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 November 4

                 Fifty Gravitational Wave Events Illustrated
    Image Credit: LIGO Virgo Collaborations, Frank Elavsky, Aaron Geller,
                               Northwestern U.

   Explanation: Over fifty gravitational wave events have now been
   detected. These events mark the distant, violent collisions of two
   black holes, a black hole and a neutron star, or two neutron stars.
   Most of the 50 events were detected in 2019 by the LIGO gravitational
   wave detectors in the USA and the VIRGO detector in Europe. In the
   featured illustration summarizing the masses of the first 50 events,
   blue dots indicate higher-mass black holes while orange dots denote
   lower-mass neutron stars. Astrophysicists are currently uncertain,
   though, about the nature of events marked in white involving masses
   that appear to be in the middle -- between two and five solar masses.
   The night sky in optical light is dominated by nearby and bright
   planets and stars that have been known since the dawn of humanity. In
   contrast, the sky in gravitational waves is dominated by distant and
   dark black holes that have only been known about for less than five
   years. This contrast is enlightening -- understanding the gravitational
   wave sky is already reshaping humanity's knowledge not only of star
   birth and death across the universe, but properties of the universe
   itself.

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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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                      A service of: ASD at NASA / GSFC
                             & Michigan Tech. U.

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