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Tim Kendall's Extreme Astrophysics

Light from Universe’s first galaxies observed

16 Oct 2015, 09:30 UTC
Light from Universe’s first galaxies observed
(200 words excerpt, click title or image to see full post)

The three panels show the different components of extragalactic background light detected with the Hubble Space Telescope. Image Credit: Ketron Mitchell-Wynne, UC Irvine. Text: Scientific American.

In between the thousands of bright galaxies that populate many Hubble Space Telescope photos of the distant cosmos are empty dark spots—tantalizing patches that could be chock-full of more galaxies if only we could see them. Now, astronomers have taken another look at those empty patches and spotted faint light streaming from stars formed only 500 million years after the Big Bang. The new results (pdf) suggest this light came from some of the first galaxies ever formed, which could be 10 times more numerous than previously thought.
This so-called “extragalactic background light” likely dates from roughly 250 million years after the Big Bang. Shortly after the birth of the universe, space was filled with a hot, dense fog of ionized gas. But over hundreds of thousands of years, the gas expanded and cooled, allowing giant clouds of hydrogen and helium to collapse and form the first stars. Ever since these stars first ignited, their light—and all the light from successive generations of stars—has been filling the universe, creating a pervasive glow throughout the ...

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