The universe's ordinary matter, including stars and galaxies, makes up much of the cosmos' observable material. However, scientists have been grappling with a cosmic conundrum: there should be more. Physicists have good estimates of the universe's matter content shortly after the Big Bang, with approximately 83% comprising invisible dark matter and the rest ordinary matter. Yet, these estimates exceed the amount of ordinary matter seen in stars and galaxies today. Where did all the 'missing' ordinary matter go? Now, MIT scientists, as part of the CHIME/FRB Collaboration, are using distant radio signals to reveal 'missing' matter in the vast space between galaxies. The team developed a new method to search for 'missing' matter by combining galaxy locations with detections of fast radio bursts. A fast radio burst, or FRB, is an ultrabright, millisecond flash of radio waves emitted by extremely energetic phenomena in the distant universe. As it travels through space, the signal from an FRB gets stretched, or 'smeared,' in time. The more 'missing' matter it passes through, the more smeared the signal becomes. The MIT-led team measured the degree of smearing experienced by thousands of FRB signals detected on Earth. Then, they compared each FRB smear with galaxy locations across the universe to determine how much of an FRB's smearing was due to galaxy matter versus other 'missing' matter. The new method revealed not only whether 'missing' matter was present but also where. Specifically, the researchers discovered that it exists in very diffuse clouds surrounding groups of galaxies. These clouds extend out from the galaxies, to much further distances than scientists had predicted. Blogger's Review: This discovery provides new insights into the distribution of matter in the universe, indicating that there is a significant amount of 'missing' matter in the space between galaxies. This matter may have been ejected from galaxies through high-energy processes, which has important implications for our understanding of the universe's evolution.