  APOD: 2017 October 16 - GW170817: A Spectacular Multiradiation Merger Event
                                   Detected

                         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 16
        GW170817: A Spectacular Multi-Radiation Merger Event Detected
      Illustrative Video Credit: NASA [2] 's Conceptual Imaging Lab [3]

Explanation: Both gravitational and electromagnetic radiations have been
detected in rapid succession for an explosive merging event for the first
time. Data from the outburst fit well with a spectacular binary neutron-star
death-spiral. The explosive episode was seen on August 17 in nearby NGC 4993
[4] , an elliptical galaxy [5]  only 130 million light years [6]  distant.
Gravitational waves [7]  were seen first [8]  by the ground based LIGO [9]
and Virgo [10]  observatories, while seconds later the Earth-orbiting Fermi
[11]  observatory detected gamma-rays, and hours after that Hubble [12] and
other observatories detected light throughout the electromagnetic spectrum.
Pictured is an animated illustrative movie [13] of the event's likely
progenitors. The video depicts hot neutron star [14] s as they spiral in [15]
toward each other and emit gravitational radiation [16] . As they merge, a
powerful jet extends that drives the short-duration gamma-ray burst [17] ,
followed by clouds of ejecta and, over time, an optical supernova-type episode
called a kilonova [18] . This first coincident detection confirms that LIGO
events can be associated with short-duration gamma-ray bursts [19] . Such
powerful neutron star mergers are thought to have seeded the universe [20]
with many heavy nuclei [21]  including the iodine needed for life [22] and the
uranium and plutonium needed for nuclear fission power [23] . You may already
own a souvenir [24]  of one of these explosions -- they are also thought to be
the original creators [25]  of gold [26] .

  Note:  This APOD may be updated with links to published journal articles as
                                 they appear.
                    Tomorrow's picture: asteroid rings [27]

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    Authors & editors: Robert Nemiroff [39] (MTU [40] ) & Jerry Bonnell [41]
                                  (UMCP [42] )
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Site notes:
  [1] archivepix.html
  [2] https://www.nasa.gov/
  [3] https://svs.gsfc.nasa.gov/cilab/index.html
  [4] https://en.wikipedia.org/wiki/NGC_4993
  [5] ap100520.html
  [6] http://chandra.harvard.edu/photo/cosmic_distance.html
  [7] ap160207.html
  [8] ap160211.html
  [9] http://ligo.org/science/faq.php
  [10] http://www.virgo-gw.eu/
  [11] https://www.nasa.gov/content/fermi-gamma-ray-space-telescope
  [12] http://www.stsci.edu/hst/HST_overview
  [13] https://youtu.be/x_Akn8fUBeQ
  [14] ap110305.html
  [15] https://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=10543
  [16] https://en.wikipedia.org/wiki/Gravitational-wave_astronomy
  [17] http://adsabs.harvard.edu/abs/1989Natur.340..126E
  [18] https://en.wikipedia.org/wiki/Kilonova
  [19] https://en.wikipedia.org/wiki/Gamma-ray_burst#Short_gamma-ray_bursts
  [20]
http://blog.sdss.org/2017/01/09/origin-of-the-elements-in-the-solar-system/
  [21] ap160125.html
  [22] https://en.wikipedia.org/wiki/Iodine#Biological_role
  [23] https://www.eia.gov/energyexplained/index.cfm?page=nuclear_home
  [24]
https://i.pinimg.com/originals/a5/a1/ef/a5a1ef30ef2823212b60b507f1e9f04f.jpg
  [25] ap171015.html
  [26] https://schiffgold.com/wp-content/uploads/2015/12/ft-knox.jpg
  [27] ap171017.html
  [28] ap171015.html
  [29] archivepix.html
  [30] lib/apsubmit2015.html
  [31] lib/aptree.html
  [32] https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  [33] calendar/allyears.html
  [34] /apod.rss
  [35] lib/edlinks.html
  [36] lib/about_apod.html
  [37] http://asterisk.apod.com/discuss_apod.php?date=171016
  [38] ap171017.html
  [39] http://www.phy.mtu.edu/faculty/Nemiroff.html
  [40] http://www.phy.mtu.edu/
  [41] https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  [42] http://www.astro.umd.edu/
  [43] lib/about_apod.html#srapply
  [44] https://www.nasa.gov/about/highlights/HP_Privacy.html
  [45] https://astrophysics.gsfc.nasa.gov/
  [46] https://www.nasa.gov/
  [47] https://www.nasa.gov/centers/goddard/
  [48] http://www.mtu.edu/
