In the vast expanses of the universe, ordinary matter—the stuff stars, planets, and we are made of—has long puzzled astronomers. Theoretical calculations based on the Big Bang predicted a certain amount of baryons (protons and neutrons). However, when observed with telescopes, a significant portion of this matter seemed to disappear. Where was it hiding? The answer came thanks to mysterious and powerful radio bursts—fast radio bursts, or FRBs.
Researchers used nearly 3,000 radio bursts to trace invisible plasma around galaxies and found that gas extended much farther than expected — reshaping our picture of how the universe’s “missing” matter is dispersed. Read the paper in @physrevlett: go.aps.org/4fvrutf
These short, bright pulses of radio emission, lasting only milliseconds, originate in distant galaxies. They travel billions of light-years, passing through tenuous plasma—ionized gas. Along the way, the signals disperse: lower frequencies are delayed more than higher frequencies. The more free electrons in the path, the greater the 'smearing.' This effect has become the perfect tool for 'weighing' invisible matter.
The international CHIME/FRB collaboration, which includes scientists from MIT, McGill, and other institutions, analyzed nearly 3,000 such bursts from the second CHIME telescope catalog. They correlated dispersion data with the positions of millions of galaxies from the DESI Legacy Imaging Survey. The results, published in Physical Review Letters, were impressive.
It turned out that the 'missing' baryons are concentrated not only in the intergalactic medium (IGM) but also in vast, diffuse clouds around the galaxies themselves—the so-called circumgalactic medium (CGM). The gas extends much farther than expected, up to about 4 million light-years from the galaxies, which is tens of times the size of a typical galaxy. Where there are more galaxies, there is also more matter around them. This suggests that galaxies actively 'eject' gas outward through processes like jets from supermassive black holes and supernova explosions.
Imagine: a galaxy is not a closed system but a fountain, which fountains matter into the surrounding space. Previously, simulations predicted a more compact distribution, but reality turned out to be different—the gas forms enormous 'fluffy' clouds. This changes our understanding of galaxy evolution and the cosmic web as a whole.
The work not only solves the long-standing missing baryons puzzle but also demonstrates the power of a new method. FRBs act as cosmic probes, illuminating the invisible regions of the universe. With the increasing number of detected bursts (and there are thousands per day), astronomers will be able to map the distribution of matter even more precisely and test models of the large-scale structure of the cosmos.
This research is a prime example of how unexpected phenomena like FRBs transform from a puzzle into a powerful tool. What else is hidden within these millisecond flashes will be revealed by future observations. The cosmos is gradually revealing its secrets, one radio burst at a time.
