What About the Blue Star?
The core of the nebula is an 8.7 magnitude blue star known as SAO 20575 or BD+60 2522. It is almost 40 times more massive than our Sun, emitting a wind so hot and intense that it pushes any surrounding sparse gas into a shell. The energetic radiation emitted from the star ionizes this shell, causing it to glow.
More specifically, the star—depicted at the lower center of this image—is so energetic that it is constantly shedding material into space at an incredibly fast pace. This material is being shaped into a bubble due to the resistance of the hot and dense gas that surrounds the stellar core. Its irregular shape is a result of encounters with gases of different thickness in different directions. The yellow clouds to the right of the star consist of much denser gas. The lower portion of these clouds appears brighter because it is closer to the stellar core and therefore heated and eroded at a much faster pace. More detailed analysis has shown the existence of loops and arcs between the yellow cloud region and the star. These are probably the result of material collision due to the star's intense wind as well.
Scientists claim that this is actually a rare case of a star located within the gas cloud, whose outward wind forms such an expanding bubble-shaped formation.
General characteristics of the central star SAO 20575:
Declination: +61o 11' 40.6''
Distance: ~ 3.6 kpc
Spectral type: O6.5
Apparent magnitude: 8.7
Absolute magnitude: 9.0
Terminal wind velocity: ~ 1800 km/s
Rate of stellar mass loss (M⊙yr−1): 10 -5.67