View source for WR 104

{{short description|Triple star system}}
{{Use mdy dates|date=June 2013}}
{{Starbox begin
| name=WR 104
}}
{{Starbox image
| image=[[File:Wr104 sslkeck big.jpg|280px]]
| caption=WR 104
}}
{{Starbox observe
| epoch=J2000
| ra={{RA|18|02|04.07}}<ref name=2mass>{{cite journal |bibcode=2003yCat.2246....0C |title=VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003) |journal=CDS/ADC Collection of Electronic Catalogues |pages=II/246 |volume=2246 |last1=Cutri |first1=Roc M. |last2=Skrutskie |first2=Michael F. |last3=Van Dyk |first3=Schuyler D. |last4=Beichman |first4=Charles A. |last5=Carpenter |first5=John M. |last6=Chester |first6=Thomas |last7=Cambresy |first7=Laurent |last8=Evans |first8=Tracey E. |last9=Fowler |first9=John W. |last10=Gizis |first10=John E. |last11=Howard |first11=Elizabeth V. |last12=Huchra |first12=John P. |last13=Jarrett |first13=Thomas H. |last14=Kopan |first14=Eugene L. |last15=Kirkpatrick |first15=J. Davy |last16=Light |first16=Robert M. |last17=Marsh |first17=Kenneth A. |last18=McCallon |first18=Howard L. |last19=Schneider |first19=Stephen E. |last20=Stiening |first20=Rae |last21=Sykes |first21=Matthew J. |last22=Weinberg |first22=Martin D. |last23=Wheaton |first23=William A. |last24=Wheelock |first24=Sherry L. |last25=Zacarias |first25=N. |year=2003 |url=http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=II/246 |access-date=November 16, 2021 |archive-date=April 21, 2021 |archive-url=https://web.archive.org/web/20210421020651/https://vizier.u-strasbg.fr/viz-bin/VizieR?-source=II%2F246 |url-status=live }}</ref>
| dec={{DEC|-23|37|41.2}}<ref name=2mass/>
| appmag_v=13.28 (12.7 - 14.6)<ref name=williams2014>{{cite journal|last1=Williams|first1=P. M.|title=Eclipses and dust formation by WC9 type Wolf–Rayet stars|journal=Monthly Notices of the Royal Astronomical Society|volume=445|issue=2|year=2014|pages=1253–1260|issn=0035-8711|doi=10.1093/mnras/stu1779|doi-access=free |bibcode=2014MNRAS.445.1253W|arxiv = 1408.6759 |s2cid=119264818}}</ref> + 15.36<ref name=wallace/>
| constell= [[Sagittarius (constellation)|Sagittarius]]
}}
{{Starbox character
| type=[[Wolf–Rayet star]]
| class= WC9d/B0.5V<ref name=hucht>{{Cite journal | doi = 10.1016/S1387-6473(00)00112-3| title = The VIIth catalogue of galactic Wolf–Rayet stars| year = 2001| last1 = Van Der Hucht | first1 = K. A. | journal = New Astronomy Reviews| volume = 45| issue = 3| pages = 135–232| bibcode = 2001NewAR..45..135V}}</ref> + O8V–O5V<ref name=soulain/>
}}
{{Starbox astrometry
| radial_v=
| prop_mo_ra=0.161<ref name=dr2/>
| prop_mo_dec=−1.827<ref name=dr2/>
| parallax=0.2431
| p_error=0.0988
| parallax_footnote=<ref name=dr2>{{cite DR2|4069167258796371712}}</ref>
| absmag_v={{nowrap|−5.4 (−4.8 + −4.6)<ref name="Williamsvan der Hucht2000">{{cite journal|last1=Williams|first1=P. M.|last2=van der Hucht|first2=K. A.|title=Spectroscopy of WC9 Wolf–Rayet stars: a search for companions|journal=Monthly Notices of the Royal Astronomical Society|volume=314|issue=1|year=2000|pages=23–32|issn=0035-8711|doi=10.1046/j.1365-8711.2000.03332.x|bibcode=2000MNRAS.314...23W|doi-access=free}}</ref>}}
