Template:Short description Template:Infobox globular cluster Messier 92 (also known as M92, M 92, or NGC 6341) is a globular cluster of stars in the northern constellation of Hercules.
DiscoveryEdit
It was discovered by Johann Elert Bode on December 27, 1777, then published in the Berliner Astronomisches Jahrbuch during 1779.<ref>Template:Cite book From p. 156: " […] ich am 27. Decemb. 1777 einen neuen, mir nicht bekannten Nebelfleck im Herkules, südwestlich unter dem Stern ⍳ an dessen Fusse entdeckt, der sich in einer mehrentheils runden Figur mit einem blassen Lichtschimmer zeigt." ( […] on the 27th December 1777, I discovered a new nebula, which was unknown to me, in Hercules, southwest under the star ⍳ [iota] at his feet, which appears as a mostly round shape with a pale glimmer.)</ref><ref name="kanas2007" /> It was inadvertently rediscovered by Charles Messier on March 18, 1781,Template:Efn and added as the 92nd entry in his catalogue.<ref name="garfinckle1997" /> William Herschel first resolved individual stars in 1783.
VisibilityEdit
It is one of the brighter of its sort in apparent magnitude in the northern hemisphere and in its absolute magnitude in the galaxy, but it is often overlooked by amateur astronomers due to angular proximity to bright cluster Messier 13, about 20% closer. Though when compared to M13, M92 is only slightly less bright, but about 1/3 less extended. It is visible to the naked eye under very good viewing conditions.<ref name="maa" /> With a small telescope, M92 can be seen as a nebulous smudge even in a severely light-polluted sky, and can be further resolved in darker conditions.
CharacteristicsEdit
It is also one of the galaxy's oldest clusters. It is around Template:Convert above/below the galactic plane and Template:Convert from the Galactic Center.<ref name="aj133_3_1041" /> It is about 26,700 light-years away from the Solar System.The half-light radius, or radius containing the upper half of its light emission, is 1.09 arcminutes (Template:Prime), while the tidal radius, the broadest standard measure, is 15.17Template:Prime. It appears only slightly flattened: its minor axis is about 89% ± 3% of the major.<ref name="apj721_2_1790" />
Characteristic of other globulars, it has little of the elements other than hydrogen and helium; astronomers term this low metallicity. Specifically, relative to the Sun, its iron abundance is [Fe/H] = –2.32 dex,<ref name="aj133_3_1041" /> which is 0.5% of 1.0, on this logarithmic scale, the solar abundance.<ref>Since 10−2.29 = 0.00513.</ref> This puts the estimated age range for the cluster at Template:Nowrap.<ref>Template:Cite journal</ref>
Its true diameter is 108 ly, and may have a mass corresponding to 330,000 suns.<ref name=":0">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
The cluster is not yet in, nor guaranteed to undergo, core collapse and the core radius figures as about 2 arcseconds (Template:Pprime).<ref name="aj133_3_1041" /> It is an Oosterhoff type II (OoII) globular cluster, which means it belongs to the group of metal-poor clusters with longer period RR Lyrae variable stars. The 1997 Catalogue of Variable Stars in Globular Clusters listed 28 candidate variable stars in the cluster, although only 20 have been confirmed. As of 2001, there are 17 known RR Lyrae variables in Messier 92.<ref name="aaa369_862" /> 10 X-ray sources have been detected within the 1.02 arcminute half-mass radius of the cluster, of which half are candidate cataclysmic variable stars.<ref name="apj736_2_158" /><ref>Template:Cite journal</ref>
M92 is approaching us at 112 km/sec. Its coordinates indicate that the Earth's North Celestial Pole periodically passes less than one degree of this cluster during the precession of Earth's axis. Thus, M92 was a "Polarissima Borealis", or "North Cluster", about 12,000 years ago (10,000 BC), and it will again in about 14,000 years (16,000 AD).<ref name=":0" />
The multiple stellar populations in this cluster, revealing that it hosts at least two stellar generations of stars named 1G and 2G, as well as two distinct groups of 2G stars (2GA and 2GB).<ref>Template:Cite news</ref> The helium abundances of 2GA and 2GB stars have higher mass fractions than that of the 1G stars by 0.01 and 0.04, respectively.
GalleryEdit
- M92 arp 750pix.jpg
Messier 92 - wide field view from the Isaac Newton Group of Telescopes
- M92map.png
Map showing how Messier 92 figures in the two-dimensional sky, in the east of Hercules. Maps set by convention against a southern horizon, such that east is left.
- Messier92 - SDSS DR14 (panorama).jpg
Messier 92 by the Sloan Digital Sky Survey
- Messier 92 Hubble WikiSky.jpg
Messier 92 by HST; 3.5Template:Prime view
- Globular Cluster M92 (NIRCam Image).png
Messier 92 captured by the James Webb Space Telescope’s NIRCam instrument
See alsoEdit
References and footnotesEdit
Template:Reflist Template:Notelist
External linksEdit
- Template:WikiSky
- Messier 92 @ SEDS Messier pages
- Messier 92, Galactic Globular Clusters Database page
- {{#invoke:citation/CS1|citation
|CitationClass=web }}
Template:Sky Template:Portal bar Template:Messier objects Template:Ngc65 Template:Hercules (constellation)