Mysterious 'Yellowballs' Spotted by Citizen Scientists are Baby Massive Stars

About four years ago, a citizen scientist that was looking for the tell-tale bubble patterns of star formation in the Milky Way Project found something else: bright yellow, fuzzy objects. Now, scientists have discovered exactly what these "yellowballs" actually are.

The Milky Way Project is part of the Zooniverse, a collection of Internet-based science projects that ask for the public's help looking through images and other data. The Milky Way Project itself asks people to study tens of thousands of Spitzer's infrared images. People are asked to circle and classify various objects, including bubbles of gas and dust blown by the radiation and charnged particles from bright young stars.

Yet this project took a detour when citizen scientists noticed "yellowballs" along the rims of some bubble formations. Astronomers began studying these yellowballs by cross-matching them against existing catalogs of space objects. They also studied the luminosity and physical sizes of 138 of the yellowballs.

In the end, the researchers found that most of the yellowballs were located in regions of the galaxy containing dense gas. They also found that yellowball luminosity was consistent with the luminosity expected for a collection of newly formed massive stars. It's likely that there's an early "yellowball stage" in the formation of stars 10 to 40 times as massive as our sun.

"All massive stars probably go through this yellowball stage," said Charles Kerton, one of the researchers, in a news release. "The most massive stars go through this stage very early and quickly. Less massive stars go through this stage more slowly."

The findings reveal exactly what this yellowball stage is. That said, further studies of yellowballs will improve astronomers' understanding of how regions of massive star formation grow from early compact stages to more evolved and bubble-like structures.

The findings are published in The Astrophysical Journal.

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