Astronomy Picture of the Day

   [1]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.

                               2019 October 26
    [2]See Explanation. Clicking on the picture will download the highest
                        resolution version available.

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

   Explanation: [6]Albert Einstein's 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, [7]seen through the looking glass 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. [8]The arcs are optical images of
   distant background galaxies lensed by the foreground group's total
   distribution of gravitational mass. Of course, that gravitational mass
   is dominated [9]by dark matter. 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. [10]Curiouser about galaxy group mergers?
   The Cheshire Cat [11]group grins in the constellation Ursa Major, some
   4.6 billion light-years away.

                       Tomorrow's picture: ghostly sky
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    Authors & editors: [23]Robert Nemiroff ([24]MTU) & [25]Jerry Bonnell
                                 ([26]UMCP)
          NASA Official: Phillip Newman [27]Specific rights apply.
              [28]NASA Web Privacy Policy and Important Notices
                A service of: [29]ASD at [30]NASA / [31]GSFC
                           & [32]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://apod.nasa.gov/apod/image/1910/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. https://apod.nasa.gov/apod/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. https://apod.nasa.gov/apod/ap191025.html
  13. https://apod.nasa.gov/apod/archivepix.html
  14. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  15. https://apod.nasa.gov/apod/lib/aptree.html
  16. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  17. https://apod.nasa.gov/apod/calendar/allyears.html
  18. https://apod.nasa.gov/apod.rss
  19. https://apod.nasa.gov/apod/lib/edlinks.html
  20. https://apod.nasa.gov/apod/lib/about_apod.html
  21. http://asterisk.apod.com/discuss_apod.php?date=191026
  22. https://apod.nasa.gov/apod/ap191027.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. https://apod.nasa.gov/apod/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/