                        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.

                               2021 December 7

             Ninety Gravitational Wave Spectrograms and Counting
     Image Credit: NSF, LIGO, VIRGO, KAGRA, Georgia Tech, Vanderbilt U.;
                   Graphic : Sudarshan Ghonge & Karan Jani

   Explanation: Every time two massive black holes collide, a loud
   chirping sound is broadcast out into the universe in gravitational
   waves. Humanity has only had the technology to hear these unusual
   chirps for the past seven years, but since then we have heard about 90
   -- during the first three observing runs. Featured above are the
   spectrograms -- plots of gravitational-wave frequency versus time -- of
   these 90 as detected by the giant detectors of LIGO (in the USA), VIRGO
   (in Europe), and KAGRA (in Japan). The more energy received on Earth
   from a collision, the brighter it appears on the graphic. Among many
   science firsts, these gravitational-radiation chirps are giving
   humanity an unprecedented inventory of black holes and neutron stars,
   and a new way to measure the expansion rate of our universe. A fourth
   gravitational wave observing run with increased sensitivity is
   currently planned to begin in 2022 December.

                       Tomorrow's picture: comet tails
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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.

