The Bubble Nebula is 7,100 light-years from Earth in the constellation Cassiopeia and is 7 light-years across. It was discovered in 1787 by William Herschel.
The bubble is being formed by an extremely bright, massive (about 45 times more massive than our Sun) and short-lived star O star (BD +60°2522) that has lost most of its outer hydrogen and is now fusing helium into heavier elements. The star is about 4 million years old and in 10 million to 20 million years, it will likely detonate as a supernova.
Gas on the star gets so hot that it escapes away into space as a "stellar wind" moving at over 4 million miles per hour. This outflow sweeps up the cold, interstellar gas in front of it, forming the outer edge of the bubble. As the surface of the bubble's shell expands outward, it slams into dense regions of cold gas on one side of the bubble. This asymmetry makes the star appear dramatically off-center from the bubble, at about 9 o'clock in the image.
Dense pillars of cool hydrogen gas laced with dust can be seen in places around the bubble, most clearly to its left in the image [1].
The image was taken over three short nights in December and initially I processed the nebula as HSO but the combination obscured both the massive star and the pillars of hydrogen and so it was reprocessed as SHO.
[1]
https://hubblesite.org/contents/media/images/2016/13/3725-Image.html
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