NGC 2818 is a planetary nebula about 6.5 light-years across, located some 10,400 light-years away in the southern constellation Pyxis.
The structure of NGC 2818 contains the glowing gaseous outer layers of the central sun-like star that were expelled into interstellar space during the final stages of its life, after it ran out of fuel to sustain the nuclear reactions in its core.
Planetary nebulae fade gradually over tens of thousands of years. The hot, remnant stellar core of NGC 2818 will eventually cool off for billions of years as a white dwarf. Our own Sun will undergo a similar process, so, this planetary nebula could well offer a glimpse of the future that awaits our own Sun in about five billion years.
NGC 2818 is often heralded as one of the Milky Way’s few planetary nebulae to be discovered as a member of an open star cluster (NGC 2818A). Recent investigations, however, suggest that it is merely a chance alignment, as the objects are actually located at varying distances along the line-of-sight. The case is just an example of a superposed pair.
Moreover, there has yet to be a single established case of a Galactic planetary nebula discovered in an open cluster. Planetary nebulae have been detected in several globular star clusters in our Milky Way. These densely-packed, gravitationally-bound groups of 100,000s to millions of stars are far older than their open cluster counterparts.
Theoretical models predict that planetary nebulae can form from main-sequence stars of between 8 and 1 solar masses, which puts their age at 40 million years and older.
The colors in the image of NGC 2818 represent a range of emissions coming from the clouds of the nebula: red represents nitrogen, green represents hydrogen, and blue represents oxygen.