    APOD: 2018 May 12 - A Plurality of Singularities at the Galactic Center

                         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.

                                  2018 May 12
                                      [2]
             A Plurality of Singularities at the Galactic Center
      Image Credit: NASA/CXC [3]  / Columbia Univ./ C. Hailey et al. [4]

Explanation: A recent informal poll found that astronomers don't yet have a
good collective noun [5]  for a group of black holes, but they need one. The
red circles in this Chandra Observatory X-ray image [6] identify a group of a
dozen black holes that are members of binary star systems. With 5 to 30 times
the mass of the Sun, the black hole binaries are swarming within about 3
light-years of the center of our galaxy [7] where the supermassive black hole
identified as Sagittarius A* (Sgr A*) resides. Yellow circles indicate X-ray
[8]  sources that are likely less massive neutron stars or white dwarf stars
in binary star systems. Alone, black holes [9] would be invisible, but as part
of a binary star system they accrete material from their normal companion star
and generate X-rays. At the distance of the galactic center Chandra can detect
only the brighter of these black hole binary systems as point-like sources of
X-rays, hinting that many fainter X-ray emitting black hole binaries should
exist there, as yet undetected [10] .

                Tomorrow's picture: volcano with lightning [11]

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    Authors & editors: Robert Nemiroff [23] (MTU [24] ) & Jerry Bonnell [25]
                                  (UMCP [26] )
          NASA Official:  Phillip Newman Specific rights apply [27] .
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                           & Michigan Tech. U. [32]
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Site notes:
  [1] archivepix.html
  [2] image/1805/sgra_swarm_sources.jpg
  [3] http://chandra.harvard.edu/
  [4] https://www.nature.com/articles/nature25029
  [5] https://www.latitudegroup.com/blog/collective-nouns/
  [6] http://chandra.harvard.edu/photo/2018/sgra_swarm/
  [7] ap180122.html
  [8] http://www.astronomycast.com/2009/05/ ep-135-x-ray-astronomy/
  [9] http://chandra.harvard.edu/learn_bh.html
  [10] https://arxiv.org/abs/1804.01543
  [11] ap180513.html
  [12] ap180511.html
  [13] archivepix.html
  [14] lib/apsubmit2015.html
  [15] lib/aptree.html
  [16] https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  [17] calendar/allyears.html
  [18] /apod.rss
  [19] lib/edlinks.html
  [20] lib/about_apod.html
  [21] http://asterisk.apod.com/discuss_apod.php?date=180512
  [22] ap180513.html
  [23] http://www.phy.mtu.edu/faculty/Nemiroff.html
  [24] http://www.phy.mtu.edu/
  [25] https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  [26] http://www.astro.umd.edu/
  [27] lib/about_apod.html#srapply
  [28] https://www.nasa.gov/about/highlights/HP_Privacy.html
  [29] https://astrophysics.gsfc.nasa.gov/
  [30] https://www.nasa.gov/
  [31] https://www.nasa.gov/centers/goddard/
  [32] http://www.mtu.edu/
