Citizen scientists help solve ‘yellow balls’ puzzle

Strange objects in Spitzer images identified with help from the Milky Way Project

In this Spitzer image you can see red dust clouds, green bubbles… and 'yellowballs' 

Credit: NASA/JPL-Caltech

By Russell Deeks

Participants in the online citizen science initiative The Milky Way Project have helped to identify a new class of object in space. The Milky Way Project (MWP) is one of several citizen science projects run through the Zooniverse website - Galaxy Zoo is another - and users had been asked to help categorise objects seen in images of the plane of the Milky Way taken by the Spitzer Space Telescope.

The Spitzer images are colourised according to the infrared wavelengths detected, with infrared light of 3.6 microns shown in blue, 8-micron light shown in green and 24-micron light shown in red. The pictures clearly show many red areas (dust clouds) and many green bubbles, which indicate that a newly formed star is clearing its neighbourhood by blowing away dust with wind and radiation.

What the citizen scientists noticed, though, was that the images also showed a large number of 'yellowballs' - roughly spherical objects that appear yellow under Spitzer's colourisation system. Although they look quite small in the pictures, each yellowball is several hundred or even several thousand times the size of our Solar System. 

With over 900 yellowballs identified by MWP users, the Spitzer scientists decided to investigate the previously unidentified phenomenon. They have since concluded - in a paper published in the Astrophysical Journal - that the yellowballs represent an earlier stage of star formation. "The yellow balls are a missing link between the very young embryonic stars buried in dark filaments and newborn stars blowing the bubbles," said Grace Wolf-Chase from Chicago's Adler Planetarium, who is co-author of the report.

Her fellow co-author, Charles Kerton of Iowa State University, Ames, said: "If you wind the clock backwards from the bubbles, you get the yellow ball features."

Wolf-Chase added that the new findings "attest to the importance of citizen scientist programmes".


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