# Westerhout 49
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{{More footnotes|date=March 2009}}
{{short description|Strong radio source in the constellation of Sagittarius}}
{{Infobox nebula
| name = Westerhout 49
| image = W49 UKIDSS JHK.tiff
| caption = UKIDSS JHK image of W49
| type = H II region
| constellation = [Aquila](/source/Aquila_(constellation))
| epoch = [J2000.0](/source/J2000.0)
| ra = {{RA|19|10|17}}
| dec = {{DEC|+09|06|00}}
| size_v =
| radius_ly =
| absmag_v =
| appmag_v =
| dist_ly =
| notes =
| names = W49, Westerhout 49
}}
In astronomy '''Westerhout 49''' also known as '''W49''', is a strong galactic thermal radio source characteristic of an [HII region](/source/HII_region). It was discovered by [Gart Westerhout](/source/Gart_Westerhout) in 1958.
Its distance is estimated to be about 11.1 kpcs or 36,000 light years.[{{Cite web|title = Uncloaking the King of the Milky Way: The largest star in our home galaxy's largest stellar nursery|url = http://www.nanowerk.com/news2/space/newsid=37116.php|website = www.nanowerk.com|access-date = 2016-01-12}}] and it lies in the galactic plane about the same distance from the [Galactic Center](/source/Galactic_Center) as does the Sun. It has been compared to the giant HII region [NGC 3603](/source/NGC_3603) which is about half as distant. Non-thermal radiation has been found which is believed to be from an old [supernova](/source/supernova) remnant. Gaseous molecular outflows have been detected as well as H2O (water) [masers](/source/masers) . No optical counterpart has yet been discovered. While this is partly due to interstellar absorption, any tight clustering of stars at such a great distance in the galactic plane would be scarcely distinguishable from the general background.{{citation needed|date=February 2013}}
A study published in 2014, where the [VLT](/source/Very_Large_Telescope) has been used among other instruments, shows the presence of a very massive star in the central cluster of this star-forming region. The parameters of said star (''W49nr1, also known as [WBB2016] 1''[{{Cite journal|last1=Wu|first1=Shi-Wei|last2=Bik|first2=Arjan|last3=Bestenlehner|first3=Joachim M.|last4=Henning|first4=Thomas|last5=Pasquali|first5=Anna|last6=Brandner|first6=Wolfgang|last7=Stolte|first7=Andrea|date=2016-05-01|title=The massive stellar population of W49: A spectroscopic survey|journal=Astronomy and Astrophysics|volume=589|pages=A16|doi=10.1051/0004-6361/201527823|arxiv=1602.05190 |bibcode=2016A&A...589A..16W |issn=0004-6361|doi-access=free}}]) are so far poorly constrained, but a luminosity of several million times that of the Sun is estimated as well as an initial mass between 100 and 180 [solar mass](/source/solar_mass)es, and perhaps even more, what would place it among both the [most luminous](/source/Most_luminous_stars) and [massive](/source/List_of_most_massive_stars) stars known.[{{cite journal|bibcode=2014A&A...568L..13W|title=The discovery of a very massive star in W49|journal=Astronomy & Astrophysics|volume=568|last1=Wu|first1=S. W.|last2=Bik|first2=A|last3=Henning|first3=T. H.|last4=Pasquali|first4=A.|last5=Brandner|first5=W.|last6=Stolte|first6=A.|year=2014|pages=L13 |doi=10.1051/0004-6361/201424154|arxiv = 1407.4804 |s2cid=55277847 }}] Another star located in the region, [[WBB2016 2|[WBB2016] 2]], has a mass of 250 solar masses, and is also one of the most luminous and massive stars known.[{{Cite journal|last1=Wu|first1=Shi-Wei|last2=Bik|first2=Arjan|last3=Bestenlehner|first3=Joachim M.|last4=Henning|first4=Thomas|last5=Pasquali|first5=Anna|last6=Brandner|first6=Wolfgang|last7=Stolte|first7=Andrea|date=2016-05-01|title=The massive stellar population of W49: A spectroscopic survey|journal=Astronomy and Astrophysics|volume=589|pages=A16|doi=10.1051/0004-6361/201527823|arxiv=1602.05190 |bibcode=2016A&A...589A..16W |issn=0004-6361|doi-access=free}}]
==See also==
* [W49B](/source/W49B)
* [List of most massive stars](/source/List_of_most_massive_stars)
==References==
{{reflist}}
*A Survey of the Continuous Radiation from the Galactic System at a Frequency of 1390 Mc/s, G. Westerhout, Bull. Astron. Inst. Neth.'''14''', 215, 1958.
*A Distant HII Region in the Galaxy, K. Akabane and F. J. Kerr ([Frank John Kerr](/source/Frank_John_Kerr)), Aust. J. Phys. '''18''', 91, 1965.
*Galactic HII Regions. The nature of the Radio Source W49, P. G. Mezger and J. Schraml, Astropys. J.'''150''', 807,1967.
*High Resolution Observations of the Radio Source W49, C. G. Wynn-Williams, Mon. Not. R. astr. Soc. '''142''', 453 1969.
*High Resolution Far-infrared Observations of HII Regions: Sagittarius B2, W49, DR 21- W75, P. M. Harvey, M. F. Campbell and W. F. Hoffman, Astrophys. J. '''211''', 786, 1977.
==External links==
* {{commons category-inline}}
{{Aquila (constellation)|state=collapsed}}
Category:H II regions
Category:Aquila (constellation)
{{nebula-stub}}
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Adapted from the Wikipedia article [Westerhout 49](https://en.wikipedia.org/wiki/Westerhout_49) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Westerhout_49?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.