NGC 7635, commonly known as the Bubble Nebula, is an emission nebula located in the constellation Cassiopeia at a distance of approximately 7,100 light-years. The nebula is part of a larger HII region and is energized by a massive, hot O-type star (BD+60°2522) near its center. This star drives a powerful stellar wind that expands outward, sweeping up the surrounding interstellar gas and dust to form the nearly spherical “bubble” structure seen in the image.
The bubble itself is not perfectly symmetric due to variations in the density of the surrounding interstellar medium. As the stellar wind encounters denser regions, the expansion slows, creating a distorted shell and enhancing the bright rim where shock fronts compress and heat the gas. The glowing shell is primarily hydrogen emission, while oxygen and sulfur contribute to the subtle color variations that reveal the physical conditions within the nebula.
Surrounding the bubble is a complex field of ionized gas and dark dust structures, part of the larger nebular environment in which the star formed. These regions show evidence of ongoing interaction between radiation, stellar winds, and the interstellar medium, illustrating the dynamic processes that shape star-forming regions over time.
This image was created using a combination of narrowband (SII, H-alpha, OIII) and broadband RGB data acquired from Arnold, CA. The data were collected between September 13, 2021 and October 9, 2021, with a total integration time of 21.5 hours. The processing emphasizes the shock front and ionization structure of the bubble through SHO mapping, while RGB data preserves natural star color and enhances the surrounding star field.