jul 302013

July 30, 2013

The Fetus Nebula, a planetary nebula in Cygnus

NGC 7008

Image Credit & Copyright: Don Goldman, Astrodon Imaging (http://www.astrodonimaging.com) in collaboration with Dietmar Hagar (http://www.stargazer-observatory.com) and Paul Mortfield (http://www.backyardastronomer.com)

The Fetus Nebula (NGC 7008) is a planetary nebula of about 1.3 light-year across, located some 2,800 light-years away from Earth in the northern constellation of Cygnus (the Swan). It is approaching us at approximately 75.7 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.

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. Planetary nebulae can show complex structures, as the ejection of mass from the star is uneven in both time and direction.

They 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, the Fetus 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 different layers are probably due to two different outflows of gas and dust by the central star, which is in fact a binary system. Even amateur telescopes can easily resolve out this central white dwarf star and bright areas in the outer shell.

This image, that includes an unrelated gold and blue binary star system – known as HJ 1606 – just below the Fetus Nebula, was created by the combination of broad band and narrow band images from two different telescopes, on different dates in 2008.

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