Super star cluster

A super star cluster (SSC) is a very large region that is thought to be the precursor of a globular cluster.[1] They typically contain a very large number of young, massive stars that ionize a surrounding H II region, similar to our Milky Way's so-called "Ultra dense H II regions (UDHIIs)".[2] An SSC's H II region is in turn surrounded by a cocoon of dust. In many cases, the stars and the H II regions will be invisible to optical observations due to high levels of extinction. As a result, the youngest SSCs are best observed in radio and infrared.[3]

The unique characteristics of SSCs are their large electron densities $n_e=10^3$$10^6$ cm$^{-3}$ and pressures $P/$$k_b$$=10^7$$10^{10}$ K cm$^{-3}$.[3]

While there are many examples of SSCs in other galaxies, Westerlund 1 may be the only cluster in the Milky Way deserving of the title.[4]

List

Westerlund 1 (Wd1) Milky Way Galaxy First SSC discovered in our galaxy. [5]
R136 Large Magellanic Cloud (LMC) The prototype SSC [6]
NGC 1569 Galaxy contains two SSCs [7]

References

1. ^ Gallagher & Grebel (2002). "Extragalactic Star Clusters: Speculations on the Future". Extragalactic Star Clusters, IAU Symposium: 207. arXiv:astro-ph/0109052. Bibcode:2002IAUS..207..745G.
2. ^ Kobulnicky & Johnson; Johnson, Kelsey E. (1999). "Signatures of the Youngest Starbursts: Optically Thick Thermal Bremsstrahlung Radio Sources in Henize 2-10". ApJ 527 (1): 154–166. arXiv:astro-ph/9907233. Bibcode:1999ApJ...527..154K. doi:10.1086/308075.
3. ^ a b Johnson (2004). "Extragalactic Ultracompact HII Regions: Probing the Birth Environments of Super Star Clusters". Astronomical Society of the Pacific Conference Series 527: 322. arXiv:astro-ph/0405125. Bibcode:2004ASPC..322..339J.
4. ^ "Young and Exotic Stellar Zoo: ESO's Telescopes Uncover Super Star Cluster in the Milky Way". ESO. March 22, 2005. Retrieved 2007-03-20.
5. ^ Astronomy and Astrophysics, "On the massive stellar population of the super star cluster Westerlund 1", Clark, J. S.; Negueruela, I.; Crowther, P. A.; Goodwin, S. P., Volume 434, Issue 3, May II 2005, pp.949-969, doi:10.1051/0004-6361:20042413 , Bibcode2005A&A...434..949C , arXiv:astro-ph/0504342v2
6. ^ Astrophysical Journal, "Star Formation in R136: A Cluster of O3 Stars Revealed by Hubble Space Telescope Spectroscopy", Massey, Philip; Hunter, Deidre A., 01/1998, v.493, p.180, doi:10.1086/305126 , Bibcode1998ApJ...493..180M
7. ^ "The Star Clusters in the Starburst Irregular Galaxy NGC 1569" http://adsabs.harvard.edu/abs/2000AJ....120.2383H