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. 2023 June 15 [2]See Explanation. Clicking on the picture will download the highest resolution version available. M15: Dense Globular Star Cluster Image Credit: [3]NASA, [4]ESA, [5]Hubble Legacy Archive; Processing: [6]Ehsan Ebrahimian Explanation: [7]Messier 15 is an immense swarm of over 100,000 stars. A 13 billion year old relic of the early formative years of our galaxy it's one of about 170 globular star clusters that still roam the halo of the Milky Way. Centered in this sharp [8]reprocessed Hubble image, M15 lies some 35,000 light-years away toward the constellation Pegasus. Its diameter is about 200 light-years, but more than half its stars are packed into the central 10 light-years or so, making one of the densest concentrations of stars known. [9]Hubble-based measurements of the increasing velocities of M15's central stars are evidence that a massive black hole resides at the center of the dense cluster. M15 is also known to [10]harbour a planetary nebula. Called Pease 1 (aka PN Ps 1), it can be seen in this image as a small blue blob below and just right of center. Tomorrow's picture: when time lapses __________________________________________________________________ [11]< | [12]Archive | [13]Submissions | [14]Index | [15]Search | [16]Calendar | [17]RSS | [18]Education | [19]About APOD | [20]Discuss | [21]> __________________________________________________________________ Authors & editors: [22]Robert Nemiroff ([23]MTU) & [24]Jerry Bonnell ([25]UMCP) NASA Official: Phillip Newman [26]Specific rights apply. [27]NASA Web Privacy Policy and Important Notices A service of: [28]ASD at [29]NASA / [30]GSFC & [31]Michigan Tech. U. References 1. https://apod.nasa.gov/apod/archivepix.html 2. https://apod.nasa.gov/apod/image/2306/M15-3.jpg 3. https://www.nasa.gov/ 4. https://www.esa.int/ 5. https://hla.stsci.edu/ 6. https://www.instagram.com/anugrafy/ 7. https://www.nasa.gov/feature/goddard/2017/messier-15 8. https://www.instagram.com/p/CtL-6FgNc5l/ 9. https://arxiv.org/abs/astro-ph/0209314 10. https://ui.adsabs.harvard.edu/abs/2020AJ....159..276B/abstract 11. https://apod.nasa.gov/apod/ap230614.html 12. https://apod.nasa.gov/apod/archivepix.html 13. https://apod.nasa.gov/apod/lib/apsubmit2015.html 14. https://apod.nasa.gov/apod/lib/aptree.html 15. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search 16. https://apod.nasa.gov/apod/calendar/allyears.html 17. https://apod.nasa.gov/apod.rss 18. https://apod.nasa.gov/apod/lib/edlinks.html 19. https://apod.nasa.gov/apod/lib/about_apod.html 20. http://asterisk.apod.com/discuss_apod.php?date=230615 21. https://apod.nasa.gov/apod/ap230616.html 22. http://www.phy.mtu.edu/faculty/Nemiroff.html 23. http://www.phy.mtu.edu/ 24. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html 25. http://www.astro.umd.edu/ 26. https://apod.nasa.gov/apod/lib/about_apod.html#srapply 27. https://www.nasa.gov/about/highlights/HP_Privacy.html 28. https://astrophysics.gsfc.nasa.gov/ 29. https://www.nasa.gov/ 30. https://www.nasa.gov/centers/goddard/ 31. http://www.mtu.edu/