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Messier 22 or M22, also known as NGC 6656, is an elliptical globular cluster of stars in the constellation Sagittarius, near the Galactic bulge region. It is one of the brightest globulars that is visible in the night sky. The brightest stars are 11th magnitude, with hundreds of stars bright enough to resolve with an 8" telescope. M22 is located just south of the Ecliptic, and northwest of Lambda Sagittarii (Kaus Borealis), the northernmost star of the "Teapot" asterism.
M22 was one of the first globulars to be discovered, on August 26, 1665 by Abraham Ihle and it was included in Charles Messier's catalog of comet-like objects on June 5, 1764. It was one of the first globular clusters to be carefully studied first by Harlow Shapley in 1930. He discovered roughly 70,000 stars and found it had a dense core. Then Halton Arp and William G. Melbourne continued studies in 1959. Because of the large color spread of its red giant branch (RGB) sequence, which is similar to that observed in Omega Centauri, it became the object of intense scrutiny starting in 1977 with James E. Hesser et al.
M22 is one of the nearer globular clusters to Earth at a distance of about 10,600 light-years away. It spans 32' on the sky which translates to a spatial diameter of 99 ± 9 light-years. 32 variable stars have been recorded in M22. It is projected in front of the galactic bulge and is therefore useful for its microlensing effect on the background stars in the bulge.
Despite its relative proximity to us, this metal-poor cluster's light is limited by dust extinction, giving it an apparent magnitude of 5.5 making it the brightest globular cluster visible from mid-northern latitudes (e.g. Europe and most of North America). However, due to its southerly declination, M22 never rises high in the sky and so appears less impressive to northern hemisphere observers than other summer sky globulars such as M13 and M5.
M22 is very unusual in that it is one of only four globulars (the others being M15, NGC 6441 and Palomar 6) that are known to contain a planetary nebula. It was discovered using the IRAS satellite by Fred Gillett et al.,in 1986 as a pointlike source (IRAS 18333-2357)[15] and subsequently identified as a planetary nebula in 1989 by Gillett et al.[16] The planetary nebula's central star is a blue star. The planetary nebula (designated GJJC1) is estimated to be a mere ~6,000 years old.
Two black holes of between 10 and 20 solar masses each have been discovered, initially with the Very Large Array radio telescope in New Mexico, and corroborated by the Chandra X-ray telescope, in 2012.[17] Their detection implies that gravitational ejection of black holes from clusters is not as efficient as was previously thought, and leads to estimates of a total 5 to 100 black holes within M22.[18] Interactions between stars and black holes could explain the unusually large core of the cluster.
Steve
Scopes : Explore Scientific ED102 Triplet APO - Radian Raptor Triplet APO - Orion 50mm Mount : AVX EQ |Software : KStars - EKOS - Stellar OS |Cameras : ZWO ASI533MC ASI1600MM ASI120MM-mini CPU : Mac Studio, iMac - Kstars-Ekos on Raspberry Rpi4/RPi5 |Misc : Thousand Oaks dew controller - DewNot straps - Optolong L-enhance - ZWO EAF Image Processing : PixInsight - LightRoom - Photoshop - macOS 14 - Windows 11
Nice photo Steve and thanks for the background information.
-Michael Refractors: ES AR152 f/6.5 Achromat on Twilight II, Celestron 102mm XLT f/9.8 on Celestron Heavy Duty Alt Az mount, KOWA 90mm spotting scope Binoculars: Celestron SkyMaster 15x70, Bushnell 10x50 Eyepieces: Various, GSO Superview, 9mm Plossl, Celestron 25mm Plossl Camera: ZWO ASI 120 Naked Eye: Two Eyeballs Latitude: 48.7229° N
Scopes: Explore Scientific ED102 APO, Sharpstar 61 EDPH II APO, Samyang 135 F2 (still on the Nikon).
Mount: Skywatcher HEQ5 Pro with Rowan Belt Mod
Stuff: ASI EAF Focus Motor (x2), ZWO OAG, ZWO 30 mm Guide Scope, ASI 220mm min, ASI 120mm mini, Stellarview 0.8 FR/FF, Sharpstar 0.8 FR/FF, Mele Overloock 3C.
Camera/Filters/Software: ASI 533 mc pro, ASI 120mm mini, ASI 220mm mini , IDAS LPS D-1, Optolong L-Enhance, ZWO UV/IR Cut, N.I.N.A., Green Swamp Server, PHD2, Adobe Photoshop CC, Pixinsight.
Dog and best bud: Jack
Sky: Bortle 6-7
My Astrobin: https://www.astrobin.com/users/Juno16/
Thanks for all the information about this cluster. Really nice capture with details right into the core. You are getting very nice stars on all your images. Well done.
Steve
Steve King: Light Pollution (Bortle 5)
Telescope + Mount + Guiding: W.O. Star71-ii + iOptron CEM40 EC + Orion Magnificent Mini AutoGuider
Camera: ASI 1600MM Pro + EFW Filter Wheel + Chroma 3nm Siii, Ha, Oiii + ZWO LRGB Filters
Software: PHD2; APT; PixInsight ***** My AP website: www.steveking.pictures
Jim Thommes Jim's Astrophotography
David Levy Maksutov Newtonian, Celestron Edge 9.25, FSQ-106N Refractor (on loan), WO ZenithStar 66 APO Refractor, WO Megrez II APO, Sigma 150 mm EOS Lens
Losmandy G11/Gemini, iOptron GEM45, Celestron Advanced VX, iOptron CEM70
ST8300M Camera, Atik 383L, Canon 350D (IR cut modified), ASI1600M, ASI294M, ASI260M
Observatory - Desert Astronomy Association (Shelter Valley, CA)