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Millions of Years After Big Bang, a 'Cosmic Dawn'

Astronomers say they've figured out when first stars began shining
By Jenn Gidman,  Newser Staff
Posted Jun 25, 2021 12:43 PM CDT

(Newser) – For his entire working life, Richard Ellis has been obsessed with finding out when the universe's first stars began shining. Now, in a new study published in the Monthly Notices of the Royal Astronomical Society journal, Ellis and his team at University College London say they've pinpointed the start of this "cosmic dawn," noting we may even be able to, in the very near future, watch these first galaxies being born, thanks to a new high-powered telescope. Per the Guardian, the universe came into existence after the Big Bang 13.8 billion years ago, an event that was followed by a few hundred million years of starless darkness. To determine how long ago it was when stars did form, Ellis and his colleagues first used the Hubble and Spitzer space telescopes to examine starlight from six of the most distant galaxies—whose light has taken nearly the universe's entire life to reach us—calculating the stars' ages by looking at the proportion of hydrogen atoms in the stars' atmosphere.

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Then, using four of Earth's largest ground-based telescopes, the scientists spent 70 hours observing the galaxies to figure out how far away they actually were. Knowing all of these factors, the researchers then determined that the stars in these galaxies started shining between 250 million to 350 million years after the Big Bang. Ellis tells the Guardian that, because the ages of the six galaxies they examined were all a bit different, it signals there was a gradual "switching on" of the stars, rather than one massive, sudden powering up. NASA's James Webb Space Telescope, set to launch in the late fall, may even be powerful enough to pick up the birthing of these stars, with images possible as soon as early next year. "The holy grail has been to look back far enough that you would be able to see the very first generation of stars and galaxies," Ellis tells the BBC. "Now we have the first convincing evidence of when the universe was first bathed in starlight." (Read more stars stories.)

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