Bubbles produced by young massive stars vs. Planetary Nebulae around old stars
by gwolfchase scientist
The large bubbles in MWP images that have distinctive 'red' interiors and 'green' rims are mostly formed by stellar winds and ionizing radiation from very young massive stars; on the other hand, planetary nebulae will typically appear as small red circles. That said, the fact that we don't know the distances to many of these objects complicates things considerably (for example, very distant bubbles around massive young stars will appear smaller.) Several members of the MWP team are currently working to develop methods to distinguish different types of objects by their infrared 'colors', and other factors, such as their association with dense clouds forming new stars. The catalog that was the result of volunteer classifications has been enormously useful in expanding the number of known bubbles so we have a larger database with which to work!