| dist_pc={{val|2,580|120|fmt=commas}}<ref name=soulain/>
}}
{{Starbox orbit
| reference=<ref name=lamberts>{{cite journal|bibcode=2012A&A...546A..60L|arxiv=1202.2060|title=Impact of orbital motion on the structure and stability of adiabatic shocks in colliding wind binaries|journal=Astronomy & Astrophysics|volume=546|pages=A60|last1=Lamberts|first1=A.|last2=Dubus|first2=G.|last3=Lesur|first3=G.|last4=Fromang|first4=S.|year=2012|doi=10.1051/0004-6361/201219006|s2cid=119202656}}</ref>
| period_unitless = 241.5 days
| eccentricity = < 0.06
| inclination = < 16
| axis_unitless = 2.34 [[astronomical unit|AU]]
}}
{{Starbox detail
| mass = 30<ref name=soulain/>
| luminosity = 120,000<ref name=soulain/>
| age_myr = 7<ref name=soulain/>
}}
{{Starbox detail|no_heading=y
| component1 = WR
| mass =  10<ref name=soulain>{{cite journal|arxiv=1806.08525|last1=Soulain|first1=A|title=The SPHERE view of Wolf–Rayet 104|last2=Millour|first2=F|last3=Lopez|first3=B|last4=Matter|first4=A|last5=Lagadec|first5=E|last6=Carbillet|first6=M|last7=Camera|first7=A|last8=Lamberts|first8=A|last9=Langlois|first9=M|last10=Milli|first10=J|last11=Avenhaus|first11=H|last12=Magnard|first12=Y|last13=Roux|first13=A|last14=Moulin|first14=T|last15=Carle|first15=M|last16=Sevin|first16=A|last17=Martinez|first17=P|last18=Abe|first18=L|last19=Ramos|first19=J|journal=Astronomy & Astrophysics|year=2018|volume=618|pages=A108|doi=10.1051/0004-6361/201832817|s2cid=119195253}}</ref>
| radius=3.29<ref name=soulain/>{{efn|name=radius}}
| luminosity=40,000<ref name=soulain/>
| temperature=45,000<ref name=soulain/>
| metal=
| rotation=
| gravity=
| component2 = OB
| mass2 = 20<ref name=soulain/>
| radius2=10<ref name=harries>{{cite journal|bibcode=2004MNRAS.350..565H|arxiv=astro-ph/0401574|title=Three-dimensional dust radiative-transfer models: The Pinwheel Nebula of WR 104|journal=Monthly Notices of the Royal Astronomical Society|volume=350|issue=2|pages=565|last1=Harries|first1=Tim J.|last2=Monnier|first2=John D.|last3=Symington|first3=Neil H.|last4=Kurosawa|first4=Ryuichi|year=2004|doi=10.1111/j.1365-2966.2004.07668.x|doi-access=free |s2cid=15291717}}</ref>
| luminosity2=80,000<ref name=soulain/>
| temperature2=30,000<ref name=soulain/><ref name=harries/>
| age2=
}}
{{Starbox detail|no_heading=y
| component1 = B
| mass = 
| radius = 7.98<ref name=soulain/>{{efn|name=radius}}
| luminosity = 68,000<ref name=soulain/>
| temperature = ≥33,000<ref name=soulain/>
}}
{{Starbox catalog
| names= [[Variable star designation|V5097]]&nbsp;Sgr, [[IRAS]]&nbsp;17590-2337, [[USNO|UCAC]]2&nbsp;22296214, [[Catalog of Stellar Identifications|CSI]]−23-17590, [[Two-Micron Sky Survey|IRC]]&nbsp;−20417, [[RAFGL]]&nbsp;2048, [[Midcourse Space Experiment|MSX6C]]&nbsp;G006.4432-00.4858, Ve&nbsp;2-45
}}
{{Starbox reference
| Simbad=WR+104
}}
{{Starbox end}}
{{Sky|18|02|04.07|-|23|37|41.2|80000000}}
'''WR 104''' is a [[triple star]] system located about {{convert|2580|pc|ly}} from [[Earth]]. The primary [[star]] is a [[Wolf–Rayet star]] (abbreviated as WR), which has a B0.5 [[main sequence]] star in close orbit and another more distant fainter companion.

