View source for 1806−20 cluster

{{Short description|Heavily obscured star cluster on the far side of the Milky Way}}
{{Infobox open cluster
| name = 1806−20 cluster
| epoch = J2000
| constellation = Sagittarius
| ra = {{RA|18|08|39.33}}<ref name="Aladin_cluster"/>
| dec = {{DEC|-20|24|40.0}}<ref name="Aladin_cluster"/>
| dist_ly = ~28000 ly
| dist_pc = ~8700 pc<ref name=pumpe2018>{{cite journal |bibcode=2018A&A...612A..11H |title=Extended VHE γ-ray emission towards SGR1806-20, LBV 1806-20, and stellar cluster Cl* 1806-20 |author1=H. E. S. S. Collaboration |last2=Abdalla |first2=H. |last3=Abramowski |first3=A. |last4=Aharonian |first4=F. |last5=Ait Benkhali |first5=F. |last6=Akhperjanian |first6=A. G. |last7=Angüner |first7=E. O. |last8=Arrieta |first8=M. |last9=Aubert |first9=P. |last10=Backes |first10=M. |last11=Balzer |first11=A. |last12=Barnard |first12=M. |last13=Becherini |first13=Y. |last14=Becker Tjus |first14=J. |last15=Berge |first15=D. |last16=Bernhard |first16=S. |last17=Bernlöhr |first17=K. |last18=Birsin |first18=E. |last19=Blackwell |first19=R. |last20=Böttcher |first20=M. |last21=Boisson |first21=C. |last22=Bolmont |first22=J. |last23=Bordas |first23=P. |last24=Bregeon |first24=J. |last25=Brun |first25=F. |last26=Brun |first26=P. |last27=Bryan |first27=M. |last28=Bulik |first28=T. |last29=Capasso |first29=M. |last30=Carr |first30=J. |journal=Astronomy and Astrophysics |year=2018 |volume=612 |page=612 |doi=10.1051/0004-6361/201628695 |arxiv=1606.05404 |s2cid=118345803 |display-authors=1 }}</ref>
| notes = Contains [[SGR 1806−20]] and [[LBV 1806−20]].
| names = G10.0-0.3, W31
}}
[[File:1806-20 cluster.jpg|thumb|left|H-band infrared image of 1806−20 cluster]]
'''1806−20''' (originally named the SGR 1806−20 cluster) is a heavily obscured [[star cluster]] on the far side of the [[Milky Way]], approximately 28,000 light-years distant.<ref>{{Cite journal |last1=Bibby |first1=J. |last2=Crowther |first2=P. |last3=Furness |first3=J. |last4=Clark |first4=J. |date=2008 |title=A downward revision to the distance of the 1806-20 cluster and associated magnetar from Gemini Near-Infrared Spectroscopy |journal=Monthly Notices of the Royal Astronomical Society |volume=386 |issue=1 |doi=10.1111/j.1745-3933.2008.00453.x|doi-access=free |arxiv=0802.0815 |bibcode=2008MNRAS.386L..23B |s2cid=14466990 }}</ref> Some sources claim as far as 50,000.  It contains the [[soft gamma repeater]] [[SGR 1806−20]] and the [[luminous blue variable]] [[hypergiant]] [[LBV 1806−20]], a candidate for the most luminous star in the Milky Way. [[LBV 1806−20]] and many of the other massive stars in the cluster are thought likely to end as [[supernova]]s in a few million years, leaving only [[neutron star]]s or [[black hole]]s as remnants.

The cluster is heavily obscured by intervening dust, and mostly visible in the [[infrared astronomy|infrared]]. It is part of the larger W31 [[H II region]] and [[giant molecular cloud]]. It has a compact core of ~0.2 pc in diameter with a more extended halo of ~2 pc in diameter containing the LBV<ref name=Aladin_cluster>SIMBAD/Aladin plot, of r=30 asec region around SGR B18054117-20251165</ref> and at least three [[Wolf–Rayet star]]s (of types WC8, WN6, and WN7) and an OB [[supergiant]], plus other young massive stars.<ref name=Figeretal2005>{{cite journal |arxiv=astro-ph/0501560 |doi=10.1086/429159 |title=Massive Stars in the SGR 1806-20 Cluster |year=2005 |last1=Figer |first1=Donald F. |last2=Najarro |first2=Francisco |last3=Geballe |first3=T. R. |last4=Blum |first4=R. D. |last5=Kudritzki |first5=Rolf P. |journal=The Astrophysical Journal |volume=622 |issue=1 |pages=L49–L52 |bibcode=2005ApJ...622L..49F |s2cid=14696048 }}</ref>

== See also ==
* [[Wolf–Rayet star]]
* [[LBV 1806−20]]
* [[SGR 1806−20]]
* [[Hypergiant]]
* [[Star cluster]]
* [[Luminous blue variable]]
* [[Charles Wolf (astronomer)|Charles Wolf]]
* [[Georges Rayet]]

==References==
{{Reflist}}

== External links ==
* [https://web.archive.org/web/20080706021604/http://www.aas.org/publications/baas/v33n4/aas199/850.htm ''The Unusual High-Mass Star Cluster 1806−20'' ]

{{DEFAULTSORT:Cl 1806-20}}
[[Category:Sagittarius (constellation)]]
[[Category:Open clusters]]


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