Andromeda Galaxy – A Spiral with a Hidden Intruder

Andromeda (M31) is the nearest large spiral galaxy to the Milky Way and the dominant member 
of the Local Group. With over 120 hours of integration, this observation reveals the extended 
structure of its spiral arms and the faint complexity of its outer regions. 

Beyond the galaxy itself, this field contains a rare and unexpected foreground object: SDSO1. 

SDSO1 is not associated with Andromeda. It is a large bow shock nebula within our own galaxy, 
formed from the remnant of the planetary nebula surrounding the symbiotic star EG 
Andromedae. The interaction between this fast-moving system and the interstellar medium 
produces a bright shock front, most prominent in doubly ionized oxygen (OIII), and a trailing 
structure extending over 45 parsecs. 

This object represents what is now referred to as a “ghost planetary nebula” phase. While the 
central star has faded, its supersonic motion continues to drive the bow shock forward, leaving 
behind a persistent and evolving structure that cuts across the distant light of Andromeda. 
This alignment, where a local stellar remnant overlays a neighboring galaxy, offers a rare 
multi-scale perspective, connecting stellar death within the Milky Way to galactic structure 
beyond it. 

Total Integration Time: 120 Hours 

Captured from Al Sadeem Observatory by Al Sadeem Astronomy