[1] Scientists believe bubbles in these images are the result of young, massive stars whose light causes shocks in interstellar gas.
[6] The annulus tool that was used to mark the bubbles in the Milky Way Project phase 1 was at random round and needed improvement.
They are now called yellow balls, a mix of compact star-forming regions that show transition into bubbles.
For this goal the 24 μm part of the image is important: Bubbles are more easy to spot and bowshocks are most of the time visible at this wavelength.
The MWP classification aggregation pipeline is continuously tested and modified to avoid issues that were encountered in DR1.
The size of the bubbles in the catalog is proven to be as good as expert classifications and to be better than in previous works.