Amateurs discover green pea galaxies

An army of space fans have surprised professional astronomers by discovering a scattering of previously unrecognised galaxies that look like green peas.

Experts are hailing the find as of great importance because it will help them to learn how stars were born in the early universe.

Two rows of peas from the 250 discovered by Galaxy Zoo fans

Hundreds of thousands of volunteers – ordinary members of the public – signed up for the UK-led project called Galaxy Zoo, which began operating in July, 2007.

They have been using their spare time on their home computers to click through pictures of more than a million galaxies taken by a robotic camera for the Sloan Digital Sky Survey in New Mexico to help classify them.

While checking through the online image bank, the space fans came across 250 galaxies that stood out because they were small but bright green. They quickly dubbed them the Green Peas and the discoverers jokingly call themselves the Peas Corps.

Professional astronomers checked them out and found that the “peas” the volunteers had harvested were rare, small and compact galaxies where stars were being born at an extremely high rate.

Now their amazing discovery is being reported in a major scientific paper to be published in leading journal the Monthly Notices of the Royal Astronomical Society.

Oxford astronomer and presenter of the BBC’s The Sky At Night Chris Lintott, who set up Galaxy Zoo and is its Principal Investigator, said: “This is a fantastic result for the project. These peas had been hidden in the data for decades. Only when our volunteers spotted them and wondered what they were did the professionals investigate.

“They look insignificant as little green blobs but they turn out to be some of the most important galaxies we’ve found. And it all stems from the fans asking about them in their online chat room.”

Last year the Zooites, as the fans call themselves, discovered another new type of galaxy called red spirals.

Chief author of the latest paper, Carolin Cardamone, a professional astronomer at Yale University, said: “These are among the most extremely active star-forming galaxies we’ve ever found.

“No one person could have done this on their own. Even if we had managed to look through 10,000 of these images, we would have only come across a few Green Peas and wouldn’t have recognized them as a unique class of galaxies.”

The galaxies lie between 1.5 billion and 5 billion light years away from Earth and are ten times smaller than our own Milky Way galaxy and 100 times less heavy. But despite their small size, they are forming stars ten times faster than the Milky Way.

Kevin Schawinski, also at Yale, who helped found the Galaxy Zoo project said: “They’re growing at an incredible rate. These galaxies would have been normal in the early universe, but we just don’t see such active galaxies today. Understanding the Green Peas may tell us something about how stars were formed in the early universe and how galaxies evolve.”

You can get involved in the Galaxy Zoo project by visiting their website here.

• Discover space for yourself and do fun science with a telescope. Here is Skymania’s advice on how to choose a telescope. We also have a guide to the different types of telescope available.


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By Paul Sutherland

Paul Sutherland has been a professional journalist for nearly 40 years. He writes regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy, plus he has authored three books on astronomy and contributed to others.

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