                        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.

                              2023 December 14

                       Supernova Remnant Cassiopeia A
        Image Credit: NASA, ESA, CSA, STScI; D. Milisavljevic (Purdue
    University), T. Temim (Princeton University), I. De Looze (University
                                  of Gent)

   Explanation: Massive stars in our Milky Way Galaxy live spectacular
   lives. Collapsing from vast cosmic clouds, their nuclear furnaces
   ignite and create heavy elements in their cores. After only a few
   million years for the most massive stars, the enriched material is
   blasted back into interstellar space where star formation can begin
   anew. The expanding debris cloud known as Cassiopeia A is an example of
   this final phase of the stellar life cycle. Light from the supernova
   explosion that created this remnant would have been first seen in
   planet Earth's sky about 350 years ago, although it took that light
   11,000 years to reach us. This sharp NIRCam image from the James Webb
   Space Telescope shows the still hot filaments and knots in the
   supernova remnant. The whitish, smoke-like outer shell of the expanding
   blast wave is about 20 light-years across, while the bright speck near
   center is a neutron star, the incredibly dense, collapsed remains of
   the massive stellar core. Light echoes from the massive star's
   cataclysmic explosion are also identified in Webb's detailed image of
   supernova remnant Cassiopeia A.

                         Tonight watch: The Geminids
                     Tomorrow's picture: stellar eclipse
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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