Bubble Nebula (NGC 7635)

The bubble is generated by BD+60°2522, a massive O-type star whose intense stellar winds and ultraviolet radiation push outward into the surrounding interstellar gas. The star is estimated to be roughly 10 to 20 times the mass of the Sun and emits a stellar wind that compresses the gas into the visible shell.

The bubble structure spans approximately 7 to 10 light-years in diameter, vastly larger than the distance between the Sun and the nearest star. The nebula sits roughly 7,100 to 11,000 light-years from Earth, with distance estimates varying due to uncertainty in measuring objects in the direction of Cassiopeia.

NGC 7635 is located in the constellation Cassiopeia, a circumpolar constellation visible year-round from most of the northern hemisphere. It was discovered by William Herschel in 1787 during his systematic sky surveys.

NGC 7635 is a faint visual target that typically requires at least an 8-inch aperture telescope and dark-sky conditions to discern its bubble structure. Astrophotographers frequently image it, however, because narrowband filters reveal striking detail in the surrounding hydrogen and oxygen emission gas.