Half the matter in the universe was missing. We found it hiding between galaxies.
It took the discovery of a new celestial phenomenon and entirely new telescope technology.
Diligence, technological progress, and a little luck have together solved a 20-year mystery in the cosmos.
J. Xavier Prochaska is a professor of Astronomy & Astrophysics at the University of California, Santa Cruz. Jean-Pierre Macquart is an associate professor of Astrophysics at Curtin University. This story originally featured on The Conversation.
In the late 1990s, cosmologists made a prediction about how much ordinary matter there should be in the universe. About 5 percent, 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.