A hollow star, adrift in its own light
NGC 2438 is a planetary nebula in the constellation Puppis, the expanding remains of a Sun-like star that shed its outer layers near the end of its life. At its center lies the exposed stellar core, now illuminating the surrounding gas from within and carving out the bright, circular cavity that defines the nebula’s striking form.
The luminous inner shell is dominated by oxygen emission, giving the nebula its cool cyan glow, while the surrounding envelope is traced by hydrogen, forming a faint red halo that marks the outer boundary of the ejected material. This layered structure is not decorative—it is a physical record of successive mass-loss episodes as the star transitioned from a red giant to a compact stellar remnant.
What makes NGC 2438 particularly compelling is the contrast between its sharply defined interior and its extremely delicate outer halo. The inner ring appears almost suspended in space, while the diffuse envelope fades gradually into the surrounding star field, revealing the true scale of the outflow and the gentle, expanding geometry of the nebula. The result is an object that feels both precise and ephemeral: a symmetrical core embedded within a tenuous, slowly dispersing shell.
NGC 2438 is often seen projected against the open cluster M46, but it is not physically associated with it. Instead, it stands alone in the foreground—a solitary stellar relic whose light continues to shape and illuminate the material it cast off thousands of years ago.
Imaged in Ha OIII RGB OTA RiDK 700 at Observatorio El Sauce, Chile.
Image acquisition and processing: Mike Selby