View source for Astronomy:Super star cluster

{{Short description|Type of very massive young open cluster thought to be the precursor of a globular cluster}}
A '''super star cluster''' ('''SSC''') is a very massive young [[Astronomy:Open cluster|open cluster]] that is thought to be the precursor of a [[Astronomy:Globular cluster|globular cluster]].<ref name=gallagher02>{{cite journal
 | author = Gallagher
 | author2 = Grebel
 | name-list-style = amp 
 | date = 2002
 | title = Extragalactic Star Clusters: Speculations on the Future
 | journal = Extragalactic Star Clusters, IAU Symposium
 | volume = 207
 | pages = 207
 | bibcode = 2002IAUS..207..745G
|arxiv = astro-ph/0109052 }}</ref> These clusters called "super" because they are relatively more luminous and contain more mass than other young star clusters.<ref name=":0">{{Cite journal|last=Johnson|first=Kelsey|title=The Properties of Super Star Clusters In A Sample of Starburst Galaxies|year=2001|bibcode=2001PhDT.......182J|s2cid=117321058|url=https://pdfs.semanticscholar.org/998f/66fe062452fb32657a42a06c4818c2d5dd64.pdf|archive-url=https://web.archive.org/web/20170227231823/https://pdfs.semanticscholar.org/998f/66fe062452fb32657a42a06c4818c2d5dd64.pdf|url-status=dead|archive-date=2017-02-27}}</ref>  The SSC, however, does not have to physically be larger than other clusters of lower mass and luminosity.<ref name=":1">{{Cite journal|last=de Grijs|first=Richard|title="Super" Star Clusters|url=http://astro-expat.info/deGrijsJD11.pdf}}</ref>  They typically contain a very large number of young, [[Astronomy:OB star|massive stars]] that ionize a surrounding [[Astronomy:H II region|HII region]] or a so-called "Ultra dense HII region (UDHII)" in the [[Astronomy:Milky Way|Milky Way Galaxy]]<ref name="kobulnicky99">{{cite journal
 | last1 = Kobulnicky
 | first1 = Henry A.
 | last2 = Johnson
 | first2 = Kelsey E.
 | name-list-style = amp
 | date = 1999
 | title = Signatures of the Youngest Starbursts: Optically Thick Thermal Bremsstrahlung Radio Sources in Henize 2-10
 | journal = Astrophysical Journal
 | pages = 154–166
 | issue = 1
 | volume = 527
 | bibcode = 1999ApJ...527..154K
 | doi = 10.1086/308075
|arxiv = astro-ph/9907233 | s2cid = 15431678
 }}</ref> or in other galaxies (however, SSCs do not always have to be inside an HII region).  An SSC's [[Astronomy:H II region|HII region]] is in turn surrounded by a cocoon of [[Astronomy:Cosmic dust|dust]]. In many cases, the stars and the HII regions will be invisible to observations in certain wavelengths of light, such as the visible spectrum, due to high levels of [[Astronomy:Extinction|extinction]]. As a result, the youngest SSCs are best observed and photographed in [[Astronomy:Radio astronomy|radio]] and [[Astronomy:Infrared astronomy|infrared]].<ref name="johnson04">{{cite journal
 | author = Johnson
 | date = 2004
 | title = Extragalactic Ultracompact HII Regions: Probing the Birth Environments of Super Star Clusters
 | journal = ASP Conference Series
 | pages = 322
 | volume = 527
 | bibcode = 2004ASPC..322..339J
|arxiv = astro-ph/0405125 }}</ref>  SSCs, such as Westerlund 1 (Wd1), have been found in the Milky Way Galaxy.<ref>{{Cite news|url=http://www.universetoday.com/10360/super-star-cluster-discovered-in-our-own-milky-way/|title=Super Star Cluster Discovered in Our Own Milky Way - Universe Today|date=2005-03-22|access-date=2017-02-10|language=en-US|newspaper=Universe Today}}</ref> However, most have been observed in farther regions of the universe. In the galaxy [[Astronomy:Messier 82|M82]] alone, 197 young SSCs have been observed and identified using the Hubble Space Telescope.<ref>{{Cite journal|last1=Melo|first1=V. P.|last2=Muñoz-Tuñón|first2=C.|last3=Maíz-Apellániz|first3=J.|last4=Tenorio-Tagle|first4=G.|date=2005-01-01|title=Young Super Star Clusters in the Starburst of M82: The Catalog|url=http://stacks.iop.org/0004-637X/619/i=1/a=270|journal=The Astrophysical Journal|language=en|volume=619|issue=1|pages=270|doi=10.1086/426421|issn=0004-637X|arxiv = astro-ph/0409750 |bibcode = 2005ApJ...619..270M |s2cid=16452890}}</ref>

