Image Credit: ESO
The Fine Ring Nebula (also known as Shapley 1 (Sp 1) after its discoverer Harlow Shapley, or PLN 329+2.1) is an unusual ring-shaped planetary nebula that lies some 1000 light-years from Earth in the southern constellation of Norma.
Despite their name, planetary nebulae have nothing to do with planets. The name of planetary nebulae arose because of the visual similarity between some round planetary nebulae and the planets Uranus and Neptune when viewed through early telescopes.
When a star with a mass up to eight times that of the Sun runs out of fuel at the end of its life, it blows off its outer shells and begins to lose mass. This allows the hot, inner core of the star (collapsing from a red giant to a white dwarf) to radiate strongly, causing this outward-moving cocoon of gas to glow brightly.
Over the next several thousand years, the nebula will gradually disperse into space, and then the white dwarf will cool and fade away for billions of years. Our own Sun is expected to undergo a similar fate, but fortunately this will not occur until some 5 billion years from now.
The Fine Ring Nebula is unusual in the way that most planetary nebulae are either spherical or elliptical in shape, or bipolar (featuring two symmetric lobes of material). But the Fine Ring Nebula looks like an almost perfect circular ring with a faint outer halo.
These ring-shaped planetary nebulae are formed when the progenitor star is actually a binary system. The interaction between the primary star and its orbiting companion shapes the ejected material. The Fine Ring Nebula’s central magnitude 14 central white dwarf star, of about one-third of a light-year across, forms indeed a close-binary system with a companion star, orbiting each other with a period of 2.9 days.
Observations suggest that the binary pair is almost perfectly face-on from our vantage point, implying that the planetary nebula’s structure is aligned in the same way. We are looking down on a torus (doughnut shape) of ejected material, leading to the circular ring shape in the image.
Not only can these planetary nebulae be admired for their beauty, but the study of precisely how they form their shapes is a fascinating topic in astronomical research.
This image was captured by the Faint Object Spectrograph and Camera mounted on the New Technology Telescope at the La Silla Observatory in Chile using multiple filters: light observed through B and O-III filters is shown in blue,