The WR star is surrounded by a distinctive spiral [[Wolf–Rayet nebula]], often referred to as a pinwheel nebula. The rotational axis of the binary system, and likely of the two closest stars, is directed approximately towards Earth. Within the next few hundred thousand years, the Wolf–Rayet star is predicted to experience a core-collapse [[supernova]] with a small chance of producing a long-duration [[gamma-ray burst]].

The possibility of a supernova explosion from WR 104 having destructive consequences for life on Earth stirred interest in the mass media, and several popular science articles have been issued in the press since 2008. Some articles decide to reject the catastrophic scenario, while others leave it as an open question.<ref>{{cite web|last1=Plait|first1=Phil|title=WR 104: A nearby gamma-ray burst?|url=https://www.discovermagazine.com/the-sciences/wr-104-a-nearby-gamma-ray-burst|magazine=[[Discover (magazine)|Discover magazine]]|access-date=13 October 2022|date=3 March 2008|archive-date=March 23, 2020|archive-url=https://web.archive.org/web/20200323040802/https://www.discovermagazine.com/the-sciences/wr-104-a-nearby-gamma-ray-burst|url-status=live}}</ref><ref>{{cite news|last1=Sanderson|first1=Katharine|title='Death Star' found pointing at Earth|url=http://www.nature.com/news/2008/080306/full/news.2008.653.html|access-date=27 July 2016|magazine=Nature|date=6 March 2008|archive-date=June 5, 2017|archive-url=https://web.archive.org/web/20170605032809/http://www.nature.com/news/2008/080306/full/news.2008.653.html|url-status=live}}</ref><ref>{{cite news|last1=Q. Choi|first1=Charles|title=Real Death Star Could Strike Earth|url=http://www.space.com/5081-real-death-star-strike-earth.html|access-date=27 July 2016|website=Space.com|date=10 March 2008|archive-date=August 10, 2016|archive-url=https://web.archive.org/web/20160810233000/http://www.space.com/5081-real-death-star-strike-earth.html|url-status=live}}</ref><ref>{{cite news|last1=Kluger|first1=Jeffrey|title=The Super-Duper, Planet-Frying, Exploding Star That's Not Going to Hurt Us, So Please Stop Worrying About It|url=https://science.time.com/2012/12/21/the-super-duper-planet-frying-exploding-star-thats-not-going-to-hurt-us-so-please-stop-worrying-about-it/|access-date=27 July 2016|magazine=[[Time Magazine]]|date=21 December 2012|archive-date=December 21, 2017|archive-url=https://web.archive.org/web/20171221000429/http://science.time.com/2012/12/21/the-super-duper-planet-frying-exploding-star-thats-not-going-to-hurt-us-so-please-stop-worrying-about-it/|url-status=live}}</ref>

==System==
The Wolf–Rayet star that produces the characteristic emission line spectrum of WR 104 has a resolved companion and an unresolved spectroscopic companion, forming a triple system.

The spectroscopic pair consists of the Wolf–Rayet star and a B0.5 [[main sequence]] star.  The WR star is visually 0.3 magnitudes fainter than the main sequence star, although the WR star is typically considered the primary, as it dominates the appearance of the spectrum and is more luminous.  The two are in a nearly circular orbit separated by about 2 [[astronomical unit|AU]], which would be about one milli-arcsecond at the assumed distance.<ref name=wallace>{{cite journal|bibcode=2002ASPC..260..407W|title=Hubble Space Telescope Detection of Binary Companions Around Three WC9 Stars: WR 98a, WR 104, and WR 112|journal=Interacting Winds from Massive Stars. ASP Conference Proceedings|volume=260|pages=407|last1=Wallace|first1=Debra J.|last2=Moffat|first2=Anthony F. J.|last3=Shara|first3=Michael M.|year=2002}}</ref> The two stars orbit every 241.5 days with a small inclination (i.e. nearly face-on).<ref name=lamberts/>

