                        Astronomy Picture of the Day

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                               2021 November 2

               SN Requiem: A Supernova Seen Three Times So Far
   Image Credit: NASA, ESA, Hubble; Data: S. A. Rodney (U. South Carolina)
               et al.; Image Processing: J. DePasquale (STScI)

   Explanation: We've seen this same supernova three times -- when will we
   see it a fourth? When a distant star explodes in a supernova, we're
   lucky if we see it even once. In the case of AT 2016jka ("SN Requiem"),
   because the exploding star happened to be lined up behind the center of
   a galaxy cluster (MACS J0138 in this case), a comparison of Hubble
   Space Telescope images demonstrate that we saw it three times. These
   three supernova images are highlighted in circles near the bottom of
   the left frame taken in 2016. On the right frame, taken in 2019, the
   circles are empty because all three images of the single supernova had
   faded. Computer modeling of the cluster lens, however, indicates that a
   fourth image of the same supernova should eventually appear in the
   upper circle on the right image. But when? The best models predict this
   will happen in 2037, but this date is uncertain by about two years
   because of ambiguities in the mass distribution of the cluster lens and
   the brightness history of the stellar explosion. With refined
   predictions and vigilant monitoring, Earthlings living 16 years from
   now may be able to catch this fourth image -- and perhaps learn more
   about both galaxy clusters and supernovas at once.

   Discovery + Outreach: Graduate student research position open for APOD
                 Tomorrow's picture: Orange Horse and Flame
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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