First there were "green pea" galaxies.
Those are members of a rare class of very small, bright green galaxies that produce stars prolifically.
Green peas were discovered through an online project called Galaxy Zoo, in which more than 200,000 volunteers classified objects in an image bank. Only 250 green peas turned up among 1 million images scanned, according to a 2009 Yale University-led study published by the Royal Astronomical Society of England.
Now, thanks to observations from Mauna Kea, "green bean" galaxies have appeared on the cosmic menu.
German astronomer Mischa Schirmer, a science fellow at the Gemini South Observatory in Chile, was conducting a study of galactic superclusters when he stumbled across the first regular-size green galaxy in December 2010. The image was from the Canada-France-Hawaii Telescope.
The galaxy, named J2240-0927, lies in the constellation Aquarius 3.7 billion light-years from Earth.
"Certainly there are odd galaxies out there," Schirmer said by email Sunday. "When I saw J2240-0927 the first time I was literally at a loss for words. It was unlike any other galaxy I have ever seen, simply bizarre, and absolutely unexpected. It just shouldn’t be there, yet it has been evident that it is not an artifact from data processing, but very, very real."
He quickly booked observing time with the European Southern Observatory’s Very Large Telescope array in Cerro Paranal, Chile, high in the Atacama Desert.
"Ten minutes after the data were taken in Chile, I had them on my computer in Germany," Schirmer recalled. "I soon refocused my research activities entirely as it became apparent that I had come across something really new."
Many galaxies, including the Milky Way, have a giant black hole at their center that causes the gas around it to glow. With green bean galaxies the entire galaxy is glowing in the color of ionized oxygen: green.
Since the initial discovery, Schirmer’s team searched through a list of nearly a billion other galaxies in a database called the Sloan Digital Sky Survey.
They found 16 more.
Their color is the only similarity to green peas.
Schirmer and his team say the black holes were once very active but now appear to be dying down. They suggest the glowing regions could be an "echo" from when the central black hole was much more active, and will dim as the remnants of radiation pass out into intergalactic space.
A paper detailing the findings will be published in the Astrophysical Journal.
