NGC 5979, a planetary nebula in Triangulum Australe

NGC 5979, a planetary nebula in Triangulum Australe

Image Credit: ESA, ESO and NASA

NGC 5979 is a planetary nebula of a little over ⅔ of a light-year across, located some 11,700 light-years away from Earth in the southern constellation of Triangulum Australe (the Southern Triangle), while it is moving away from us at only about 23 kilometers per second.

Despite their name, planetary nebulae have nothing to do with planets. The name of planetary nebulae arose in the 18th century because of the visual similarity between some round planetary nebulae and the planets Uranus and Neptune when viewed through small optical telescopes. The name has stuck even though modern telescopes make it obvious that these objects are not planets at all, but the glowing gassy outer layers thrown off by a hot dying star.

A medium-sized star like our Sun spends most of its life quietly converting hydrogen into helium. However when the hydrogen in the stellar core is exhausted, 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.

Planetary nebulae last for only about 10,000 years, a fleeting episode in the 10-billion-year lifespan of Sun-like stars. So, over the next several thousand years, NGC 5979 will gradually disperse into space, and then the white dwarf, HD 140586, 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.

This colour image is taken with the Wide Field Planetary Camera 2 onboard the Hubble Space Telescope. It is a composite of raw FITS files made with the ESA/ESO/NASA Photoshop FITS Liberator. The image was composed from four individual exposures taken through: A blue narrow-band filter (502 nm, 460 seconds), a green wide-band filter (555 nm, 240 seconds), an orange-red narrow-band filter (658 nm, 1200 seconds), and a red, or near-infrared, wide-band filter (814 nm, 480 seconds).

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