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                        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.

                                2025 July 22
      A nearly circular nebula with two rings is shown. The outer ring
   appears orange while while the inner rings is more complex and appears
       blue. Please see the explanation for more detailed information.

                        A Double Detonation Supernova
    Image Credit: ESO, P. Das et al.; Background stars (NASA/Hubble): K.
                                 Noll et al.

   Explanation: Can some supernovas explode twice? Yes, when the first
   explosion acts like a detonator for the second. This is a leading
   hypothesis for the cause of supernova remnant (SNR) 0509-67.5. In this
   two-star system, gravity causes the larger and fluffier star to give up
   mass to a smaller and denser white dwarf companion. Eventually the
   white dwarf's near-surface temperature goes so high that it explodes,
   creating a shock wave that goes both out and in -- and so triggers a
   full Type Ia supernova near the center. Recent images of the SNR
   0509-67.5 system, like the featured image from the Very Large Telescope
   in Chile, show two shells with radii and compositions consistent with
   the double detonation hypothesis. This system, SNR 0509-67.5 is also
   famous for two standing mysteries: why its bright supernova wasn't
   noted 400 years ago, and why no visible companion star remains.

                  Tomorrow's picture: rock being vaporized
     __________________________________________________________________

       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
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