Earliest galaxies got the green light | Science News



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Earliest galaxies got the green light

Emission of key color wavelength points to superhot first generation stars

5:26pm, January 9, 2017
NGC 6826

GREEN GALAXIES Galaxies in the early universe emitted lots of green light, such as seen in this nebula (NGC 6826) in the Milky Way.

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GRAPEVINE, TEXAS — Green was all the rage a couple of billion years after the Big Bang.

Galaxies in the early universe blasted out a specific wavelength of green light, researchers reported January 7 at a meeting of the American Astronomical Society. It takes stars much hotter than most stars found in the modern universe to make that light. The finding offers a clue to what the earliest generation of stars might have been like (SN: 10/1/16, p. 25).

Some nearby galaxies and nebulas produce a little bit of this hue today. But these early galaxies, seen as they were roughly 11 billion years ago, produce an overwhelming amount. “Everybody was doing it,” said Matthew Malkan, an astrophysicist at UCLA. “It seems like all galaxies started this way.”

Malkan and colleagues used the United Kingdom Infrared Telescope in Hawaii and the Spitzer Space Telescope to collect the light from over 5,000 galaxies. They found that, in all of these galaxies, one wavelength of green light — now stretched to infrared by the expansion of the universe — was twice as bright compared with light from the typical mix of stars and gas seen in galaxies today.

The green light comes from oxygen atoms that have lost two of their electrons. To knock off two electrons requires harsh ultraviolet radiation, possibly from lots of extremely hot stars — each roughly 50,000° Celsius. The sun, by comparison, is about a paltry 5,500° C at its surface.

“Stars must have been much hotter than most energetic stars familiar to us today,” said Malkan. How they got so hot — perhaps via exotic chemical abundances or just piling on lots of mass — is unsettled.


M.A. Malkan and D. Cohen. The universe going green: extraordinarily strong [OIII]5007 in typical dwarf galaxies at z~3. 229th meeting of the American Astronomical Society, January 7, 2017, Grapevine, Texas.

Further Reading

C. Crockett. Anna Frebel digs a young universe. Science News. Vol. 190, October 1, 2016, p. 25.

C. Crockett. Tiny galaxies had big influence on early universe. Science News Online, June 20, 2014.

R. Cowen. Seeing green: Color of the cosmos. Science News. Vol. 161, January 26, 2002, p. 62.

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