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The Eskimo Nebula, from the Hubble Telescope

Andrew Fruchter (STScI) et al., WFPC2, HST, NASA

Many celestial objects are fascinating not only for their usefulness in helping explain the workings of the cosmos, but also because they are visually dazzling. The Eskimo Nebula, in the constellation Gemini, is a perfect example.

Also known as the Clown or Clown Face Nebula, the Eskimo is a planetary nebula approximately 5,000 light years away. It is the remnant of a dying star similar in mass to our Sun, and serves as an excellent illustration of our Sun’s ultimate fate in about five billion years.

The Eskimo Nebula’s apparent magnitude – a measurement astronomers use to describe an object’s brightness as seen from Earth – is 9.1, making it more than 15 times fainter than the dimmest stars the average person can see with the unaided eye. Since it is faint, the Eskimo Nebula cannot be viewed without a telescope or binoculars. The small white point in the middle is a white dwarf star. Surrounding this is a bright bubble of material blowing away from the star, representing the Eskimo’s face. Surrounding this is the Eskimo’s parka, the darker halo of gases with finger-shaped filaments that resemble comets in the way their tails are being blown away from the white dwarf.

About 10,000 years ago, the Eskimo Nebula was just an average star, much like our Sun. It had been like that for about 10 billion years, plugging along in a steady state of nuclear fusion that saw the transformation in its core of hydrogen into helium. The pressure exerted by all this outward-streaming energy balanced the inward pull of gravity, keeping the star in equilibrium. Once the hydrogen supply in the core was exhausted, nuclear fusion ceased, leaving nothing to counteract the star’s own gravity. The helium core collapsed, which created energy and temperatures high enough to trigger the fusion of helium into carbon and oxygen.

While the core was going through this process, the outer hydrogen layers of the star expanded, transforming the star into a red giant (when our Sun finally becomes a red giant, it may expand all the way out to Earth.) Once the helium fusion ended, gravity again caused the star’s core to collapse. This second contraction didn’t create enough energy to trigger further nuclear reactions, so the core continued to collapse until it was about the size of Earth and became known as a white dwarf star.

Surrounding this white dwarf is a shell of helium and hydrogen gases known as a planetary nebula, though it has nothing to do with a planet. As with so many scientific terms, the name is a leftover from centuries ago when, through crude telescopes, the shell of gas resembled the spherical shape of a planet.

The Eskimo Nebula captivates us for several reasons, from its value in interpreting the evolution of stars, to its intrinsic natural beauty. It is but one example of the wonders of space.

Kevin Schindler is the Lowell Observatory historian.

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