Green Pea galaxies may resemble galaxies that reionized the early universe

Ars Technica : Green Pea galaxies , first recognized in 2007 as part of the Galaxy Zoo project, were given their name because of their small size and greenish color. Of the more than 1 million galaxies identified in data from the Sloan Digital Sky Survey , only 251 have been identified as Green Peas. Investigation of the galaxies revealed that their color comes from unusually high levels of oxygen emission, specifically doubly ionized oxygen ; notable quantities of ionized hydrogen and helium were also found. Although the spectral lines usually result from UV radiation caused by supermassive black holes, other signs of the presence of black holes are absent. The UV radiation therefore mostly likely comes from massive stars and the star formation process. Most galaxies have large enough concentrations of free gases to absorb the radiation before it exits the galaxy. But Green Pea galaxies have comparatively very low levels of gases. Anne Jaskot and Sally Oey of the University of MichiganâAnn Arbor believe that the combination of characteristics could have been shared by the galaxies responsible for reionization âmdash;the stripping of electrons from atoms that made the universe transparent 380â000 years after the Big Bang.