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The Skull Nebula is well named. It’s the stripped-off “skin” of a once-impressive star. All that remains of the star is its dying core.
The nebula is about 1600 light-years away, in the constellation Cetus. It began forming about 6600 years ago as seen from Earth. The star, which was about four times as massive as the Sun, could no longer produce nuclear reactions in its core. The core began collapsing to form a white dwarf — a small, dense ball of carbon and oxygen. It continues to shine, though, because it’s extremely hot.
As the core collapsed, the star’s outer layers were blown off into space. Today, that gas is energized by the hot core, making it glow. Through a small telescope, the nebula resembles a skull. It spans several light-years. It’s continuing to expand, though. And over the millennia, the gas will spread out so much that the nebula will fade away.
The system actually consists of three stars. The other two are still in the prime of life. But they’re much less massive than the star that created the nebula, so they’re cool and faint.
And like the nebula, they’re spreading out. As the main star began losing mass, the attraction between the stars weakened. Today, the companions probably are about three times farther from the white dwarf than when the system was born.
The Skull Nebula is in the south at nightfall, to the lower left of bright orange Mars. But you need a telescope to see the ghostly grin of the Skull.
Script by Damond Benningfield