Missing Matter in Universe Found

Summary

The vast majority of matter in the universe is dark—it is entirely invisible and detected only through its gravitational effects. Ordinary matter—everything from protons to planets to people—makes up only 16 percent. Unlike dark matter, ordinary matter emits light of various wavelengths and thus can be seen. But a large chunk of it is diffuse and spread thinly among halos that surround galaxies as well as in the vast spaces between galaxies.Due to its diffuse nature, roughly half of ordinary matter in the universe went unaccounted for and had been considered "missing"—until now.In a new study in Nature Astronomy, a team of astronomers at Caltech and the Center for Astrophysics | Harvard & Smithsonian (CfA) has, for the first time, directly detected and accounted for all the missing matter. To do this, the team used brief, bright radio flashes in the distant cosmos, called fast radio bursts (FRBs), to illuminate the matter lying between the FRBs and us."The FRBs shine through the fog of the intergalactic medium, and by precisely measuring how the light slows down, we can weigh that fog, even when it's too faint to see," says Liam Connor, assistant professor at Harvard and lead author of the study, who performed much of the work while a Caltech research assistant professor working with Vikram Ravi, assistant professor of astronomy at Caltech.The study looked at a total of 69 FRBs located at distances ranging from about 11.74 million to about 9.1 billion light-years away. The object 9.1 billion light-years away, named FRB 20230521B, now holds the record for the most distant FRB ever recorded. While more than a thousand FRBs have been detected, only about a hundred have been pinpointed to specific host galaxies; in other words, their origins and distances from Earth are known. These localized FRBs were needed for the current study.Of the 69 localized FRBs in the study, 39 were found using the DSA (Deep Synoptic Array)-110, a National Science Foundation (NSF)-funded netw...