Hubble Solves Mystery Of Strange Green Cloud

Voorwerp discoverer Hanny Van Arkel of Holland. Credit: Edd Edmonson

Back in 2007, the Sloan Digital Sky Survey, a deep mapping survey of galaxies using a 98-inch telescope based in New Mexico, photographed a strange blue-green cloud next to the galaxy IC 2497 located in the constellation of Leo Minor. It was later flagged by Hanny Van Arkel, a Dutch schoolteacher participating in the online Galaxy Zoo project. You’ll recall the Galaxy Zoo invites the public to examine and classify photos of galaxies taken by Sloan Survey and Hubble Space Telescope. Hanny noticed the strange cloud and alerted the project coordinators to it. It was soon nicknamed Hanny’s ‘Voorwerp’ (Dutch for ‘object’) and astronomers scheduled additional observations of the odd bit of fluff with the Swift satellite, the Hubble and others.

The spiral galaxy IC 2497, 650 million light years from Earth, and neighboring green cloud. Light from beams of radiation given off as material falls down a black hole at the galaxy's center lights up the cloud. Click to enlarge. Credit: NASA/ESA/William Keel and the Galaxy Zoo team

Based on new photos and observations shared today by astronomer Bill Keel of the University of Alabama in Tuscaloosa and leader of the Hubble study, astronomers say the weird cloud is a long streamer of gas pulled out of IC 2497 by the gravity of a passing galaxy. The interaction between the two galaxies dumped gas into a black hole in IC 2497’s core which lit up like a proverbial Christmas tree. As the gas swirled down the hole, friction heated it to millions of degrees, creating beams of radiation that lit up the cloud like a helicopter spotlight on a nighttime crime scene.

Outflows of gas – perhaps from the black hole – were also found streaming from the galaxy’s center toward the cloud. Where they collided, the gas compressed the green cloud’s gas, causing parts of it to collapse into dense lumps that quickly evolved into fresh stars. Hubble detected delicate filaments of gas and a pocket of young star clusters in the giant object, which is the size of the Milky Way.

This step by step illustration explains how a passing galaxy set off a chain of events that led to the green cloud. A quasar or "quasi stellar object" is an active, supermassive black hole at the center of a distant galaxy. Click to enlarge. Credit: NASA/ESA

It’s incredible to think that two galaxies passing in the night would lead to the creation of a new galaxy rocked with waves of fresh star formation. Even better – the discovery was made by a schoolteacher with a keen sense of curiosity, a qualification known to open doors to many places. If you’ve ever wondered whether you can really contribute anything new to science, the answer is ABSOLUTELY! There are more ways to do so now than ever.

Young star clusters are buried in the yellow orange knots within the cloud. The green color comes from glowing oxygen. Credit: NASA/ESA

Every time we turn around, the universe puts on a fresh, often surprising face. For more on the news, check out this press release. You’ll also want to stop by Hanny’s blog to learn more about the discovery and her impressions of the U.S. She’s in Seattle at the American Astronomical Society meeting where the news was announced today.

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