The visually resolved companion is 1.5 magnitudes fainter than the combined [[spectroscopic binary|spectroscopic pair]] and almost one arc-second away.  It is thought to be physically associated, although orbital motion has not been observed.  From the colour and brightness, it is expected to be a hot main sequence star.<ref name=wallace/>

==Structure==
The rotational axis of the binary system is directed approximately towards Earth at an estimated inclination of 0 to 16 degrees. This provides a fortunate viewing angle for observing the binary system and its dynamics.<ref name=tuthill08/>

[[File:V5097SgrLightCurve.png|thumb|left|Broadband optical and [[Photometric_system#Photometric_letters|visual band]] [[light curve]]s for V5097 Sagittarii. The main plot shows the long-term variability and the inset plot shows the periodic variability. Adapted from Kato ''et al.'' (2002)<ref name="Kato2002"/>]]
Discovered as part of the [[W. M. Keck Observatory|Keck]] [[aperture masking interferometry|Aperture Masking Experiment]]<ref>{{cite journal |last1=Tuthill |first1=Peter G. |last2=Monnier |first2=John D. |last3=Danchi |first3=William C. |title=A dusty pinwheel nebula around the massive star WR104 |journal=Nature |date=1 April 1999 |volume=398 |issue=6727 |pages=487–489 |doi=10.1038/19033 |arxiv=astro-ph/9904092 |bibcode=1999Natur.398..487T |s2cid=4373103 |url=https://ui.adsabs.harvard.edu/abs/1999Natur.398..487T/abstract |issn=0028-0836 |access-date=February 22, 2023 |archive-date=February 22, 2023 |archive-url=https://web.archive.org/web/20230222080308/https://ui.adsabs.harvard.edu/abs/1999Natur.398..487T/abstract |url-status=live }}</ref> WR 104 is surrounded by a distinctive dusty Wolf–Rayet nebula over 200 [[astronomical unit]]s in diameter formed by interaction between the [[stellar wind]]s of the two stars as they rotate and orbit. The spiral appearance of the nebula has led to the name Pinwheel Nebula being used.<ref name=harries/> The spiral structure of the nebula is composed of dust that would be prevented from forming by WR 104's intense radiation were it not for the star's companion. The region where the stellar wind from the two massive stars interacts compresses the material enough for the [[Cosmic dust|dust]] to form, and the rotation of the system causes the spiral-shaped pattern.<ref name=tuthill99>{{Cite journal | doi = 10.1038/19033| year = 1999| last1 = Tuthill | first1 = P. G. | title = A dusty pinwheel nebula around the massive star WR104| journal = Nature| volume = 398| issue = 6727| pages = 487–489| last2 = Monnier | first2 = J. D. | last3 = Danchi | first3 = W. C. | bibcode = 1999Natur.398..487T|arxiv = astro-ph/9904092 | s2cid = 4373103}}</ref>  The round appearance of the spiral leads to the conclusion that the system is seen almost pole on, and an almost circular [[orbital period]] of 220 days had been assumed from the pinwheel outflow pattern.<ref name=tuthill08>{{Cite journal | doi = 10.1086/527286| title = The Prototype Colliding-Wind Pinwheel WR 104| journal = The Astrophysical Journal| volume = 675| pages = 698–710| year = 2008| last1 = Tuthill | first1 = P. G. | last2 = Monnier | first2 = J. D. | last3 = Lawrance | first3 = N. | last4 = Danchi | first4 = W. C. | last5 = Owocki | first5 = S. P. | last6 = Gayley | first6 = K. G. | issue = 1| bibcode = 2008ApJ...675..698T|arxiv = 0712.2111 | s2cid = 119293391}}</ref>

WR 104 shows frequent [[eclipse]] events as well as other irregular variations in brightness. The undisturbed apparent magnitude is around 12.7, but the star is rarely at that level. The eclipses are believed to be caused by dust formed from expelled material, not by the companion star.<ref name=williams2014/>