Generally, SSCs have been seen to form in the interactions between galaxies and in regions of high amounts of star formation with high enough pressures to satisfy the properties needed for the formation of a star cluster.<ref name=":0" /> These regions can include newer galaxies with much new star formation, dwarf [[Astronomy:Starburst galaxy|starburst galaxies]],<ref>{{Cite journal|last1=Hunter|first1=Deidre A.|last2=O'Connell|first2=Robert W.|title=The Star Clusters in the Starburst Irregular Galaxy NGC 1569|journal=The Astronomical Journal|year=2000|volume=20|issue=5|pages=2383–2401|doi=10.1086/316810|arxiv = astro-ph/0009280 |bibcode = 2000AJ....120.2383H |s2cid=6445978}}</ref> arms of a spiral galaxy that have a high star formation rate, and in the merging of galaxies. In an Astronomical Journal published in 1996, using pictures taken in the ultraviolet (UV) spectrum by the Hubble Space Telescope of star-forming rings in five different barred galaxies, numerous star clusters were found in clumps within the rings which had high rates of star formation. These clusters were found to have masses of about <math>10^3</math>M<sub>☉</sub>  to <math>10^5</math>M<sub>☉</sub>, ages of about 100 Myr, and radii of about 5 pc, and are thought to evolve into globular clusters later in their lifetimes.<ref>{{Cite journal|last1=Maoz|first1=D.|last2=Barth|first2=A. J.|last3=Sternberg|first3=A.|last4=Filippenko|first4=A. V.|last5=Ho|first5=L. C.|last6=Macchetto|first6=F. D.|last7=Rix|first7=H.-W.|last8=Schneider|first8=D. P.|date=1996-06-01|title=Hubble Space Telescope Ultraviolet Images of Five Circumnuclear Star-Forming Rings|journal=The Astronomical Journal|volume=111|pages=2248|doi=10.1086/117960|issn=0004-6256|arxiv = astro-ph/9604012 |bibcode = 1996AJ....111.2248M |s2cid=12241545}}</ref> These properties match those found in SSCs.

== Characteristics and properties ==
The typical characteristics and properties of SSCs:
* Mass <math>\gtrsim</math> <math>10^5</math>M<sub>☉</sub><ref name=":0" />
* Radius ≈ 5 pc ≈ <math>10^{19}</math> cm<ref name=":0" />
* Age ≈ 100 Myr<ref name=":0" /> (Although other sources state that observed SSCs have an age of 1 Gyr<ref name=":1" />)
* Large [[Physics:Electron|electron]] [[Physics:Density|densities]] <math>n_e=10^3</math>–<math>10^6</math> cm<math>^{-3}</math> (this is a property of the HII region associated with the SSC)
* [[Physics:Pressure|Pressure]]s <math>P/</math>[[Physics:Boltzmann's constant|<math>k b</math>]]<math>=10^7</math>–<math>10^{10}</math> [[Kelvin|K]] cm<math>^{-3}</math>.<ref name="johnson04" /> (this is a property of the HII region associated with the SSC)

