                        Astronomy Picture of the Day

    Discover the cosmos! Each day a different image or photograph of our
      fascinating universe is featured, along with a brief explanation
                    written by a professional astronomer.

                              2021 November 29

                    The Extraordinary Spiral in LL Pegasi
   Image Credit: NASA, ESA, Hubble, HLA; Processing & Copyright: Jonathan
                                    Lodge

   Explanation: What created the strange spiral structure on the upper
   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
   and 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.

                    Tomorrow's picture: planet with moons
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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