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. 2020 May 15 [2]See Explanation. Clicking on the picture will download the highest resolution version available. Galaxy Wars: M81 and M82 Image Credit & [3]Copyright: [4]Dietmar Hager, [5]Torsten Grossmann Explanation: These two galaxies are far far away, 12 million light-years distant toward the northern constellation of the Great Bear. On the left, with grand spiral arms and bright yellow core is spiral galaxy [6]M81, some 100,000 light-years across. On the right marked by red gas and dust clouds, is irregular galaxy [7]M82. The pair have been locked in gravitational combat for a billion years. [8]Gravity from each galaxy has profoundly affected the other during a series of cosmic close encounters. Their last go-round lasted about 100 million years and likely raised density waves rippling around M81, resulting in the richness of [9]M81's spiral arms. [10]M82 was left with violent star forming regions and colliding gas clouds so energetic the galaxy glows in X-rays. In the next few billion years, their continuing gravitational encounters will result in a merger, and a [11]single galaxy will remain. Tomorrow's picture: light-weekend __________________________________________________________________ [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/2005/M81-82.jpg 3. https://apod.nasa.gov/apod/lib/about_apod.html#srapply 4. http://www.stargazer-observatory.com/ 5. http://astrogrossi.de/ 6. https://apod.nasa.gov/apod/ap190417.html 7. https://apod.nasa.gov/apod/ap190723.html 8. https://phys.org/news/2019-11-astronomers-stellar-halo.html 9. http://www.youtube.com/watch?v=0seVq5ydqzk 10. https://hubblesite.org/contents/news-releases/2001/news-2001-08.html 11. https://science.nasa.gov/science-news/science-at-nasa/2012/31may_andromeda/ 12. https://apod.nasa.gov/apod/ap200514.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=200515 22. https://apod.nasa.gov/apod/ap200516.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/