== Hubble Space Telescope contributions ==
Given the relatively small size of SSC's compared to their host galaxies, astronomers have had trouble finding them in the past due to the limited resolution of the ground-based and space telescopes at the time. With the introduction of the [[Astronomy:Hubble Space Telescope|Hubble Space Telescope (HST)]] in the 1990s, finding SSC's (as well as other astronomical objects) became much easier thanks to the higher resolution of the HST (angular resolution of ~1/10 arcsecond<ref>{{Cite web|url=https://www.spacetelescope.org/about/faq/|title=FAQ - Frequently Asked Questions|last=|website=www.spacetelescope.org|language=en|access-date=2017-03-18}}</ref>). This has not only allowed astronomers to see SSC's, but also allowed for them to measure their properties as well as the properties of the individual stars within the SSC. Recently, a massive star, [[Astronomy:Westerlund 1-26|Westerlund 1-26]], was discovered in the SSC Westerlund 1 in the Milky Way. The radius of this star is thought to be larger than the radius of Jupiter's orbit around the Sun.<ref>{{Cite web|url=http://www.upi.com/Science_News/2017/03/10/Hubble-finds-young-super-star-cluster-giant-star/3391489160736/|title=Hubble finds young super star cluster, giant star|last=Wallace|first=Amy|date=March 10, 2017|website=UPI}}</ref> Essentially, the HST searches the night sky, specifically nearby galaxies, for star clusters and "dense stellar objects" to see if any have the properties similar to that of a SSC or an object that would, in its lifetime, evolve into a globular cluster.<ref name=":1" />