== Supernova progenitor==
Both stars in the WR 104 system are predicted to end their days as [[core-collapse supernova]]e. The Wolf–Rayet star is in the final phase of its life cycle and is expected to turn into a supernova much sooner than the OB star. It is predicted to occur at some point within the next few hundred thousand years.<ref name=tuthill08/> With the relatively close proximity to the Solar System, the question of whether WR 104 will pose a future danger to life on Earth has been raised.<ref name=hill>{{cite journal|bibcode=2009AAS...21334103H|title=WR 104: Are We Looking Down the Gun Barrel of a Future GRB?|journal=American Astronomical Society|volume=213|pages=341.03|last1=Hill|first1=Grant M.|year=2009}}</ref>

=== Gamma-ray burst ===
Apart from a core-collapse supernova, astrophysicists have speculated about whether WR 104 has the potential to cause a [[gamma-ray burst]] (GRB) at the end of its life.<ref name=grafener>{{cite journal|bibcode=2012A&A...547A..83G|arxiv=1210.1153|title=Rotating Wolf–Rayet stars in a post RSG/LBV phase. An evolutionary channel towards long-duration GRBs?|journal=Astronomy & Astrophysics|volume=547|pages=A83|last1=Gräfener|first1=G.|last2=Vink|first2=J. S.|last3=Harries|first3=T. J.|last4=Langer|first4=N.|year=2012|doi=10.1051/0004-6361/201118664|s2cid=55530420}}</ref><ref name=tuthill08/> The companion OB star certainly has the potential, but the Wolf–Rayet star is likely to go supernova much sooner. There remain too many uncertainties and unknown parameters for any reliable prediction, and only sketchy estimates of a GRB scenario for WR 104 have been published.<ref name=tuthill08/>

Wolf–Rayet stars with a sufficiently high spin velocity, prior to going supernova, could produce a long duration gamma ray burst, beaming high energy radiation along its rotational axis in two oppositely directed [[relativistic jet]]s. Presently, mechanisms for the generation of GRB emissions are not fully understood, but it is considered that there is a small chance that the Wolf–Rayet component of WR 104 may become one when it goes supernova.<ref name=tuthill08/>

===Effects on Earth===

According to available astrophysical data for both WR 104 and its companion, eventually both stars will finally be destroyed as highly directional anisotropic [[supernova]]e, producing concentrated radiative emissions as narrow [[relativistic jets]].<ref>{{cite journal|author1=Wehrle|first=A.E.|author-link=Ann E. Wehrle|author2=Zacharias, N.|author3=Johnston, K.|display-authors=etal|date=11 Feb 2009|title=What is the structure of Relativistic Jets in AGN on Scales of Light Days?|url=http://www.nrao.edu/A2010/whitepapers/rac/Wehrle_AGN_jets_GCT.pdf|journal=Astro2010: The Astronomy and Astrophysics Decadal Survey|volume=2010|pages=310|bibcode=2009astro2010S.310W|access-date=February 5, 2017|archive-date=November 7, 2016|archive-url=https://web.archive.org/web/20161107230012/http://www.nrao.edu/A2010/whitepapers/rac/Wehrle_AGN_jets_GCT.pdf|url-status=live}}</ref> 
Theoretical studies of such supernovae suggest jet formation aligns with the rotational axes of its progenitor star and its eventual [[compact star|stellar remnant]], and will preferentially eject matter along their polar axes.<ref name=tuthill08/>

If these jets happen to be aimed towards our solar system, its consequences could significantly harm life on Earth and its biosphere, whose true impact depends on the amount of radiation received, the number of energetic particles and the source's distance. Knowing that the inclination of the binary system containing WR 104 is roughly 12° relative to line of sight, and assuming both stars have their rotational axes similarly orientated, suggests some potential risk.<ref name=tuthill_subject_expert_faq>{{cite web|last1=Tuthill|first1=Peter|title=WR 104: Technical Questions|url=http://www.physics.usyd.edu.au/~gekko/pinwheel/tech_faq.html|access-date=20 December 2015|archive-date=April 3, 2018|archive-url=https://web.archive.org/web/20180403160554/http://www.physics.usyd.edu.au/~gekko/pinwheel/tech_faq.html|url-status=live}}</ref> Recent studies suggest these effects pose a "highly unlikely" danger to life on Earth, with which, as stated by Australian astronomer [[Peter Tuthill (astronomer)|Peter Tuthill]], the Wolf–Rayet star would have to undergo an extraordinary string of successive events:<ref name=tuthill_subject_expert_faq/>

