query: instance_of westerlund 1
supports: Latin (Latin: ) is a classical language belonging to the Italic branch of the Indo-European languages. The Latin alphabet is derived from the Etruscan and Greek alphabets. Star clusters or star clouds are groups of stars. Two types of star 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 hundred 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 open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. 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. A super star cluster (SSC) is a very massive young open cluster that is thought to be the precursor of a globular cluster. They typically contain a very large number 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 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. A star is a luminous sphere of plasma held together by its own gravity. The nearest star 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 star 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. 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 derived from the Latin "globulus"a small sphere. A globular cluster is sometimes known more simply as a "globular". In the context of spaceflight, 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. An H II region or HII region is a region 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-ionisedH II is H in other sciencesIII 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 gas 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 gas. H II regionssometimes several hundred light-years acrossare often associated with giant molecular clouds. The Orion Nebula, now known to be an H II region, was observed in 1610 by Nicolas-Claude Fabri de Peiresc by telescope, the first such object discovered. Westerlund 1 ( 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 will probably evolve into a globular cluster . 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 J164710.2 - 455216 , 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 . Gravity, or gravitation, is a natural phenomenon by which all things with mass are brought toward (or "gravitate" toward) one another, including planets, stars and galaxies. Since energy and mass 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.
candidates: 1 cluster collection direction extinction galaxy gas giant giant molecular cloud globular cluster group hii region hundred hydrogen language latin alphabet mass matter molecular cloud moving group name natural phenomenon number object open cluster radio region result scale size sky space spaceflight sphere star stellar association super star cluster time two will
answer: open cluster