# 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]