Although it looks like the pattern of a shell on the beach, this intriguing spiral is in fact astronomical in nature. The Atacama Large Millimeter/submillimeter Array (ALMA) captured this remarkable image of a binary star system, where two stars — LL Pegasi and its companion — are locked in a stellar waltz, orbiting around their common centre of gravity. The old star LL Pegasi is continuously losing gaseous material as it evolves into a planetary nebula, and the distinct spiral shape is the imprint made by the stars orbiting in this gas. The spiral spans light-years and winds around with extraordinary regularity. Based on the expansion rate of the spiralling gas, astronomers estimate that a new “layer” appears every 800 years — approximately the same time it takes for the two stars to complete one orbit around each other. LL Pegasi was first highlighted about 10 years ago when the NASA/ESA Hubble Space Telescope obtained a picture of the almost-perfect spiral structure. This was the first time a spiral pattern had been found in material surrounding an old star. Now, ALMA’s observations, of which this image only shows one “cross-section”, have added an extra dimension to reveal the exquisitely-ordered 3D geometry of the spiral pattern. A full view of the 3D video can be seen in this video. An additional image shows a composition of the ALMA and Hubble data. Links: ALMA and Hubble observe LL Pegasi 3D view of LL Pegasi

Eye On The Sky: the top astro images of 2017

The top astro images released in 2017, as picked by BBC Sky at Night Magazine.

Try out a subscription to BBC Sky At Night Magazine and pay just £9.99 for 6 issues today!

Iain Todd

Published: October 2, 2017 at 11:00 am

Each month inBBC Sky at Night Magazinewe present our favourite images captured by the world's biggest and most hardworking telescopes for ourEye On The Sky image gallery.

Here we present a month-by-month selection of the most amazing astrophotos that made our monthly galleries in 2017.