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. 2022 May 11 [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: pixels in space __________________________________________________________________ [12]< | [13]Archive | [14]Submissions | [15]Index | [16]Search | [17]Calendar | [18]RSS | [19]Education | [20]About APOD | [21]Discuss | [22]> __________________________________________________________________ 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/2205/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/ap220510.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=220511 22. https://apod.nasa.gov/apod/ap220512.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/