 APOD: 2017 October 23 - NGC 4993: The Galactic Home of an Historic Explosion

                         Astronomy Picture of the Day

    Discover the cosmos! [1] Each day a different image or photograph of our
 fascinating universe is featured, along with a brief explanation written by a
                           professional astronomer.

                                2017 October 23
                                      [2]
            NGC 4993: The Galactic Home of an Historic Explosion
                      Image Credit: NASA [3]  & ESA [4]

Explanation: That reddish dot -- it wasn't there before. It's the dot to the
upper left of galaxy NGC 4993 [5] 's center, do you see it? When scanning the
large field of possible locations of an optical counterpart to the
unprecedented gravitational wave event GW170817 [6]  in August, the appearance
of this fading dot [7]  quickly became of historic importance. It pinpointed
GW170817's exact location, thereby enabling humanity's major telescopes to
examine the first ever electromagnetic wave [8]  counterpart to a
gravitational wave [9]  event, an event giving strong evidence of being a
short gamma-ray burst [10] kilonova [11] , the element-forming explosion that
occurs after two neutron stars merge [12] . The featured image [13]  of
lenticular [14]  galaxy NGC 4993 by Hubble shows the fading dot [15]  several
days after it was discovered. Analyses [16] , continuing [17] , include the
physics of the explosion [18] , what heavy elements formed [19] , the
similarity of the speeds of gravitational radiation and light, and calibrating
a new method for determining [20]  the distance scale of our universe [21] .

   More on GW170817: Journal [22] articles [23] , data [24] , graphics [25]
                   Tomorrow's picture: elements of you [26]

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    Authors & editors: Robert Nemiroff [38] (MTU [39] ) & Jerry Bonnell [40]
                                  (UMCP [41] )
          NASA Official:  Phillip Newman Specific rights apply [42] .
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              A service of: ASD [44]  at NASA [45]  / GSFC [46]
                           & Michigan Tech. U. [47]
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Site notes:
  [1] archivepix.html
  [2] image/1710/NGC4993_Hubble_1365.jpg
  [3] https://www.nasa.gov/
  [4] http://www.esa.int/
  [5] https://en.wikipedia.org/wiki/NGC_4993
  [6] ap171016.html
  [7]
https://www.nytimes.com/2017/10/16/science/ligo-neutron-stars-collision.html
  [8] https://science.nasa.gov/ems
  [9] https://spaceplace.nasa.gov/gravitational-waves/en/
  [10]
https://science.nasa.gov/science-news/science-at-nasa/2008/20oct_briefmystery
  [11] https://en.wikipedia.org/wiki/Kilonova
  [12] ap171016.html
  [13] https://www.spacetelescope.org/news/heic1717/
  [14] https://en.wikipedia.org/wiki/Lenticular_galaxy
  [15] https://www.spacetelescope.org/images/heic1717c/
  [16] http://adsabs.harvard.edu/abs/2017arXiv171005834L
  [17]
http://catsanimals.com/wp-content/uploads/2014/02/
Cat-Using-Computer-520x325.jpg
  [18]
https://www.forbes.com/sites/startswithabang/2017/10/20/
seeing-one-example-of-merging-neutron-stars-raises-five-incredible-questions/
  [19] ap170924.html
  [20] https://arxiv.org/abs/1710.05832
  [21] https://apod.nasa.gov/debate/debate96.html
  [22] https://www.ligo.caltech.edu/page/detection-companion-papers
  [23] https://lco.global/~iarcavi/kilonovae.html
  [24] https://kilonova.space/
  [25]
https://www.facebook.com/pg/APOD.Sky/photos/
?tab=album&album_id=1244806732290210
  [26] ap171024.html
  [27] ap171022.html
  [28] archivepix.html
  [29] lib/apsubmit2015.html
  [30] lib/aptree.html
  [31] https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  [32] calendar/allyears.html
  [33] /apod.rss
  [34] lib/edlinks.html
  [35] lib/about_apod.html
  [36] http://asterisk.apod.com/discuss_apod.php?date=171023
  [37] ap171024.html
  [38] http://www.phy.mtu.edu/faculty/Nemiroff.html
  [39] http://www.phy.mtu.edu/
  [40] https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  [41] http://www.astro.umd.edu/
  [42] lib/about_apod.html#srapply
  [43] https://www.nasa.gov/about/highlights/HP_Privacy.html
  [44] https://astrophysics.gsfc.nasa.gov/
  [45] https://www.nasa.gov/
  [46] https://www.nasa.gov/centers/goddard/
  [47] http://www.mtu.edu/
