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More Reionization

StarDate: 
November 4, 2016

A galaxy that’s 13 billion light-years away is helping us understand when the lights in the universe were switched back on. And that can help reveal when the first stars and galaxies were born.

A team of astronomers used one of the giant Keck telescopes in Hawaii to study some galaxies that appeared to be young, bright, and far away. Even with this large telescope, though, they were able to measure the distance to only one galaxy. It’s so far away that we see it when the universe was only about 700 million years old. That makes it one of the earliest galaxies in the universe.

Such galaxies formed as the gravity of clumps of dark matter pulled in gas. The gas then clumped together to make stars and galaxies.

Before these objects were born, the universe was dark. A few hundred thousand years after the Big Bang, the “soup” of energy and particles had cooled enough to form hydrogen atoms, which have no electric charge. The atoms emitted no radiation, and they had not yet come together to make stars, so there was nothing to emit light.

By the time the distant galaxy had formed, though, that was changing. Not only did the early galaxies shine brightly, but their light split the electrons from the hydrogen gas between galaxies — a process known as reionization.

It took a few hundred million years to complete that process. So the 13-billion-year-old galaxy was one of the earliest around — one of the first bright lights in the universe.

Script by Damond Benningfield

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