NGC 6781¹ is a planetary nebula approximately 460 parsecs² (1,500 light years) from the Earth.  It is located in the constellation Aquila¹.  A planetary nebula is formed when an intermediate sized star uses up its supply of nuclear fuel³.  These stars do not have enough mass to end their lives in a spectacular super nova explosion³, however; as their cores collapse they expel their outer layers of stellar matter in expanding shells of gas leaving only an earth-sized, extremely hot, core³ known as a white dwarf star⁴.  The hot white dwarf radiates intense levels of ultraviolet light.  This radiation excites the surrounding shells of gas causing them to glow in the colors we observe.

NGC 6781 is believed to be a barrel-shaped object and is oriented such that we view it looking down the barrel's axis¹.  This gives the nebula a "ring shaped" appearance.  The nebula will continue to expand until it becomes too diffused to be visible.  The central white dwarf star is relatively dim and shines at a magnitude of 16.88.  Without nuclear fuel, it will cool and very gradually, over eons of time, fade away.

The image above was captured using Ha (Hydrogen Alpha) and OIII (Doubly Ionized Oxygen) narrowband filters.  The image was assembled by mapping Ha to red and OIII to green and blue.  The stars were overlaid with RGB filtered data to give them a near true color appearance.