Editing Betelgeuse (section)

==== Supersonic bow shock ====
Betelgeuse is travelling through the interstellar medium at a speed of {{val|30|u=km/second}} (i.e. ~{{val|6.3|u=AU/year}}) creating a [[Bow shocks in astrophysics|bow shock]].<ref name=MOHAMED1/><ref name=LAMERS1999>
{{cite book
 | last1=Lamers |first1=Henny J.G.L.M.
 | last2=Cassinelli |first2=Joseph P.
 | name-list-style=amp
 | date=June 1999
 | title=Introduction to Stellar Winds
 | publisher=Cambridge University Press
 | location=Cambridge, UK
 | isbn=978-0-521-59565-0
 | bibcode=1999isw..book.....L
}}
</ref>
The shock is not created by the star, but by its powerful [[stellar wind]] as it ejects vast amounts of gas into the interstellar medium at a speed of {{val|17|u=km/s}}, heating the material surrounding the star, thereby making it visible in infrared light.<ref name=ESA3>
{{cite press release
 |title=Akari Infrared Space Telescope: Latest science highlights
 |publisher=[[European Space Agency]]
 |url=http://www.esa.int/Our_Activities/Space_Science/Akari_infrared_space_telescope_latest_science_highlights
 |date=19 November 2008
 |access-date=25 June 2012
 |archive-url=https://web.archive.org/web/20110217144724/http://www.esa.int/esaSC/SEMCJT4DHNF_index_1.html
 |archive-date= 17 February 2011}}</ref> Because Betelgeuse is so bright, it was only in 1997 that the bow shock was first imaged. The [[comet]]ary structure is estimated to be at least one parsec wide, assuming a distance of 643&nbsp;light-years.<ref name=NORIEGA1>
{{cite journal
 | last1=Noriega-Crespo | first1=Alberto   | last2=van Buren | first2=Dave
 | last3=Cao        | first3=Yu            | last4=Dgani     | first4=Ruth
 | year=1997
 | title=A parsec-size bow shock around Betelgeuse
 | journal=[[Astronomical Journal]]
 | volume=114  | pages=837–40
 | bibcode=1997AJ....114..837N
 | doi=10.1086/118517  | doi-access=free
}}
</ref>{{efn|
"Noriega in 1997 estimated the size to be 0.8&nbsp;parsecs, having assumed the earlier distance estimate of 400 ly. With a current distance estimate of 643&nbsp;ly, the bow shock would measure ~1.28 parsecs or over 4&nbsp;ly."<ref name=NORIEGA1/>
}}

[[Fluid dynamics|Hydrodynamic]] simulations of the bow shock made in 2012 indicate that it is very young—less than 30,000&nbsp;years old—suggesting two possibilities: That Betelgeuse moved into a region of the interstellar medium with different properties only recently or that Betelgeuse has undergone a significant transformation producing a changed stellar wind.<ref name=ASTROBITES1>
{{cite web
 |last=Newton |first=Elizabeth
 |date=26 April 2012
 |title=This star lives in exciting times, or, how did Betelgeuse make that funny shape?
 |website=Astrobites (astrobites.com)
 |url=http://astrobites.com/2012/04/26/this-star-lives-in-exciting-times-or-how-did-betelgeuse-make-that-funny-shape/
 |access-date=25 June 2012  |url-status=dead
 |archive-url=https://web.archive.org/web/20120430035007/http://astrobites.com/2012/04/26/this-star-lives-in-exciting-times-or-how-did-betelgeuse-make-that-funny-shape/
 |archive-date=30 April 2012
}}
</ref>
A 2012 paper, proposed that this phenomenon was caused by Betelgeuse transitioning from a [[blue supergiant]] (BSG) to a red supergiant (RSG). There is evidence that in the late evolutionary stage of a star like Betelgeuse, such stars "may undergo rapid transitions from red to blue and vice versa on the Hertzsprung–Russell diagram, with accompanying rapid changes to their stellar winds and bow shocks."<ref name="MOHAMED1">{{cite journal
 | last1=Mohamed |first1=S.
 | last2=Mackey |first2=J.
 | last3=Langer |first3=N.
 | year=2012
 | title=3D simulations of Betelgeuse's bow shock
 | journal=[[Astronomy & Astrophysics]]
 | volume= 541  | page=A1
 | bibcode=2012A&A...541A...1M
 | doi=10.1051/0004-6361/201118002
 | arxiv=1109.1555  | s2cid=118435586
}}
</ref><ref name=MACKEY1>
{{cite journal
 | last1=MacKey  | first1=Jonathan     | last2=Mohamed | first2=Shazrene
 | last3=Neilson | first3=Hilding R.   | last4=Langer  | first4=Norbert
 | last5=Meyer   | first5=Dominique M.-A.
 | year=2012
 | title=Double bow shocks around young, runaway red supergiants: Application to Betelgeuse
 | journal=The Astrophysical Journal
 | volume=751  | issue=1  | page=L10
 | bibcode=2012ApJ...751L..10M
 | doi=10.1088/2041-8205/751/1/L10
 | arxiv = 1204.3925  | s2cid=118433862
}}</ref> Moreover, if future research bears out this hypothesis, Betelgeuse may prove to have traveled close to 200,000 AU as a red supergiant scattering as much as {{val|3|u=M_solar}} along its trajectory.