NGC 7635 - Bubble Nebula

Bubble Nebula

The Bubble Nebula, also known as NGC 7635, Caldwell 11, or Sharpless 162, is an emission nebula located approximately 7,100 to 11,000 light-years away in the constellation Cassiopeia.  It appears as a vast, glowing cosmic bubble formed by the intense stellar wind of a massive, hot central star, BD+60°2522 (also cataloged as SAO 20575), which is about 45 times more massive than the Sun and emits a million times more light. 

The stellar wind, moving at over 4 million miles per hour, sweeps up surrounding interstellar gas and dust, creating the bubble's expanding shell.  The nebula spans about 7 to 10 light-years across and has an apparent magnitude of 10, making it observable with medium to large telescopes under dark skies.  Its asymmetric shape results from the uneven density of the surrounding interstellar medium, causing the central star to appear off-center. 

Discovered by William Herschel in 1787, the Bubble Nebula gained iconic status when NASA's Hubble Space Telescope captured a high-resolution image in 2016 to celebrate its 26th anniversary in space.