This is NGC281, or the “Pac-Man” nebula. I think it’s one of those objects that might look a little like its name if you’re viewing it through a big telescope in a dark sky, but takes on a totally different character in long-exposure, narrowband images such as this.
This is a total of 13 hours of exposure in the “Hubble Palette” for the nebula itself (where colors represent specific ionized emissions from its gases), with the stars in their true colors. You’ll find it within the constellation Cassiopeia, about 9,500 light-years away in the Milky Way’s Perseus arm. Look closely, and you’ll see many dark “Bok Globules” within the nebula – these are especially dense areas of gas that block the light behind them, and may be areas of active star formation within.
To highlight the structure of the gases of the nebula itself, here’s a version with the surrounding stars removed: