LL Pegasi Binary Star System Spiral Cloud in Pegasus | Hubble Space Telescope

LL Pegasi Binary Star System Spiral Cloud in Pegasus | Hubble Space Telescope

Although it looks like the pattern of a shell on the beach, this intriguing spiral is in fact astronomical in nature. This remarkable picture from the Advanced Camera for Surveys on the NASA/European Space Agency Hubble Space Telescope shows one of the most perfect geometrical forms created in space. It captures the formation of an unusual pre-planetary nebula, known as IRAS 23166+1655, around the star LL Pegasi (also known as AFGL 3068) in the constellation of Pegasus (the Winged Horse).

The striking picture shows what appears to be a thin spiral pattern of astonishingly regularity winding around the star that is itself hidden behind thick dust. The spiral pattern suggests a regular periodic origin for the nebula’s shape. The material forming the spiral is moving outwards a speed of about 50,000 km/hour and, by combining this speed with the distance between layers, astronomers calculate that the shells are each separated by about 800 years.

The spiral is thought to arise because LL Pegasi is a binary system with the star that is losing material and a companion star orbiting each other. The spacing between layers in the spiral is expected to directly reflect the orbital period of the binary, estimated to be also about 800 years.

The creation and shaping of planetary nebulae is an exciting area of stellar evolution. Stars with masses from about half that of the Sun up to about eight times that of the Sun do not explode as supernovae at the ends of their lives. Instead a more regal end awaits them as their outer layers of gas are shed and drift into space, creating striking and intricate structures that to Earth-bound observers often look like dramatic watercolor paintings. IRAS 23166+1655 is just starting this process and the central star has yet to emerge from the cocoon of enveloping dust.

Image Processor Judy Schmidt: "It's a spiral in space created by a pair of stars enshrouded by dust . . . We get a space spiral. It has no self-illumination in visible light, so it is being illuminated by the light from any nearby Mliky Way stars. The bright star does not necessarily have anything to do with the illumination even though it looks like it might. This is one of my favorite things ever."

Credit: European Space Agency (ESA)/NASA & R. Sahai
Image Processing: Judy Schmidt
Release Date: Jan. 4, 2018

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