                        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.

                                 2022 May 28

                    RCW 86: Historical Supernova Remnant
                    Image Credit & Copyright: Martin Pugh

   Explanation: In 185 AD, Chinese astronomers recorded the appearance of
   a new star in the Nanmen asterism. That part of the sky is identified
   with Alpha and Beta Centauri on modern star charts. The new star was
   visible for months and is thought to be the earliest recorded
   supernova. This deep image shows emission nebula RCW 86, understood to
   be the remnant of that stellar explosion. The narrowband data trace gas
   ionized by the still expanding shock wave. Space-based images indicate
   an abundance of the element iron and lack of a neutron star or pulsar
   in the remnant, suggesting that the original supernova was Type Ia.
   Unlike the core collapse supernova explosion of a massive star, a Type
   Ia supernova is a thermonuclear detonation on a a white dwarf star that
   accretes material from a companion in a binary star system. Near the
   plane of our Milky Way galaxy and larger than a full moon on the sky
   this supernova remnant is too faint to be seen by eye though. RCW 86 is
   some 8,000 light-years distant and around 100 light-years across.

                 Tomorrow's picture: a galaxy cluster forms
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