NGC 7635 (Bubble Nebula)

Constellation: Cassiopeia

Distance: 7100 light years

NGC 7635, also called the Bubble Nebula, is a H II region emission nebula discovered in 1787 by William Herschel. The "bubble", measuring 10 light years across, is created by the stellar wind from a massive hot, 8.7 magnitude young central star (SAO 20575 or BD+602522), thought to have a mass of 40 times that of our sun and several hundred times more luminous (in this photo, this star is in the upper right portion of the "bubble"). This unusually powerful star is known as a Wolf-Rayet star, named after the French astronomers Charles Wolf and Georges Rayet who first described the unusual stars in 1867. The shape of the Bubble nebula marks the leading edge of the Wolf-Rayet wind front as it plows into the denser stationary material of the interstellar medium.