Astronomers from the Centre for Astrophysics | Harvard & Smithsonian and Caltech have finally located the universe’s long-missing ordinary matter, known as baryonic matter, by using fast radio bursts (FRBs) as precise cosmic tools. These brief, powerful radio signals from distant galaxies allowed scientists to measure how much gas they passed through on their journey to Earth. The study found that about 76% of the universe’s baryonic matter is spread out in the intergalactic medium (IGM), the vast, thin gas between galaxies. The remaining matter resides in galaxy halos (15%) and inside galaxies themselves (9%).
This discovery solves the decades-old “missing baryon problem” and confirms predictions from cosmological simulations. It also reveals how feedback from black holes and supernovae pushes matter out of galaxies and into the IGM. The study marks a turning point in how we map the universe’s structure and is published in Nature Astronomy.