HD 97950, is a

multiple star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or '' galaxy'', although, broadly speaki ...

and part of a

super star cluster A super star cluster (SSC) is a very massive young open cluster that is thought to be the precursor of a globular cluster. These clusters called "super" because they are relatively more luminous and contain more mass than other young star clusters. ...

within the

NGC 3603 NGC 3603 is a nebula situated in the Carina–Sagittarius Arm of the Milky Way around 20,000 light-years away from the Solar System. It is a massive H II region containing a very compact open cluster (probably a super star cluster) HD 97950. ...

H II region. It was catalogued as a single star although it was always known to be a compact cluster. It is now resolved into a massive multiple star at the centre of one of the densest clusters in the galaxy. Only the six lettered stars A-F at the core of the cluster are typically referred to as components of HD 97950, while the remaining stars of the cluster and surrounding area are usually numbered as members of NGC 3603. The cluster itself is still called the HD 97950 cluster as well as the NGC 3603 young cluster (NGC 3603YC). There are no other notable groupings of stars in NGC 3603 and the HD 97950 cluster is often loosely referred to as simply NGC 3603.

Members

The main components are designated A1, A2, A3, B, and C, of which A1 and C are known to be spectroscopic binaries. A1a, A1b, and C are all WN6h

Wolf–Rayet star Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very high surface ...

s, amongst the most massive and luminous known. There are several dozen early O class stars (O3 and O4) in the cluster, mostly main sequence stars. There are just a handful of giants and supergiants including: one prominent early B supergiant,

Sher 25 Sher 25 is a blue supergiant star in the constellation Carina, located approximately 25,000 light years from the Sun in the H II region NGC 3603 of the Milky Way. It is a spectral type B1Iab star with an apparent magnitude of 12.2. ...

; a highly luminous O3.5 supergiant, Sher 18; and an interesting carbon-rich O9.7 supergiant, Sher 23. Over 7,500 stars have been identified in the cluster, with the least massive being smaller than the sun and the most massive over . Stars less than about have not yet reached the main sequence. Generally, only the stars with letter naming are typically referred to as components of HD 97950, more stars are listed in

. The number of WNh and early O stars exceeds any known cluster in the galaxy. The Quintuplet and Arches clusters each have around 20 young massive stars and may have masses comparable to the HD 97950 cluster, but they contain no O3 or WN6 stars at all. The rich red supergiant clusters such as

Westerlund 1 Westerlund 1 (abbreviated Wd1, sometimes called Ara Cluster) is a compact young super star cluster about 3.8 kpc (12,000 ly) away from Earth. It is thought to be the most massive young star cluster in the Milky Way, and was discovered by Ben ...

are too old to contain such stars, although may be even more massive.

R136 R136 (formerly known as RMC 136 from the Radcliffe Observatory Magellanic Clouds catalogue) is the central concentration of stars in the NGC 2070 star cluster, which lies at the centre of the Tarantula Nebula in the Large Magellanic Cloud. When ...

in the

Large Magellanic Cloud The Large Magellanic Cloud (LMC), or Nubecula Major, is a satellite galaxy of the Milky Way. At a distance of around 50 kiloparsecs (≈160,000 light-years), the LMC is the second- or third-closest galaxy to the Milky Way, after the ...

contains stars more massive than any in HD 97950, as well as large numbers of early O stars, and the cluster as a whole may be ten times as massive. It has been proposed that the star WR 42e, found 2.6 arcmin from the centre of the cluster, and J1117−6120, an O6V runaway a quarter of a degree away on the other side of the cluster, were both ejected in a 3-body interaction. Two of the stars then merged to form the extremely massive and luminous WR 42e.

Mass

The HD 97950 cluster has a total photometric mass of , and a dynamical mass of . The constituent stars have apparently dynamical segregated with the more massive stars predominantly found at the centre of the cluster. The centre of the cluster has a density of pc⁻³, ten times the

Orion Nebula The Orion Nebula (also known as Messier 42, M42, or NGC 1976) is a diffuse nebula situated in the Milky Way, being south of Orion's Belt in the constellation of Orion. It is one of the brightest nebulae and is visible to the naked eye in the nig ...

and comparable to R136.

Age

Fitting the main sequence, and pre-main sequence gives a cluster age of 1 million years or less. There is no clear

main sequence turnoff The turnoff point for a star refers to the point on the Hertzsprung-Russell diagram where it leaves the main sequence after its main fuel is exhaustedthe main sequence turnoff. By plotting the turnoff points of individual stars in a star cluster ...

, although the most massive stars are modelled best with an age of 2.5 million years, but are compatible with an age around one million years. A small number of stars, for example Sher 25, apparently show much greater ages and it has been suggested that there is either ongoing star formation, or an earlier burst of star formation. Other studies have estimated ages up to 2 million years, but the existence of the most massive and luminous stars provide a hard upper limit of 2.5 million years on the possible age. This is one of the youngest clusters in the galaxy. The Arches Cluster is around 2.5 million years old, the Quintuplet cluster nearly double that, and the various red supergiant clusters obviously even older. Even R136 is thought to be near to 2 million years old.

Trumpler 14 Trumpler 14 (''Tr 14'') is an open cluster with a diameter of , located within the inner regions of the Carina Nebula, approximately from Earth. Together with the nearby Trumpler 16, they are the main clusters of the Carina OB1 stellar associat ...

in the

Carina Nebula The Carina Nebula or Eta Carinae Nebula (catalogued as NGC 3372; also known as the Great Carina Nebula) is a large, complex area of bright and dark nebulosity in the constellation Carina, located in the Carina–Sagittarius Arm of the Milky Wa ...

is thought to be as little as 300,000 - 500,000 years old, but is much less massive.

Members

Mass

Age

References

Further reading