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 Bengt Westerlund in 1961 but remained largely unstudied for many years due to high interstellar absorption in its direction. In the future, it will probably evolve into a globular cluster.
| Westerlund 1 | |
|---|---|
Credit: ESO/VPHAS+ Survey/N. Wright | |
| Observation data (J2000 epoch) | |
| Right ascension | 16h 47m 04.0s |
| Declination | −45° 51′ 04.9″ |
| Distance | 3.78+0.56 −0.46 (2.6 – 4.23) kpc |
| Physical characteristics | |
| Mass | 63,000 M☉ |
| Radius | 3.26 ly |
| Estimated age | 3.50 Myr |
| Other designations | Ara Cluster, Westerlund 1, ESO 277-12, C 1644-457, VDBH 197 |
| Associations | |
| Constellation | Ara |
The cluster contains a large number of rare, evolved, high-mass stars, including: 6 yellow hypergiants, 4 red supergiants including Westerlund 1-26, one of the largest known stars, 24 Wolf-Rayet stars, a luminous blue variable, many OB supergiants, and an unusual supergiant sgB[e] star which has been proposed to be the remnant of a recent stellar merger. In addition, X-ray observations have revealed the presence of the anomalous X-ray pulsar CXO J164710.20-455217, a slow rotating neutron star that must have formed from a high-mass progenitor star. Westerlund 1 is believed to have formed in a single burst of star formation, implying the constituent stars have similar ages and compositions.
Aside from hosting some of the most massive and least-understood stars in our galaxy, Westerlund 1 is useful as a relatively nearby, easy to observe super star cluster that can help astronomers determine what occurs within extragalactic super star clusters.