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.

                                2019 August 4

                          Rumors of a Dark Universe
            Image Credit: High-Z Supernova Search Team, HST, NASA

   Explanation: Twenty-one years ago results were first presented
   indicating that most of the energy in our universe is not in stars or
   galaxies but is tied to space itself. In the language of cosmologists,
   a large cosmological constant -- dark energy -- was directly implied by
   new distant supernova observations. Suggestions of a cosmological
   constant were not new -- they have existed since the advent of modern
   relativistic cosmology. Such claims were not usually popular with
   astronomers, though, because dark energy was so unlike known universe
   components, because dark energy's abundance appeared limited by other
   observations, and because less-strange cosmologies without a signficant
   amount of dark energy had previously done well in explaining the data.
   What was exceptional here was the seemingly direct and reliable method
   of the observations and the good reputations of the scientists
   conducting the investigations. Over the two decades, independent teams
   of astronomers have continued to accumulate data that appears to
   confirm the existence of dark energy and the unsettling result of a
   presently accelerating universe. In 2011, the team leaders were awarded
   the Nobel Prize in Physics for their work. The featured picture of a
   supernova that occurred in 1994 on the outskirts of a spiral galaxy was
   taken by one of these collaborations.

             News: APOD is now available via Facebook in Hindi.
                     Tomorrow's picture: double eclipse
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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                             & Michigan Tech. U.

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