66 ASTRONOMY • DECEMBER 2021
BREAKTHROUGH
TWO STARS FORGE A DIAMOND NECKLACE
The aptly named Necklace Nebula dazzles from 15,000 light-years away. This planetary nebula started developing some
10,000 years ago from two closely orbiting stars. As the more massive component neared the end of its life, it expanded and
quickly enveloped its companion. The smaller sun didn’t flinch, however, and began to transfer its orbital angular momentum
to the swollen star’s rotation. When the giant’s gravity could no longer hold on to its fast-moving outer layers, they spun off.
The densest clumps of ejected debris created the necklace’s sparkling “diamonds.” Just a few million miles now separate the
dying star’s core from the companion sun — too close for even the Hubble Space Telescope to split them. ESA/HUBBLE & NASA/K. NOLL