In the early universe, the gas between stars and galaxies was opaque – energetic starlight could not penetrate it. But 1 billion years after the big bang, the gas had become completely transparent. Why? New data from NASA’s James Webb Space Telescope has pinpointed the reason.

In the early universe, the gas between stars and galaxies was opaque – energetic starlight could not penetrate it. But 1 billion years after the big bang, the gas had become completely transparent. Why? New data from NASA’s James Webb Space Telescope has pinpointed the reason.