                        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.

                               2020 August 25

                 Visualization: A Black Hole Accretion Disk
      Visualization Credit: NASA's Goddard Space Flight Center, Jeremy
                                 Schnittman

   Explanation: What would it look like to circle a black hole? If the
   black hole was surrounded by a swirling disk of glowing and accreting
   gas, then the great gravity of the black hole would deflect light
   emitted by the disk to make it look very unusual. The featured animated
   video gives a visualization. The video starts with you, the observer,
   looking toward the black hole from just above the plane of the
   accretion disk. Surrounding the central black hole is a thin circular
   image of the orbiting disk that marks the position of the photon sphere
   -- inside of which lies the black hole's event horizon. Toward the
   left, parts of the large main image of the disk appear brighter as they
   move toward you. As the video continues, you loop over the black hole,
   soon looking down from the top, then passing through the disk plane on
   the far side, then returning to your original vantage point. The
   accretion disk does some interesting image inversions -- but never
   appears flat. Visualizations such as this are particularly relevant
   today as black holes are being imaged in unprecedented detail by the
   Event Horizon Telescope.

                     Tomorrow's picture: swan and galaxy
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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