In particular, the cluster contains type O stars---rare, very hot stars that burn hotter and bluer than others. These O-type stars burn hot enough that they emit the UV radiation necessary to ionize the hydrogen, which results in the glow that is captured here. There are several clues as to which star is causing most of the glow. First, the brighter nebula is roughly round-ish, and the round shape has a radius. Second, the nebula contains several "elephant trunks"---dust pillars that are being slowly washed away by the ultraviolet light; at the edges of each pillar is an ionization front where we are looking across a plane of ionized gas. All the dust pillars share a common "radiant," a point where the UV appears to originate. Third, at that radiant sits an O-type star that is capable of causing the glow and the washing away. Spectral studies suggest that this one star is the hottest star within 3,000 light years of us. It is called BD +66 1673. I've pointed it out in a close-up below. This may well be the star that powers the nebula. Another study reports nine O7- to B3-type stars in the cluster. Surely they help some, too. Oh, why aren't the hot O and B stars blue? Too much dust in the way reddens their color along our line of sight. Here is the connection between BD +66 1673 and the dust pillars.
The nebula contains some fascinating areas. I've highlighted some below.
Finally, the view is full of dust clouds that lie in front of everything and block the view of what is behind.
This wonderful data came from DSW's FSQ and represents 31;21;21;16 x 900" of LRGB,over 22 hours of data.
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