[In Depth] Paired stars sculpt nebulae into fanciful shapes
For decades, astronomers have suspected that planetary nebulae—dazzlingly colorful shrouds of gas cast off by dying stars—owe their weird but often symmetrical shapes to the sculpting magnetic forces of two stars orbiting each other at the nebula's center. Now, a study has helped confirm theorists' picture that many nebulae are the handiwork of binary stars in which the companions orbit each other so closely that they share the same atmosphere. There are more than a thousand known planetary nebulae, and few have the simple, spherical shape that would be expected from a solitary star expelling its outer layers in dying gasps. Instead, they often look like hourglasses or butterflies. The new study identifies eight star systems where the orbital axis for a binary pair lines up with the long axis of symmetry for the nebula—suggesting that theorists were right all along. Author: Joshua Sokol