A super star cluster is a very large region that is thought to be the precursor of a globular cluster

Globular cluster

A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is...

. They typically contain a very large number of young

T Tauri star

T Tauri stars are a class of variable stars named after their prototype – T Tauri. They are found near molecular clouds and identified by their optical variability and strong chromospheric lines.-Characteristics:...

, massive stars

OB star

OB stars are hot, massive stars of spectral types O or B which form in loosely organized groups called OB associations. They are short lived, and thus don't move very far from where they were formed within their life. During their lifetime, they will emit copious amounts of ultraviolet radiation...

 that ionize a surrounding H II region

H II region

An H II region is a large, low-density cloud of partially ionized gas in which star formation has recently taken place. The short-lived, blue stars forged in these regions emit copious amounts of ultraviolet light, ionizing the surrounding gas...

, similar to our Milky Way's so-called "Ultra dense H II regions (UDHIIs)". An SSC's H II region

H II region

An H II region is a large, low-density cloud of partially ionized gas in which star formation has recently taken place. The short-lived, blue stars forged in these regions emit copious amounts of ultraviolet light, ionizing the surrounding gas...

 is in turn surrounded by a cocoon of dust

Cosmic dust

Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 µm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust .In our own Solar...

. In many cases, the stars and the H II regions will be invisible to optical observations due to high levels of extinction

Extinction (astronomy)

Extinction is a term used in astronomy to describe the absorption and scattering of electromagnetic radiation by matter between an emitting astronomical object and the observer. Interstellar extinction—also called Galactic extinction, when it occurs in the Milky Way—was first...

. As a result, the youngest SSCs are best observed in radio

Radio astronomy

Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The initial detection of radio waves from an astronomical object was made in the 1930s, when Karl Jansky observed radiation coming from the Milky Way. Subsequent observations have identified a number of...

 and infrared

Infrared astronomy

Infrared astronomy is the branch of astronomy and astrophysics that studies astronomical objects visible in infrared radiation. The wavelength of infrared light ranges from 0.75 to 300 micrometers...

.

The unique characteristics of SSCs are their large electron

Electron

The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

 densities

Density

The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

 – cm and pressure

Pressure

Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

s – K

Kelvin

The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

 cm.

While there are many examples of SSCs in other galaxies, Westerlund 1

Westerlund 1

Westerlund 1 is a compact young star cluster in the Milky Way galaxy, about 3.5–5 kpc away from Earth. In fact, it is the most massive compact young star cluster known in the entire Local Group of galaxies...

 may be the only cluster in the Milky Way

Milky Way

The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

 deserving of the title.

List

Name	Galaxy	Comments	Notes
Westerlund 1 Westerlund 1 Westerlund 1 is a compact young star cluster in the Milky Way galaxy, about 3.5–5 kpc away from Earth. In fact, it is the most massive compact young star cluster known in the entire Local Group of galaxies...  (Wd1)	Milky Way Galaxy	First SSC discovered in our galaxy.
R136	Large Magellanic Cloud Large Magellanic Cloud The Large Magellanic Cloud is a nearby irregular galaxy, and is a satellite of the Milky Way. At a distance of slightly less than 50 kiloparsecs , the LMC is the third closest galaxy to the Milky Way, with the Sagittarius Dwarf Spheroidal and Canis Major Dwarf Galaxy lying closer to the center...  (LMC)	The prototype SSC
	NGC 1569 NGC 1569 NGC 1569 is a dwarf irregular galaxy in Camelopardalis. While this faint galaxy is not a popular amateur astronomy target, it is well studied by professional astronomers, who are interested in the history of star formation within the galaxy. The galaxy is relatively nearby. Consequently, the...	Galaxy contains two SSCs

External links

• Monster Super Star Cluster Discovered In Milky Way