The Extraordinary Spiral in LL Pegasi

Explanation: What created the strange spiral structure on the left? No one is sure, although it is likely related to a star in a binary star system entering the planetary nebula phase, when its outer atmosphere is ejected. The huge spiral spans about a third of a light year across and, winding four or five complete turns, has a regularity that is without precedent. Given the expansion rate of the spiral gas, a new layer must appear about every 800 years, a close match to the time it takes for the two stars to orbit each other. The star system that created it is most commonly known as LL Pegasi , but also AFGL 3068. The unusual structure itself has been cataloged as IRAS 23166+1655 . The featured image was taken in near- infrared light by the Hubble Space Telescope . Why the spiral glows is itself a mystery, with a leading hypothesis being illumination by light reflected from nearby stars.