NGC 7635, also known as the Bubble Nebula, Sharpless 162, or Caldwell 11,is an H II region[1] emission nebula in the constellation Cassiopeia. It lies close to the direction of the open cluster Messier 52. The "bubble" is created by the stellar wind from a massive hot, 8.7[1] magnitude young central star, SAO 20575 (BD+60°2522).[7] 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.[7] It was discovered in 1787 by William Herschel.[5] The star BD+60°2522 is thought to have a mass of about 44 M☉.
