‘Yellowballs’ offer new insights into the formation of stars

A serendipitous discovery by citizen scientists has given a unique new window to the diverse environments that stars and star clusters produce, revealing the presence of ‘star nurseries’ before stars of babies appear from their birth clouds, according to the Planetary scientist Science Institute Grace Wolf Chase.

“Yellow balls are small compact features identified in infrared images obtained by the Spitzer Space Telescope during online discussions about the Milky Way project, an initiative on the online civic science platform zooniverse.org, which asked civic scientists to help identify features associated with , massive stars of more than ten solar masses, “says Wolf-Chase, lead author of ‘The Milky Way Project: Probing Star Formation with First Results on Yellowballs from DR2’, which was published in the Astrophysical Journal. “Early research suggested that yellow balls were produced by young stars while heating the surrounding gas and dust from which they were born.”

The yellow balls discovered by scientists shed infrared light at a very early stage in the evolution of star clusters, when they are a ‘mere’ hundred thousand years old. “This is the point at which their presence is first revealed, but they remain embedded in their dusty birth combs,” Wolf-Chase said. “It allows us to link the characteristics of stars to their birth environments, as if one were giving birth to a hundred babies at a time.”

The research shows that the formation of star clusters – protocol clusters – of virtually all masses goes through a yellow ball stage. Some of these protocol clusters form massive stars of more than ten solar masses that will form their environments in ‘bubbles’ through strong stellar winds and harsh ultraviolet radiation, while others do not. Over the course of a million years, bubbles can expand up to ten light years throughout.

“We have also shown that we can get information about the masses and ages of star clusters through the infrared ‘colors’ of yellow balls alone, without other extensive observations such as spectroscopy,” Wolf-Chase said. “This is important because the observation of time is limited and if we can tell a lot about thousands of these objects from a few, relatively simple observations, it is an excellent time saver and helps us to identify particularly interesting yellow balls for future observations with a higher resolution. ”

In the course of the search for ‘bubbles’ in the Milky Way project, citizen scientists used the discussion board of the project to mark small, round objects that looked “yellow” in the representative infrared images. “Scientists initially thought it could be very young versions of the bubbles, and we included identifying yellow balls as the main target in a version of the Milky Way project launched in 2016,” Wolf-Chase said. “This has led to the identification of 6,176 yellow spheres across more than one-third of the Milky Way. Their distinctive ‘yellow’ appearance is related to wavelengths that detect complex organic molecules and dust, as it is warmed by many young stars in their birth clouds. is embedded. ”

“Our article analyzes a subset of 516 yellow spheres and shows that only about 20% of yellow spheres form the bubbles associated with massive stars, while about 80% of these objects determine the location of regions that form less massive stars,” Wolf- Chase said. “This work demonstrates the great value of civic science in opening a new window to our understanding of star formation.”