The European Southern Observatory published this image on March 6, 2017. It’s a double star system, consisting of the star LL Pegasi (aka AFGL 3068) and a companion star. The image – from the Atacama Large Millimeter/submillimeter Array (ALMA) in northern Chile – shows a huge spiral some third of a light-year across. The secret to the spiral is a nebula, or cloud of gas, surrounding the two stars. In fact, LL Pegasi is an old star, moving into what’s called the planetary nebula phase. Planetary nebulae are vast shells of gas sloughed off older stars as they age and begin to die. In the case of this double system, the two stars are creating the spiral pattern as they orbit each other. Astronomers estimate that a new layer in the spiral must appear about every 800 years, a close match to the time it takes for the two stars to orbit each other.
The video below compares the observed structure surrounding LL Pegasi with a predicted theoretical model.
And, by the way, that first image on the video – also seen below – is another beautiful image of this system, taken in near-infrared light by the Hubble Space Telescope.
Bottom line: A double star system – consisting of LL Pegasi and companion star – orbit within a shell of gas. As they orbit, they create a spiral-shaped nebula.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.