"What are yellow balls?"

Citizen scientists asked astronomers that question and led them to a celestial mystery, according to a press release by NASA's Jet Propulsion Laboratory (JPL) and the Iowa State University in Ames.

The mystery objects weren't actually yellow, but they looked that way through NASA's infrared Spitzer Space Telescope. They look small, but are several hundred to thousands of times bigger than our solar system, according to the press release.

"The volunteers started chatting about the yellow balls they kept seeing in the images of our galaxy, and this brought the features to our attention," said co-author Grace Wolf-Chase of the Adler Planetarium in Chicago.

"With prompting by the volunteers, we analyzed the yellow balls and figured out that they are a new way to detect the early stages of massive star formation," saidlead author Charles Kerton of Iowa State University, Ames. "The simple question of 'Hmm, what's that?' led us to this discovery."

"Bubbles" are seen in space as stars explode and create new stars. Yellow, it has been determined, is the first color in the formation of a new star, preceeding the "green pea" stage discovered by astronomy volunteers.

"The yellow balls are a missing link," said Wolf-Chase, "between the very young embryonic stars buried in dark filaments and newborn stars blowing the bubbles."

"If you wind the clock backwards from the bubbles, you get the yellow ball features," said Kerton.

The findings have been published in Astrophysical Journal.