Astronomers and cosmologists have an inventory problem: They haven’t been able to account for a fair amount of the stuff that makes up our universe.
There are the longstanding challenges with pinpointing dark energy and dark matter, two invisible components that together make up more than 95 percent of the cosmos. But there is also the lesser-known problem of missing baryon particles.
Baryons are subatomic particles that include protons and neutrons, which form the nuclei of atoms. Baryonic matter — part of what we consider “normal matter” in the universe — makes up everything we are familiar with: stars, planets, the chair you are sitting on, the device you are using to read this, and you.