NGC 7635 Bubble Nebula
NGC 7635, also called the Bubble Nebula, Sharpless 162, or Caldwell 11, is a H II region emission nebula in the constellation Cassiopeia.
The image is a LRGB stack of 15hrs (L 15x600" + 15x600" each RGB) calibrated, stacked and processed in Pixinsight
It is very close to the open cluster Messier 52 which is just outside the frame. The "bubble" is created by the stellar wind from a massive hot, 8.7 magnitude young central star, SAO 20575 (BD+60°2522). The nebula is near a giant molecular cloud which contains the expansion of the bubble nebula while itself being excited by the hot central star, causing it to glow. It was discovered in 1787 by William Herschel. The star BD+60°2522 is thought to have a mass of about 44 solar masses.