==List of SSC's==
{|class=wikitable
|- style="vertical-align:bottom;"
! Name
! Contained<br/>in Galaxy
! Comments
! Refs / Notes
! Pictures
|-
| [[Astronomy:Westerlund 1|Westerlund 1]] (Wd1)
| [[Astronomy:Milky Way|Milky Way Galaxy]]
| First SSC discovered in the [[Astronomy:Milky Way|Milky Way Galaxy]]. This SSC was discovered by Bengt Westerlund in 1961.
| <ref>{{cite journal|doi=10.1051/0004-6361:20042413|title=On the massive stellar population of the super star cluster Westerlund 1|journal=Astronomy and Astrophysics|volume=434|issue=3|pages=949|year=2005|last1=Clark|first1=J. S.|last2=Negueruela|first2=I.|last3=Crowther|first3=P. A.|last4=Goodwin|first4=S. P.|bibcode=2005A&A...434..949C|arxiv = astro-ph/0504342 |s2cid=119042919 }}</ref>
|[[File:Westerlund 1.jpg|alt=Westerlund 1|center|thumb|Westerlund 1]]
|-
| [[Astronomy:NGC 3603|NGC 3603]]
| [[Astronomy:Milky Way|Milky Way Galaxy]]
| Candidate for SSC
| <ref>{{cite journal|doi=10.1088/0004-637X/780/1/36|title=Molecular Clouds Toward the Super Star Cluster Ngc 3603; Possible Evidence for a Cloud-Cloud Collision in Triggering the Cluster Formation|journal=The Astrophysical Journal|volume=780|pages=36|year=2014|last1=Fukui|first1=Y.|last2=Ohama|first2=A.|last3=Hanaoka|first3=N.|last4=Furukawa|first4=N.|last5=Torii|first5=K.|last6=Dawson|first6=J. R.|last7=Mizuno|first7=N.|last8=Hasegawa|first8=K.|last9=Fukuda|first9=T.|last10=Soga|first10=S.|last11=Moribe|first11=N.|last12=Kuroda|first12=Y.|last13=Hayakawa|first13=T.|last14=Kawamura|first14=A.|last15=Kuwahara|first15=T.|last16=Yamamoto|first16=H.|last17=Okuda|first17=T.|last18=Onishi|first18=T.|last19=Maezawa|first19=H.|last20=Mizuno|first20=A.|issue=1|bibcode=2014ApJ...780...36F|arxiv = 1306.2090 |s2cid=53118305}}</ref>
|[[File:Stellar nursery NGC 3603.jpg|alt=\NGC 3603|center|thumb|NGC 3603]]
|-
| [[Astronomy:NGC 2070|NGC 2070]]
| [[Astronomy:Large Magellanic Cloud|Large Magellanic Cloud]] (LMC)
| Candidate for SSC
|
|[[File:The Tarantula Nebula (30 Doradus or NGC 2070).jpg|alt=\NGC 2070|center|thumb|NGC 2070]]
|-
| [[Astronomy:R136|R136]]
| [[Astronomy:Large Magellanic Cloud|Large Magellanic Cloud]] (LMC)
| The prototype SSC, inside [[Astronomy:NGC 2070|NGC 2070]]
| <ref>{{cite journal|doi=10.1086/305126|title=Star Formation in R136: A Cluster of O3 Stars Revealed by ''Hubble'' Space Telescope ''Spectroscopy''|journal=The Astrophysical Journal|volume=493|pages=180–194|year=1998|last1=Massey|first1=Philip|last2=Hunter|first2=Deidre A.|issue=1|bibcode=1998ApJ...493..180M|doi-access=free}}</ref>
|[[File:Grand star-forming region R136 in NGC 2070 (captured by the Hubble Space Telescope).jpg|alt=R136 (Located in the Tarantula Nebula)|center|thumb|R136  (Located in the Tarantula Nebula)]]
|-
| [[Astronomy:NGC 346|NGC 346]]
| [[Astronomy:Small Magellanic Cloud|Small Magellanic Cloud]] (SMC)
| May be a SSC
|[[File:Ngc346.jpg|alt=NGC 346|center|thumb|NGC 346]]
|-
| NGC 1569 A1 and A2 (NGC 1569 A)
| [[Astronomy:NGC 1569|NGC 1569]]
| Clusters A1 and A2 formed SSC A
| <ref>{{cite journal|bibcode=2000AJ....120.2383H|title=The Star Clusters in the Starburst Irregular Galaxy NGC 1569|journal=The Astronomical Journal|volume=120|issue=5|pages=2383|last1=Hunter|first1=Deidre A.|last2=O'Connell|first2=Robert W.|last3=Gallagher|first3=J. S.|last4=Smecker-Hane|first4=Tammy A.|year=2000|doi=10.1086/316810|arxiv = astro-ph/0009280 |s2cid=6445978}}</ref>
|[[File:NGC 1569.jpg|alt=NGC 1569|thumb|NGC 1569|center]]
|-
| NGC 1569 B
| [[Astronomy:NGC 1569|NGC 1569]]
| It contains older population of red giants and red supergiants
| <ref>{{cite journal|bibcode=2000AJ....120.2383H|title=The Star Clusters in the Starburst Irregular Galaxy NGC 1569|journal=The Astronomical Journal|volume=120|issue=5|pages=2383|last1=Hunter|first1=Deidre A.|last2=O'Connell|first2=Robert W.|last3=Gallagher|first3=J. S.|last4=Smecker-Hane|first4=Tammy A.|year=2000|doi=10.1086/316810|arxiv = astro-ph/0009280 |s2cid=6445978}}</ref>
|[[File:Starburst in a Dwarf Irregular Galaxy.jpg|alt=NGC 1569|thumb|NGC 1569|center]]
|-
| NGC 5253's central SSC
| [[Astronomy:NGC 5253|NGC 5253]]
| It is very dusty, and is the site of ongoing star formation. Particularly rich in [[Astronomy:O-type star|O-type stars]], containing at least 7,000. 
| 
|[[File:A Peculiar Compact Blue Dwarf Galaxy.jpg|alt=NGC 5253|thumb|NGC 5253|center]]
|}

==References==
{{Reflist}}

==External links==
*[https://www.sciencedaily.com/releases/2005/05/050528143304.htm Monster Super Star Cluster Discovered In Milky Way]

{{star}}
[[Category:Star clusters]]
[[Category:Super star clusters| ]]

{{Sourceattribution|Super star cluster}}