                        Astronomy Picture of the Day

    Discover the cosmos! Each day a different image or photograph of our
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                    written by a professional astronomer.

                              2020 December 16

                 Sonified: The Matter of the Bullet Cluster
           Image Credit: X-ray: NASA/CXC/SAO; Optical: NASA/STScI,
            Magellan/U.Arizona; Lensing Map: NASA/STScI, ESO WFI,
   Magellan/U.Arizona; Sonification: NASA/CXC/SAO/K.Arcand, SYSTEM Sounds
                          (M. Russo, A. Santaguida)

   Explanation: What's the matter with the Bullet Cluster? This massive
   cluster of galaxies (1E 0657-558) creates gravitational lens
   distortions of background galaxies in a way that has been interpreted
   as strong evidence for the leading theory: that dark matter exists
   within. Different analyses, though, indicate that a less popular
   alternative -- modifying gravity-- could explain cluster dynamics
   without dark matter, and provide a more likely progenitor scenario as
   well. Currently, the two scientific hypotheses are competing to explain
   the observations: it's invisible matter versus amended gravity. The
   duel is dramatic as a clear Bullet-proof example of dark matter would
   shatter the simplicity of modified gravity theories. The featured
   sonified image is a Hubble/Chandra/Magellan composite with red
   depicting the X-rays emitted by hot gas, and blue depicting the
   suggested separated dark matter distribution. The sonification assigns
   low tones to dark matter, mid-range frequencies to visible light, and
   high tones to X-rays. The battle over the matter in the Bullet cluster
   is likely to continue as more observations, computer simulations, and
   analyses are completed.

    Submitted to APOD: Notable images of the 2020 Geminids Meteor Shower
                       Tomorrow's picture: open space
     __________________________________________________________________

       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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                             & Michigan Tech. U.

