Spirograph in the sky

Some 2,000 light-years from Earth, an elderly star has ejected its puffy outer layers to form a luminous, jewel-like ball of gas. Set aglow by ultraviolet radiation pouring out from the core of the aging star, this gaseous nebula—called IC 418—resembles a “spirograph,” the pattern produced by the familiar drawing toy. The Hubble Space Telescope took pictures of the nebula last year, and NASA released the images on Sept. 7.

False-color view of the planetary nebula IC 418. Red denotes emission from ionized nitrogen, the coolest gas in the nebula. Green indicates emission from hydrogen, and blue the radiation from ionized oxygen, which is hottest and closest to the core. NASA/Hubble

Astronomers more than a century ago dubbed such gaseous structures planetary nebulae because their disk like shape, as discerned in the telescopes of the day, reminded the researchers of planets.

Over the next several thousand years, IC 418 will slowly disperse. The aging star then left behind—the remnant of a bloated star called a red giant—will collapse to become a white dwarf. It will take billions of years to completely cool and fade. Our sun will meet the same fate, but not for about 5 billion years.

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