The first galaxies burned with green fire.

Science News didn’t get so poetic with their headline, but it amounts to the same thing. A team of astronomers has found a blaze of a specific wavelength of green light that shows the first galaxies were filled with hotter stars:

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.