Between 11.7 to 11.3 billion years ago, ultraviolet (UV) light emitted by quasars—enormous galaxies with supermassive black holes at their centers—stripped electrons of cosmic helium, according to observations made with the Cosmic Origins Spectrograph (COS) on NASA's Hubble Space Telescope. The big bang that created our universe occurred around 13.7 billion years ago.

The electron-stripping process, known as ionization, heated the helium gas from 18,000 to nearly 40,000 degrees Fahrenheit (10,000 to 22,000 degrees Celsius).

(Related: "Immaculate Black Holes Found Near Universe's Conception.")

Warm gas moves faster than cool gas, and the heated helium sped free of the gravitational clutches of so-called dwarf galaxies. Helium, the second most abundant