# The Wolf–Rayet star would have to generate a [[gamma-ray burst]] (GRB); however, these events are mostly associated with galaxies with a low [[metallicity]] and have not yet been observed in our [[Milky Way Galaxy]]. Some astronomers believe it unlikely that WR 104 will generate a GRB;<ref>{{cite journal|bibcode=2007Ap&SS.311..177V|arxiv=0704.0659|title=Long gamma-ray burst progenitors: Boundary conditions and binary models|journal=Astrophysics and Space Science|volume=311|pages=177–183|last1=Van Den Heuvel|first1=E. P. J.|last2=Yoon|first2=S.-C.|year=2007|issue=1–3|doi=10.1007/s10509-007-9583-8|s2cid=38670919}}</ref> Tuthill tentatively estimates the probability for any kind of GRB event is around the level of one percent, but cautions more research is needed to be confident.
# The rotational axis of the Wolf–Rayet star would have to be pointed in the direction of Earth. The star's axis is estimated to be close to the axis of the binary orbit of WR 104. Observations of the spiral plume are consistent with an orbital pole angle of anywhere from 0 to 16 degrees relative to the Earth, but a spectrographic observation suggest a significantly larger and therefore less dangerous angle of 30°–40° (possibly as much as 45°).<ref>{{cite web|title=WR 104 Won't Kill Us After All|url=http://www.universetoday.com/23342/wr-104-wont-kill-us-after-all/|website=Universe Today|date=January 7, 2009|access-date=July 27, 2016|archive-date=September 19, 2012|archive-url=https://archive.today/20120919074741/http://www.universetoday.com/23342/wr-104-wont-kill-us-after-all/|url-status=live}}</ref> Estimates of the "opening angle" jet's arc currently range from 2 to 20 degrees. (Note: The "opening angle" is the total angular span of the jet, not the angular span from the axis to one side. Earth would therefore only be in the intersecting path if the actual angle of the star's axis relative to Earth is less than ''half'' the opening angle.)
# The jet would have to reach far enough in order to damage life on Earth. The narrower the jet appears, the farther it will reach, but the less likely it is to hit Earth.

== Notes ==
{{notelist|refs=

{{efn | name=radius | Applying the [[Stefan–Boltzmann law]] with a nominal [[sun|solar]] [[effective temperature]] of 5,772&nbsp;[[Kelvin|K]]: 
:<math>\sqrt{(5772/45000)^4 * 40,000} = 3.29\ R\odot</math>
:<math>\sqrt{(5772/33000)^4 * 68,000} = 7.978\ R\odot</math>}}

}}

==References==
{{reflist|2|refs=

<ref name="Kato2002">{{cite journal |last1=Kato |first1=Taichi |last2=Haseda |first2=Katsumi |last3=Yamaoka |first3=Hitoshi |last4=Takamizawa |first4=Kesao |title=Discovery of Extremely Large-Amplitude Quasi-Periodic Photometric Variability in a WC9-Type Wolf–Rayet Binary, WR 104 |journal=Publications of the Astronomical Society of Japan |date=August 2002 |volume=54 |issue=4 |pages=L51–L54 |doi=10.1093/pasj/54.4.L51 |arxiv=astro-ph/0205525 }}</ref>

}}

==External links==
*{{WikiSky}}
*[http://www.physics.usyd.edu.au/~gekko/pinwheel.html University of Sydney (Keck Observatory) page]
*{{APOD |date=June 3, 2014 |title=WR 104: A Pinwheel Star System}}

{{Stars of Sagittarius}}

{{DEFAULTSORT:WR 104}}
[[Category:Wolf–Rayet stars]]
[[Category:Pinwheel nebulae]]
[[Category:Sagittarius (constellation)]]
[[Category:Objects with variable star designations|Sagittarii, V5097]]
[[Category:Astronomical objects discovered in 1998]]
[[Category:IRAS catalogue objects]]
[[Category:Spectroscopic binaries]]
[[Category:Triple star systems]]
[[Category:B-type main-sequence stars]]