By Ron Cowen
For galaxies, it’s not easy being green. Most of them appear blue or red from Earth.
Indeed, after combing through an online image bank of 1 million galaxies, volunteers for the Galaxy Zoo project have found a mere 250 galaxies with an unusual, greenish color. These compact bodies, dubbed the Green Peas, are only about one-tenth the size of the Milky Way.
Now, a team of astronomers working with the volunteers has discovered that the Green Peas are hamming it up, forming stars at an enormous rate — about 10 times faster than the Milky Way. Spectra of the galaxies taken by the Sloan Digital Sky Survey — the source of the online images — indicate that the greenish hue comes from the glow of ionized oxygen gas heated by newborn stars, says astronomer Carolin Cardamone of Yale University.
High rates of star formation are common among some remote galaxies, which hail from the early universe, but the Green Peas are relatively nearby — between 1.5 billion and 5 billion light-years from Earth. The Green Peas may represent a closer, and therefore easier to observe, analog of those distant galaxies, report Cardamone and her colleagues in an upcoming Monthly Notices of the Royal Astronomical Society. The team has also posted the findings online at arxiv.org.