More than three-quarters of the baryonic content of the Universe resides in a highly diffuse state that is difficult to detect, with only a small fraction directly observed in galaxies and galaxy clusters^1,2. Censuses of the nearby Universe have used absorption line spectroscopy^3,4 to observe the ‘invisible’ baryons, but these measurements rely on large and uncertain corrections and are insensitive to most of the Universe’s volume and probably most of its mass. In particular, quasar spectroscopy is sensitive either to the very small amounts of hydrogen that exist in the atomic state, or to highly ionized and enriched gas^4,5,6 in denser regions near galaxies⁷. Other techniques to observe these invisible baryons also have limitations; Sunyaev–Zel’dovich analyses^8,9 can provide evidence from gas within filamentary structures, and studies of X-ray emission are most sensitive to gas near galaxy clusters^9,10. Here we report a measurement of the baryon content of the Universe using the dispersion of a sample of localized fast radio bursts; this technique determines the electron column density along each line of sight and accounts for every ionized baryon^11,12,13. We augment the sample of reported arcsecond-localized^{14,15,16,17,18} fast radio bursts with four new localizations in host galaxies that have measured redshifts of 0.291, 0.118, 0.378 and 0.522. This completes a sample sufficiently large to account for dispersion variations along the lines of sight and in the host-galaxy environments¹¹, and we derive a cosmic baryon density of \({\varOmega }_{{\rm{b}}}={0.051}_{-0.025}^{+0.021}{h}_{70}^{-1}\) (95 per cent confidence; h₇₀ = H₀/(70 km s⁻¹ Mpc⁻¹) and H₀ is Hubble’s constant). This independent measurement is consistent with values derived from the cosmic microwave background and from Big Bang nucleosynthesis^19,20.

Published recently in Nature, an international team of researchers has observed a massive, rotating disk galaxy just 1.5 billion years after the Big Bang —1.5 billion years earlier in cosmic history than astronomers had expected to find such a galaxy based on previous studies. The research has fueled debate about how galaxies in the early Universe assembled.

The observations were made using one of the most powerful radio telescopes in the world, the Atacama Large Millimeter/submillimeter Array (ALMA), in the Atacama Desert in northern Chile.

“This is an exciting discovery for astronomers because it provides clues as to how large-scale structure began to form in the Universe,” said Dr. Alfred Tiley from the UWA node of the International Centre for Radio Astronomy Research (ICRAR).

Half of the normal matter in the universe has been hiding since the Big Bang. Astronomers have just detected it for the first time.

In the late 1990s, cosmologists made a prediction about how much ordinary matter there should be in the universe. About 5%, they estimated, should be regular stuff with the rest a mixture of dark matter and dark energy. But when cosmologists counted up everything they could see or measure at the time, they came up short. By a lot.