jan 032014

January 3, 2013 

The Eskimo Nebula, a planetary nebula in Gemini

NGC 2392, the Clownface Nebula

Image Credit: NASA, Andrew Fruchter and the ERO Team [Sylvia Baggett and Zoltan Levay (STScI), and Richard Hook (ST-ECF)]

The Eskimo Nebula (NGC 2392, and sometimes also called the Clownface Nebula) is a bipolar double-shell planetary nebula of about 0.68 light-year across, located over 2,870 light-years away from Earth in the constellation of Gemini (the Twins).

Planetary nebulae are not related to planets at all. The term is simply a historic relic since these (often round) objects looked like planets to astronomers in earlier times looking through small optical telescopes. When a star with a mass similar to that of our own Sun nears the end of its lifetime, it expands in size to become a red giant – an event our Sun will go through in about five billion years.

Eventually, the outer layers of the star (collapsing from a red giant to a white dwarf) are carried away by a 50,000 kilometer per hour wind, leaving behind a hot core. This hot core has a surface temperature of about 50,000 degrees Celsius, and is ejecting its outer layers in a much faster wind traveling six million kilometers per hour. The radiation from the hot star and the interaction of its fast wind with the slower wind creates the complex and filamentary shell of a planetary nebula.

Planetary nebulae fade gradually over tens of thousands of years while the hot, remnant stellar core will cool off for billions of years as a white dwarf. Since our own Sun will undergo a similar process, planetary nebulae could well offer a glimpse of the future that awaits our own Sun.

The Eskimo Nebula’s shape is created only about 10,000 years ago by a ring of dense material around the dying star’s equator, ejected during its red giant phase. When viewed through ground-based telescopes, it resembles a face surrounded by a fur parka hood, but from space the nebula displays complex gas clouds composed of the outer layers of a Sun-like star.

The Eskimo’s “face” contains some fascinating bubbles of matter and filaments, blown into space by the central star’s 1.5-million-kilometer-per-hour stellar “wind” of high-speed particles. One bubble lies in front of the other, obscuring part of the second lobe. The bubbles are not smooth like balloons but have filaments of denser matter.

The “parka hood” is a broad disk of material, plodding along at 115,000 kilometers per hour, preventing high-velocity stellar winds from pushing matter along the equator. It contains long, orange, comet-shaped objects, with their tails streaming away from the central dying star, possibly formed from a collision of slow-and fast-moving gases.

Chandra data have recently shown that the Eskimo Nebula has unusually high levels of X-ray emission. This leads researchers to deduce that there is an unseen companion to the hot central star. The interaction between a pair of binary stars could explain the elevated X-ray emission found there.

The Eskimo Nebula is easily located about midway between the stars Kappa and Lambda Geminorum, about 1° southeast of the wide double star 63 Geminorum. With low power it is an unimpressive sight, appearing to be little more than a star surrounded by dim haze. However, increased magnification and a little patience bring out some interesting details.

The image was taken on January 10 and 11, 2000, with the Wide Field and Planetary Camera 2 on the Hubble Space Telescope. The nebula’s glowing gases produce the colors in this image: nitrogen (red), hydrogen (green), oxygen (blue), and helium (violet).

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