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: The galaxies’ stars emitted enough light to heat and ionize the gas around them, clearing our collective view over hundreds of millions of years.
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Source: Phys.org