instance_of westerlund 1
Westerlund ___MASK59___ ( also called Ara Cluster , designated Wd1 ) is a compact young super star cluster in the Milky Way galaxy , about 3 . 5 -- 5 kpc away from Earth . It is one of the most massive young star clusters 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 ___MASK18___ probably evolve into a globular cluster . The cluster contains a large number of rare , evolved , high - ___MASK14___ stars , including : 6 yellow hypergiants , 4 red supergiants including Westerlund ___MASK59___ - 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 . 2 - 455216 , a slow rotating neutron star that must have formed from a high - ___MASK14___ progenitor star . Westerlund ___MASK59___ 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 ___MASK59___ is useful as a relatively nearby , easy to observe super star cluster that can help astronomers determine what occurs within extragalactic super star clusters . A ___MASK20___ is a luminous ___MASK44___ of plasma held together by its own gravity . The nearest ___MASK20___ to Earth is the Sun . Many other stars are visible to the naked eye from Earth during the night , appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth . Historically , the most prominent stars were grouped into constellations and asterisms , the brightest of which gained proper names . Astronomers have assembled ___MASK20___ catalogues that identify the known stars and provide standardized stellar designations . However , most of the stars in the Universe , including all stars outside our galaxy , the Milky Way , are invisible to the naked eye from Earth . Indeed , most are invisible from Earth even through the most powerful telescopes . An H II ___MASK75___ or ___MASK92___ is a ___MASK75___ of interstellar atomic hydrogen that is ionized . ( H is the chemical symbol for hydrogen , and " II " is the Roman numeral for 2 . It is customary in astronomy to use the Roman numeral I for neutral atoms , II for singly - ionised  H II is H in other sciences  III for doubly - ionised , e . g . O III is O , etc . H II , or H , consists of free protons .) It is typically a cloud of partially ionized ___MASK58___ in which star formation has recently taken place , with a size ranging from one to hundreds of light years , and density from a few to about a million particles per cubic cm . The short - lived blue stars created in these regions emit copious amounts of ultraviolet light that ionize the surrounding ___MASK58___ . H II regions  sometimes several hundred light - years across  are often associated with giant molecular clouds . The Orion Nebula , now known to be an H II ___MASK75___ , was observed in 1610 by Nicolas - Claude Fabri de Peiresc by telescope , the first such object discovered . A super ___MASK20___ ___MASK10___ ( SSC ) is a very massive young ___MASK71___ that is thought to be the precursor of a ___MASK8___ . They typically contain a very large ___MASK16___ of young , massive stars that ionize a surrounding H II region , similar to the Milky Way Galaxy ' s so - called " Ultra dense H II regions ( UDHIIs )". 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 ___MASK18___ be invisible to optical observations due to high levels of extinction . As a ___MASK38___ , the youngest SSCs are best observed in radio and infrared . A ___MASK8___ 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 ___MASK21___ of star cluster is derived from the Latin " globulus " a small ___MASK44___ . A ___MASK8___ is sometimes known more simply as a " globular ". Gravity , or gravitation , is a natural ___MASK80___ by which all things with ___MASK14___ are brought toward ( or " gravitate " toward ) one another , including planets , stars and galaxies . Since energy and ___MASK14___ are equivalent , all forms of energy , including light , also cause gravitation and are under the influence of it . On Earth , gravity gives weight to physical objects and causes the ocean tides . The gravitational attraction of the original gaseous matter present in the Universe caused it to begin coalescing , forming stars  and the stars to group together into galaxies  so gravity is responsible for many of the large scale structures in the Universe . Gravity has an infinite range , although its effects become increasingly weaker on farther objects . ___MASK20___ clusters or ___MASK20___ clouds are groups of stars . ___MASK73___ types of ___MASK20___ clusters can be distinguished : globular clusters are tight groups of hundreds or thousands of very old stars which are gravitationally bound , while open clusters , more loosely clustered groups of stars , generally contain fewer than a few ___MASK24___ members , and are often very young . Open clusters become disrupted over time by the gravitational influence of giant molecular clouds as they move through the galaxy , but cluster members will continue to move in broadly the same direction through space even though they are no longer gravitationally bound ; they are then known as a stellar association , sometimes also referred to as a " moving group ". An ___MASK71___ is a ___MASK74___ of up to a few thousand stars that were formed from the same ___MASK45___ ___MASK60___ and have roughly the same ___MASK47___ . More than 1 , 100 open clusters have been discovered within the Milky Way Galaxy , and many more are thought to exist . They are loosely bound by mutual gravitational attraction and become disrupted by close encounters with other clusters and clouds of gas as they orbit the galactic center . This can result in a migration to the main body of the galaxy and a loss of cluster members through internal close encounters . Open clusters generally survive for a few hundred million years , with the most massive ones surviving for a few billion years . In contrast , the more massive globular clusters of stars exert a stronger gravitational attraction on their members , and can survive for longer . Open clusters have been found only in spiral and irregular galaxies , in which active star formation is occurring . In the context of ___MASK26___ , a satellite is an artificial object which has been intentionally placed into orbit . Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as Earth ' s Moon . Latin ( Latin : ) is a classical ___MASK7___ belonging to the Italic ___MASK15___ of the Indo - European languages . The ___MASK70___ is derived from the Etruscan and Greek alphabets .