by gwolfchase scientist
Bubbles can be incomplete for several reasons. Sometimes, the entire bubble isn't seen in the field of view displayed in an image. Also, in many cases, as bubbles age and expand, they encounter more gas and dust in one direction than another -- in other words, they "break out" of the clouds in which the stars producing the bubbles were born. This looks like a good example! As noted, there are a number of 'knots' and small bubbles along the 'green' ridge, which makes this a good candidate for triggered star formation. Although it's difficult to prove cause and effect in these regions, identifying a large sample of candidates is a critical starting place!