NGC-7635, The Bubble Nebula

NGC 7635 (The Bubble Nebula) is an iconic emission nebula shaped by the intense stellar winds of a massive, hot star. It was discovered on November 3, 1787, by William Herschel, who initially described it as a "faint nebulosity" surrounding a 9th-magnitude star. The central star SAO 20575 is a massive O-type star roughly 45 times more massive than our Sun. The "bubble" is created as the star’s stellar winds—traveling at over 4 million miles per hour—plow into the surrounding cold, molecular gas, pushing it into a shell that expands at a rate of roughly 4 light-years per million years. Interestingly, the bubble is asymmetrical; because the shell encounters denser gas on one side than the other, the star appears dramatically off-center rather than in the middle.