CG4 is a so-called cometary globule in Puppis. Cometary globules have superficial resemblance to comets, at least visually. They are relatively small areas of gas/dust in our Milky Way that frequently give birth to stars. This one takes the form of a head/face seen on profile, giving the impression that it is trying to “eat” the galaxy towards the left side of the frame. Of course, this galaxy (PGC 21338) is merely near CG4 in the 2 dimensions of RA and Dec — it is actually millions of light years more distant.
Technical details as follows:
RCOS 16″ @ f/11.3; Apogee U9; Planewave 200HR; LRGB with 8 hours Lum, 8 hours Red, 3 hours Green and 4 hours Blue; processed with Maxim, Registar, Neat Image, Photoshop, and PixInsight; SSRO @ CTIO, Chile; data acquired in January 2012.