                     APOD: 2017 August 5 - Gravity s Grin

                         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 August 5
                                      [2]
                                Gravity's Grin
    Image Credit: X-ray - NASA / CXC [3]  / J. Irwin et al. [4]  ; Optical -
                                NASA/STScI [5]

Explanation: Albert Einstein's [6] general theory of relativity, published
over 100 years ago, predicted the phenomenon of gravitational lensing. And
that's what gives these distant galaxies such a whimsical appearance, seen
through the looking glass [7]  of X-ray and optical image data from the
Chandra and Hubble space telescopes. Nicknamed the Cheshire Cat galaxy group,
the group's two large elliptical galaxies are suggestively framed by arcs. The
arcs are optical images [8] of distant background galaxies lensed by the
foreground group's total distribution of gravitational mass. Of course, that
gravitational mass is dominated by dark matter [9] . The two large elliptical
"eye" galaxies represent the brightest members of their own galaxy groups
which are merging. Their relative collisional speed of nearly 1,350
kilometers/second heats gas to millions of degrees producing the X-ray glow
shown in purple hues. Curiouser [10]  about galaxy group mergers? The Cheshire
Cat group grins [11] in the constellation Ursa Major, some 4.6 billion
light-years away.

                  Tomorrow's picture: exploding meteor [12]

-------------------------------------------------------------------------------
< [13] | Archive [14] | Submissions [15] | Index [16] | Search [17] | Calendar
  [18] | RSS [19] | Education [20] | About APOD [21] | Discuss [22] | > [23]
-------------------------------------------------------------------------------

    Authors & editors: Robert Nemiroff [24] (MTU [25] ) & Jerry Bonnell [26]
                                  (UMCP [27] )
          NASA Official:  Phillip Newman Specific rights apply [28] .
              NASA Web Privacy Policy and Important Notices [29]
              A service of: ASD [30]  at NASA [31]  / GSFC [32]
                           & Michigan Tech. U. [33]
----------
Site notes:
  [1] archivepix.html
  [2] image/1708/cheshirecat_chandra_complg.jpg
  [3] http://chandra.harvard.edu/
  [4] http://arxiv.org/abs/1505.05501
  [5] http://www.stsci.edu/
  [6] https://en.wikipedia.org/wiki/
List_of_scientific_publications_by_Albert_Einstein
  [7] http://chandra.harvard.edu/photo/2015/cheshirecat/
  [8] ap111221.html
  [9] https://www.lsst.org/science/dark-matter
  [10] http://arxiv.org/abs/1505.05501
  [11] http://www.gutenberg.org/files/11/11-h/11-h.htm
  [12] ap170806.html
  [13] ap170804.html
  [14] archivepix.html
  [15] lib/apsubmit2015.html
  [16] lib/aptree.html
  [17] http://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  [18] calendar/allyears.html
  [19] /apod.rss
  [20] lib/edlinks.html
  [21] lib/about_apod.html
  [22] http://asterisk.apod.com/discuss_apod.php?date=170805
  [23] ap170806.html
  [24] http://www.phy.mtu.edu/faculty/Nemiroff.html
  [25] http://www.phy.mtu.edu/
  [26] http://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  [27] http://www.astro.umd.edu/
  [28] lib/about_apod.html#srapply
  [29] http://www.nasa.gov/about/highlights/HP_Privacy.html
  [30] http://astrophysics.gsfc.nasa.gov/
  [31] http://www.nasa.gov/
  [32] http://www.nasa.gov/centers/goddard/
  [33] http://www.mtu.edu/
