Fast Radio Bursts offer new way to map the universe's ordinary matter

Researchers from Caltech and other institutions have demonstrated that Fast Radio Bursts (FRBs) can be used to map the distribution of ordinary matter across the universe. The findings, published in Nature Astronomy, suggest these high-energy signals provide a new way to resolve long-standing mysteries regarding the composition and expansion of the cosmos.

By analyzing a sample of approximately 100 FRBs, the research team measured the impact of galactic feedback—the process where supermassive black holes and exploding stars eject gas into space. This feedback smooths out the distribution of cosmic matter. Because FRB signals disperse as they travel through matter, acting similarly to how a prism splits light, they serve as effective tracers for baryons, or ordinary matter. According to the study, this represents the first time scientists have used FRBs to directly measure how galactic feedback affects clumpy matter in the vast regions between galaxies.

The challenge of cosmic noise

Cosmologists traditionally rely on sky surveys to map how matter clumps together, which helps them understand the nature of dark matter, the mass of neutrinos, and dark energy—the force driving the universe's expansion. However, the data from X-ray and microwave surveys has historically been muddied by galactic feedback. Because the smoothing effect of ejected gas mimics the signals produced by neutrinos or dark energy, it has been difficult for researchers to determine which force is responsible for the observed distribution of matter.

Cleaning the cosmological record

This new capability allows scientists to independently measure the contribution of galactic feedback, effectively "cleaning" cosmological data. By isolating the noise created by black holes and supernovae, researchers can more precisely measure the fundamental properties of the universe. This distinction is critical for understanding how large-scale galactic structures formed and for refining current models of dark energy and neutrino mass.

The road to 2029

While current results are based on a small sample, the potential for growth is significant. Elisabeth Krause, a professor of astronomy and physics at The University of Arizona, noted that the analysis delivered constraints competitive with X-ray and microwave surveys despite using only 100 FRBs, stating that "it's only the beginning."

To scale these observations, Caltech is developing the Deep Synoptic Array (DSA) in Nevada. Scheduled for completion by 2029, the DSA is expected to detect tens of thousands of FRBs. Vikram Ravi, a professor of astronomy at Caltech, described the upcoming array as a "game changer for the field," promising a massive increase in the data available to map the invisible architecture of the universe.