NGC 7635

The Bubble Nebula (NGC 7635) is an emission nebula located about 7,100 light-years away in the constellation Cassiopeia, sculpted by the intense stellar wind of a massive O-type star (BD+60°2522) embedded within a dense molecular cloud. That fast wind sweeps into the surrounding gas, compressing it into a thin, glowing shell roughly ten light-years across. Because the bubble is expanding into an uneven environment rather than empty space, its rim is brighter on one side and the structure appears slightly distorted rather than perfectly spherical.

This image was captured using narrowband imaging in H-alpha, [O III], and [S II], isolating emission from different physical regions of the nebula. Hydrogen-alpha traces the broader field of ionized gas and the bright arc of the shell, oxygen highlights the hotter, more energetic interior, and sulfur emphasizes denser, shock-excited regions where the stellar wind collides with surrounding material. Together, these narrowband signals reveal the Bubble Nebula as an active boundary between a powerful star and the interstellar medium that contains it.