Two shells here, made by stars at opposite ends of the mass scale. The Crescent at upper right comes from a Wolf-Rayet star that shed its outer layers and is now driving a much faster wind into them, hard enough that the collision emits X-rays; that star has very little time left and will end as a supernova. The faint round bubble at lower left is the Soap Bubble Nebula, PN G75.5+1.7, the quiet death of a star closer to the Sun’s mass, and it wasn’t found by any survey: the amateur astrophotographer Dave Jurasevich picked it out of his own images in 2008. Both sit against the hydrogen of the Cygnus region, roughly 5,000 light-years away.
