When did the universe 'wake up'?

It was a big moment for our cosmos when the first stars awoke, but it's an elusive one for scientists.

In new research, however, a team of astronomers has identified some of the oldest galaxies ever seen. These objects were already fully formed when the universe was just 680 million years old, according to the scientists, who also found evidence that these galaxies were flooding their surroundings with extreme ultraviolet radiation.

That flood formed gigantic bubbles, where the neutral gas became energized and ionized, offering astronomers the first direct image of a major transformational epoch in our universe.

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(Image: NASA, ESA and V. Tilvi (ASU)

By transforming light-quenching hydrogen atoms into ionized gas, ultraviolet starlight may have formed overlapping, giant bubbles filled with ionized hydrogen throughout the early universe.

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This visualization shows how ultraviolet light from the first stars and galaxies gradually transformed the universe. Hydrogen atoms, also called neutral hydrogen, readily scatters UV light, preventing it from traveling very far from its sources.

Gradually, intense UV light from stars and galaxies split apart the hydrogen atoms, creating expanding bubbles of ionized gas. As these bubbles grew and overlapped, the cosmic fog lifted. Astronomers call this process reionization.

Here, regions already ionized are blue and translucent, areas undergoing ionization are red and white, and regions of neutral gas are dark and opaque.