Messier 92 Explained

Messier 92
Epoch:J2000
Class:IV
Constellation:Hercules
Dist Ly:26.7abbr=onNaNabbr=on
Appmag V:6.4[1]
Size V:14' arc minutes
Metal Fe:–2.32
Names:M92, NGC 6341, GCl 59

Messier 92 (also known as M92, M 92, or NGC 6341) is a globular cluster of stars in the northern constellation of Hercules.

Discovery

It was discovered by Johann Elert Bode on December 27, 1777, then published in the Berliner Astronomisches Jahrbuch during 1779.[2] It was inadvertently rediscovered by Charles Messier on March 18, 1781, and added as the 92nd entry in his catalogue. William Herschel first resolved individual stars in 1783.

Visibility

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. 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.

Characteristics

It is also one of the galaxy's oldest clusters. It is around 16abbr=onNaNabbr=on above/below the galactic plane and 33abbr=onNaNabbr=on from the Galactic Center. 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, while the tidal radius, the broadest standard measure, is 15.17. It appears only slightly flattened: its minor axis is about 89% ± 3% of the major.

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, which is 0.5% of 1.0, on this logarithmic scale, the solar abundance.[3] This puts the estimated age range for the cluster at .[4]

Its true diameter is 109 ly, and may have a mass corresponding to 330,000 suns.[5]

The cluster is not yet in, nor guaranteed to undergo, core collapse and the core radius figures as about 2 arcseconds . 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. 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.[6]

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).

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).[7] 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.

See also

External links

Notes and References

  1. Web site: Messier 92 . 30 April 2022 . SEDS Messier Catalog.
  2. Book: Bode . Astronomisches Jahrbuch oder Ephemeriden für das Jahr 1782. . Astronomical Yearbook or Ephemerides for the Year 1782. . 1779 . George Jacob Decker . Berlin, (Germany) . 156 . German . Zweyter Theil 20. Beobachtung des Kometen von 1779 und Entdeckung einiger neuen Nebelsterne [Second Part. 20. Observation of the comet of 1779 and discovery of some new nebulae]. 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.)
  3. Since 10−2.29 = 0.00513.
  4. Di Cecco. A.. Becucci. R.. Bono. G.. Monelli. M.. Stetson. P. B.. Degl'Innocenti. S.. Moroni. P. G. Prada. Nonino. M.. Weiss. A.. Buonanno. R.. Calamida. A.. 2010-06-27. On the absolute age of the Globular Cluster M92. Publications of the Astronomical Society of the Pacific. 122. 895. 991–999. en. 10.1086/656017. 1006.5217. 2010PASP..122..991D . free.
  5. Web site: Messier Object 92 . 2022-05-28 . www.messier.seds.org.
  6. Ferraro . F. R. . Paltrinieri . B. . Fusi Pecci . F. . Rood . R. T. . Dorman . B. . 1998-01-01 . Faint UV Objects in the Core of Ggcs: a New Subclass of Cvs? . Ultraviolet Astrophysics Beyond the IUE Final Archive . 413 . 561. 1998ESASP.413..561F .
  7. News: World . FTT . Astronomers discover new insights into multiple stellar populations in Messier 92 using James Webb .