Scientists locate universe’s ‘missing’ matter in vast clouds around galaxies

Astronomers have pinpointed the location of the universe's long-sought "missing" ordinary matter, finding it scattered in vast, diffuse clouds stretching millions of light-years from galaxies — far further than simulations had predicted.

A New Cosmic Census

In a study published in Physical Review Letters, researchers from the CHIME/Fast Radio Bursts Collaboration developed a method that cross-references thousands of fast radio burst detections with the mapped positions of millions of galaxies. The team, led by Haochen Wang, a graduate student at MIT's Kavli Institute for Astrophysics and Space Research, and Kiyoshi Masui, an associate professor of physics at MIT, analyzed 2,870 FRB signals captured by the CHIME radio telescope in British Columbia. They then compared the data with the locations of over six million galaxies cataloged by the Dark Energy Spectroscopic Instrument (DESI) at Kitt Peak National Observatory in Arizona.sflorg+1

The technique relies on a property of fast radio bursts: as these millisecond flashes of radio waves travel through space, they become "smeared" by the matter they pass through. Lower-energy wavelengths are delayed more than higher-energy ones, and by measuring the degree of smearing, researchers can calculate precisely how much matter each burst encountered on its journey to Earth.miragenews+1

Further Than Expected

The analysis revealed that the missing baryonic matter — protons, neutrons, and electrons unaccounted for by stars and galaxies — gathers in diffuse "puffs" surrounding galaxy groups. These clouds extend roughly four million light-years from their host galaxies, well beyond what computer simulations had predicted.sflorg+1

"A galaxy is maybe a few 100,000 light-years across, and we found missing matter out to about 4 million light-years," Masui said. "That's further than the simulations predict, by quite a bit."sflorg

The findings suggest that black hole jets, supernovae, and other energetic galactic processes expel gas with far greater force than researchers had assumed. "We are finding that the activity in galaxies is messier than we thought," Wang said. "They're more like fountains, and really push out gas to very large distances."sflorg

A Scalable Tool

Victoria Kaspi, a professor of physics at McGill University and study co-author, called fast radio bursts "amazingly effective in probing the distribution of matter in the universe." With CHIME having detected roughly 4,000 FRBs since it began observations, the team expects the method to grow more precise as additional data accumulates. "We got it to work for the first time, and will get it to work even more precisely as data gets better," Masui said.miragenews