: Light emitted by a quasar when the universe was just 3 billion years old has revealed the presence of an enormous cloud of possibly primordial gas. When the light reached the gas, it excited the hydrogen atoms, causing them to emit UV radiation. As the universe expanded, that radiation stretched into the visible spectrum. Sebastiano Cantalupo and Xavier Prochaska of the University of California, Santa Cruz, and their colleagues found that visible light using the Keck Observatory. Their observations revealed that the cloud of gas stretched 1.5 million light-years, more than 10 times the diameter of the Milky Way. The team believes that the size of the cloud could mean that it stretches between multiple galaxies. If that turns out to be the case, it could be a remnant of the early structure of the universe. However, simulations suggest that the cloud has much more mass than would be expected.