What is known about HDW3 or Hartl-Dengel-Weinberger 3 is very little. A planetary nebula ~11 l.y. in diameter, located in the constellation Perseus at ~3000 l.y. away from Earth. The white dwarf is a 17m small point (closest one down from the large orange star in the arc). The star that has exploded has been moving upward and the dwarf continues to move, however the surrounding interstellar gas slows the nebula down. This leads to several effects. The moving bubble forms shock fronts - denser structures in the direction of movement. The white dwarf that doesn't slowdown, will one day be completely outside the nebula it created. It also heats these fronts with its ultraviolet light more than the areas on the opposite side, creating this unusual view.
Seeing two arches makes me wonder if it could possibly be a sign of two explosions?
HDW3 is insanely faint. Stretching individual subs can't confirm if the subject is there and well framed... I had to collect about half an hour to be sure I wanted to continue shooting without changing the position. The whole project took 7 nights and more than 40 hours to get a satisfying result and is bettering my previous personal record of 38h spent on the Bubble nebula
EDIT: In Facebook Pierre Vandevenne gave a link that can explain very well the image
Reverse shock wave can explain the two arches and the "tiara" structure...
https://academic.oup.com/mnras/article/435/1/320/1110827https://www.astrophotography.app/
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