Messier 28

Messier 28
Globular cluster Messier 28 in Sagittarius
Observation data (J2000 epoch)
Class	IV [1]
Constellation	Sagittarius
Right ascension	18h 24m 32.89s [2]
Declination	–24° 52′ 11.4″ [2]
Distance	18.26 ± 0.98  kly (5.6 ± 0.3  kpc) [3]
Apparent magnitude (V)	6.8 [4]
Apparent dimensions (V)	11′.2 [5]
Physical characteristics
Mass	5.51×105 [6]   M☉
Radius	30 ly [7]
VHB	15.55 ± 0.10 [8]
Metallicity	${\displaystyle {\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}}$ = –1.32 [6] dex
Estimated age	12.0  Gyr [9]
Notable features	Contains first pulsar discovered in a globular [10]
Other designations	GCl 94, M 28, NGC 6626 [2]
See also: Globular cluster, List of globular clusters

Messier 28 or M28, also known as NGC 6626, is a globular cluster of stars in the center-west of Sagittarius. It was discovered by French astronomer Charles Messier in 1764. ^{[11] [lower-alpha 1]} He briefly described it as a "nebula containing no star... round, seen with difficulty in 31⁄2-foot telescope; Diam 2′." ^[12]

In the sky it is less than a degree to the northwest of the 3rd magnitude star Kaus Borealis (Lambda Sgr). This cluster is faintly visible as a hazy patch with a pair of binoculars ^[11] and can be readily found in a small telescope with an 8 cm (3.1 in) aperture, showing as a nebulous feature spanning 11.2  arcminutes. Using an aperture of 15 cm (5.9 in), the core becomes visible and a few distinct stars can be resolved, along the periphery. Larger telescopes will provide greater resolution, ^[5] one of 25 cm (9.8 in) revealing a dense 2′ core, with more density within. ^[11]

It is about 18,300 light-years away from Earth. ^[3] It is about 551000  M_☉ ^[6] and its metallicity (averaging −1.32 which means more than 10 times less than our own star), coherency and preponderence of older stellar evolution objects, support its dating to very roughly 12 billion years old. ^[9] 18 RR Lyrae type variable stars have been found within.

It bore the first discovery of a millisecond pulsar in a globular cluster – PSR B1821–24. This was using the Lovell Telescope at Jodrell Bank Observatory, England. ^[10] A total of 11 further of these have since been detected in it with the telescope at Green Bank Observatory, West Virginia. As of 2011, these number the third-most in a cluster tied to the Milky Way, following Terzan 5 and 47 Tucanae. ^[13]

Gallery

• 
  Messier 28 taken by Hubble. ^[14]
• 
  2.5' view of M28 taken by Hubble Space Telescope.
• 
  Messier 28 on 2MASS; wide angle
• 
  Map showing location of M28

See also

• List of Messier objects

References and footnotes

References

1. Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin, 849 (849): 11–14, Bibcode:1927BHarO.849...11S.
2. "M 28". SIMBAD . Centre de données astronomiques de Strasbourg . Retrieved 2006-11-16.
3. Oliveira, R. A. P.; Ortolani, S.; Barbuy, B.; Kerber, L. O.; Maia, F. F. S.; Bica, E.; Cassisi, S.; Souza, S. O.; Pérez-Villegas, A. (2022). "Precise distances from OGLE-IV member RR Lyrae stars in six bulge globular clusters". Astronomy & Astrophysics. 657: A123. arXiv: 2110.13943 . Bibcode:2022A&A...657A.123O. doi:10.1051/0004-6361/202141596. S2CID   239998638.
4. "Messier 28". SEDS Messier Catalog. Retrieved 28 April 2022.
5. Inglis, Mike (2004), Astronomy of the Milky Way: Observer's guide to the northern sky, Patrick Moore's Practical Astronomy Series, vol. 1, Springer, p. 21, Bibcode:2003amwn.book.....I, ISBN   978-1852337094.
6. Boyles, J.; et al. (November 2011), "Young Radio Pulsars in Galactic Globular Clusters", The Astrophysical Journal, 742 (1): 51, arXiv: 1108.4402 , Bibcode:2011ApJ...742...51B, doi:10.1088/0004-637X/742/1/51, S2CID   118649860.
7. From trigonometry: radius = distance × sin( diameter_angle / 2 ) = 30 ly
8. Testa, Vincenzo; et al. (February 2001), "Horizontal-Branch Morphology and Dense Environments: Hubble Space Telescope Observations of Globular Clusters NGC 2298, 5897, 6535, and 6626", The Astronomical Journal, 121 (2): 916–934, Bibcode:2001AJ....121..916T, doi: 10.1086/318752
9. Koleva, M.; et al. (April 2008), "Spectroscopic ages and metallicities of stellar populations: validation of full spectrum fitting", Monthly Notices of the Royal Astronomical Society , 385 (4): 1998–2010, arXiv: 0801.0871 , Bibcode:2008MNRAS.385.1998K, doi:10.1111/j.1365-2966.2008.12908.x, S2CID   17571531
10. "JBO - Stars". Jodrell Bank Observatory . Retrieved 2007-06-01.
11. Thompson, Robert Bruce; Thompson, Barbara Fritchman (2007), Illustrated Guide to Astronomical Wonders, Diy Science, O'Reilly Media, Inc., p. 402, ISBN   978-0596526856.
12. Burnham, Robert (1979), Burnham's celestial handbook: an observer's guide to the universe beyond the solar system, Dover books explaining science, vol. 3 (2nd ed.), Dover Publications, p.  1609, ISBN   978-0486236735
13. Bogdanov, Slavko; et al. (April 2011), "Chandra X-ray Observations of 12 Millisecond Pulsars in the Globular Cluster M28", The Astrophysical Journal, 730 (2): 81, arXiv: 1101.4944 , Bibcode:2011ApJ...730...81B, doi:10.1088/0004-637X/730/2/81, S2CID   118621389
14. "Nebulous, but no nebula". www.spacetelescope.org. Retrieved 11 March 2019.

Footnotes

1. On July 27

External links

• Globular Cluster M28 @ SEDS Messier pages
• Messier 28, Galactic Globular Clusters Database page
• Messier 28 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images