The "bubble" (NGC 7635) is created by the stellar wind from a massive hot, 8.7[1] magnitude young central star.
The radiation of the star is strong enough to excite the surrounding hydrogen gas to glow.
Its distance is about 8800 light years from us.
M52 - an young open star cluster is visible in the upper left corner. It has a distance of about 4600 light years from us.