¿ 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 December 16 IFRAME: [2]https://www.youtube.com/embed/sau5-39wK1c?rel=0 Sonified: The Matter of the Bullet Cluster Image Credit: X-ray: NASA/CXC/SAO; Optical: NASA/STScI, Magellan/U.Arizona; Lensing Map: NASA/STScI, ESO WFI, Magellan/U.Arizona; Sonification: NASA/CXC/SAO/K.Arcand, SYSTEM Sounds (M. Russo, A. Santaguida) Explanation: What's the matter with the Bullet Cluster? This massive cluster of galaxies ([3]1E 0657-558) creates [4]gravitational lens distortions of background galaxies in a way that has been interpreted as strong evidence for the leading theory: that [5]dark matter exists within. [6]Different analyses, though, indicate that a less popular alternative -- modifying gravity-- could explain cluster dynamics without [7]dark matter, and provide a [8]more likely progenitor scenario as well. Currently, the [9]two scientific hypotheses are competing to explain the observations: it's [10]invisible matter versus amended gravity. The duel is dramatic as a clear [11]Bullet-proof example of dark matter would shatter the simplicity of [12]modified gravity theories. The [13]featured sonified image is a [14]Hubble/[15]Chandra/[16]Magellan composite with red depicting the X-rays emitted by hot gas, and blue depicting the suggested [17]separated dark matter distribution. The [18]sonification assigns low tones to dark matter, mid-range frequencies to [19]visible light, and high tones to [20]X-rays. The battle over the [21]matter in the Bullet cluster is likely to continue as more [22]observations, computer simulations, and analyses are completed. Submitted to APOD: [23]Notable images of the 2020 Geminids Meteor Shower Tomorrow's picture: open space __________________________________________________________________ [24]< | [25]Archive | [26]Submissions | [27]Index | [28]Search | [29]Calendar | [30]RSS | [31]Education | [32]About APOD | [33]Discuss | [34]> __________________________________________________________________ Authors & editors: [35]Robert Nemiroff ([36]MTU) & [37]Jerry Bonnell ([38]UMCP) NASA Official: Phillip Newman [39]Specific rights apply. [40]NASA Web Privacy Policy and Important Notices A service of: [41]ASD at [42]NASA / [43]GSFC & [44]Michigan Tech. U. References 1. https://apod.nasa.gov/apod/archivepix.html 2. https://www.youtube.com/embed/sau5-39wK1c?rel=0 3. https://en.wikipedia.org/wiki/Bullet_Cluster 4. https://apod.nasa.gov/apod/ap160722.html 5. https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy 6. https://ui.adsabs.harvard.edu/abs/2015MNRAS.454.3810M/abstract 7. https://medium.com/starts-with-a-bang/galaxy-clusters-prove-dark-matters-existence-fd962c979458 8. https://ui.adsabs.harvard.edu/abs/2010ApJ...718...60L/abstract 9. http://backreaction.blogspot.com/2017/01/the-bullet-cluster-as-evidence-against.html 10. http://chandra.harvard.edu/xray_astro/dark_matter/ 11. https://ui.adsabs.harvard.edu/abs/2015MNRAS.452.3030T/abstract 12. https://en.wikipedia.org/wiki/Alternatives_to_general_relativity 13. http://chandra.harvard.edu/photo/2006/1e0657/ 14. https://www.nasa.gov/mission_pages/hubble/story/index.html 15. https://www.nasa.gov/mission_pages/chandra/main/index.html 16. http://www.gmto.org/overview/ 17. http://funny-pics.co/wp-content/uploads/funny-cat-in-the-fence-picture-445x351.jpg 18. https://chandra.si.edu/photo/2020/sonify2/index.html 19. https://science.nasa.gov/ems/09_visiblelight 20. https://science.nasa.gov/ems/11_xrays 21. https://medium.com/starts-with-a-bang/the-bullet-cluster-proves-dark-matter-exists-but-not-for-the-reason-most-physicists-think-b6bc1320a21b 22. https://ui.adsabs.harvard.edu/abs/2015PhRvD..91j3524G/abstract 23. https://www.facebook.com/media/set/?vanity=APOD.Sky&set=a.3216897281747802 24. https://apod.nasa.gov/apod/ap201214.html 25. https://apod.nasa.gov/apod/archivepix.html 26. https://apod.nasa.gov/apod/lib/apsubmit2015.html 27. https://apod.nasa.gov/apod/lib/aptree.html 28. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search 29. https://apod.nasa.gov/apod/calendar/allyears.html 30. https://apod.nasa.gov/apod.rss 31. https://apod.nasa.gov/apod/lib/edlinks.html 32. https://apod.nasa.gov/apod/lib/about_apod.html 33. http://asterisk.apod.com/discuss_apod.php?date=201215 34. https://apod.nasa.gov/apod/ap201216.html 35. http://www.phy.mtu.edu/faculty/Nemiroff.html 36. http://www.phy.mtu.edu/ 37. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html 38. http://www.astro.umd.edu/ 39. https://apod.nasa.gov/apod/lib/about_apod.html#srapply 40. https://www.nasa.gov/about/highlights/HP_Privacy.html 41. https://astrophysics.gsfc.nasa.gov/ 42. https://www.nasa.gov/ 43. https://www.nasa.gov/centers/goddard/ 44. http://www.mtu.edu/