shown that a galaxy's energetic processes can eject gas to greater distances than thought. Image Credit: Illustris TNG.
Other research has suggested that diffuse gas extends further from galaxies than thought. Similar research also shows that the reach of energetic events inside galaxies extends further beyond galaxies than thought.
"Similar evidence has come from thermal Sunyaev–Zeldovich studies, where gas filaments are found to extend beyond galaxy pairs, and recent kinetic Sunyaev–Zeldovich works that have found evidence for enhanced feedback in the observed baryon density profiles," the authors explain. "Our measurements would seem to be in qualitative agreement with these works," they write, while also noting that interpreting their results requires more work and astrophyscial modelling.
Since this method of detecting diffuse baryonic matter has produced such strong results, it's likely to expand in the future.
"Our Letter demonstrates that FRBs are promising tools to discern the physics of baryonic structure formation and will only become more powerful as FRB surveys expand," the authors write.
Evan Gough is a science-loving guy with no formal education who loves Earth, forests, hiking, and heavy music. He's guided by Carl Sagan's quote: "Understanding is a kind of ecstasy."
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