WR 104

WR 104

WR 104
Observation data
Epoch 2000      Equinox 2000
Constellation Sagittarius
Right ascension 18h 02m 04.07s[1]
Declination −23° 37′ 41.2″[1]
Apparent magnitude (V) 13.28 (12.7 - 14.6)[2] + 15.36[3]
Characteristics
Spectral type WC9d/B0.5V[4]
Astrometry
Distance2,300[4] pc
Absolute magnitude (MV)−5.4 (−4.8 + −4.6)[5]
Orbit[6]
Period (P)241.5 days
Semi-major axis (a)2.34 AU
Eccentricity (e)< 0.06
Inclination (i)< 16°
Details
Luminosity250,000[7] L☉
WR
Radius10[8] R☉
Temperature40,000[8] K
OB
Radius10[9] R☉
Temperature30,000[9] K
Other designations
V5097 Sgr, IRAS 17590-2337, UCAC2 22296214, CSI-23-17590, IRC −20417, RAFGL 2048, MSX6C G006.4432-00.4858, Ve 2-45
Database references
SIMBADdata

Coordinates: 18h 02m 04.07s, −23° 37′ 41.2″

WR 104 is a triple star system located about 7,500 light years from Earth. The primary is a Wolf-Rayet star, with a B0.5 main sequence star in a close orbit and a more distant fainter star.

The WR star is surrounded by a distinctive Wolf–Rayet nebula, originally categorized as a pinwheel nebula and often referred to as the 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 explode as a core-collapse-supernova with a small chance of producing a long duration gamma-ray burst.

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 consist 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 AU, which would be about one milli-arcsecond at the assumed distance.[3] The two stars orbit every 241.5 days with a small inclination (i.e. nearly face-on).[6]

The visually resolved companion is 1.5 magnitudes fainter than the combined 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.[3]

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.[10]

WR 104 is surrounded by a distinctive dusty Wolf-Rayet nebula over 200 astronomical units in diameter formed by interaction between the stellar winds of the two stars as they rotate and orbit. The spiral structure of the nebula is composed of dust that would normally 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 dust to form, and the rotation of the system causes the spiral-shaped pattern.[11] 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.[10]

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.[2]

Supernova explosions

Both stars in the WR 104 system are predicted to end their days as core-collapse-supernovae. The Wolf-Rayet star is in the final phase of its life cycle and is expected to explode much sooner than the OB star. It is predicted to explode at some point within the next few hundred thousand years. 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.[10]

Gamma-ray burst

Apart from a core-collapse-supernova, astrophysicists have speculated about whether WR 104 has the potential to become a gamma-ray burst (GRB) at the end of its stars life cycles. The OB star certainly has the potential, but the Wolf-Rayet star, which is already at the end of its life cycle, is expected to explode much sooner and is therefore more important to consider for such a scenario. There remain too many uncertainties and unknown parameters for any reliable predictions, and only sketchy estimates of a GRB scenario for WR 104 has been published.[10]

Generally it is predicted that a Wolf-Rayet star with a sufficiently high spin velocity could, at the end of its life, produce a long duration GRB with two oppositely directed beams of high energy radiation along its rotational axis. The mechanisms for the production of a GRB are not fully understood, but it is thought that there is a small chance that the Wolf-Rayet component of WR 104 may produce one when it explodes as a supernova.[10]

Effects on Earth

If a supernova from WR 104 is isotropic, its destructive consequences for the biosphere on Earth are predicted to be negligible. If it happens to be highly anisotropic however, there is a risk that it might cause significant harm, in particular because it is generally assumed that the rotational axis of both stars are orientated in the same way as the binary system, with an estimated (but uncertain) 12 degrees inclination relative to Earth. Anisotropic supernovae concentrate their radiative emissions in jet-cones along their rotational axis, so this face-on alignment makes WR 104 potentially dangerous. According to the data about WR 104, both supernovae are expected to be anisotropic.[10]

Regarding a GRB from WR 104 specifically, only sketchy estimates have been published so far. To predict the potential consequences for life on Earth, a proper determination of the rotational axis inclination relative to Earth is considered the most vital issue in this regard.[10] If a beam of high energy radiation from a nearby GRB hits Earth, model calculations shows that it can have destructive consequences for the ecosystems. The range of destruction depends on the magnitude and distance of the burst and on how much of the radiation beam hits. It is currently "highly unlikely" that a GRB from WR 104 will pose a danger to life on Earth.[12]

According to astronomer Peter Tuthill, in order to damage life on Earth, the Wolf-Rayet star would have to undergo an extraordinary string of events:[12]

  1. The Wolf-Rayet star would have to generate a GRB. Because GRBs are associated with galaxies with a low metallicity and haven't yet been observed in our Milky Way Galaxy, astronomers believe it unlikely that WR 104 will generate a GRB.[13] Tuthill tentatively estimates the probability for any kind of GRB is around the level of one percent, but cautions more research is needed to be confident.
  2. The rotational axis of the Wolf-Rayet star, would have to be pointed in the direction of our planet. 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. Estimates of the "opening angle" of a GRB's arc currently range from 2 to 20 degrees. (Note: The "opening angle" is the total angular span of a GRB radiation beam, not the angular span from the axis to one side. Earth would therefore only be in the path of a GRB if the actual angle of the star's axis relative to Earth is less than half the opening angle.)
  3. The GRB would have to reach far enough in order to damage life on Earth. The more narrow a GRB radiation beam is, the farther it will reach, but the less likely it is to hit Earth.

In the press

The possibility of a supernova explosion from WR 104 with a destructive consequence for life on Earth has stirred interest in the mass media and several popular science articles have been issued in the press since 2008, mostly in the UK and the US. Some articles decide to reject the catastrophic scenario, while others leave it as an open question.[14][15][16][17][18]

References

  1. 1 2 Cutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; Beichman, C. A.; Carpenter, J. M.; Chester, T.; Cambresy, L.; Evans, T.; Fowler, J.; Gizis, J.; Howard, E.; Huchra, J.; Jarrett, T.; Kopan, E. L.; Kirkpatrick, J. D.; Light, R. M.; Marsh, K. A.; McCallon, H.; Schneider, S.; Stiening, R.; Sykes, M.; Weinberg, M.; Wheaton, W. A.; Wheelock, S.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". VizieR On-line Data Catalog: II/246. Originally published in: 2003yCat.2246....0C. 2246: 0. Bibcode:2003yCat.2246....0C.
  2. 1 2 Williams, P. M. (2014). "Eclipses and dust formation by WC9 type Wolf-Rayet stars". Monthly Notices of the Royal Astronomical Society. 445 (2): 1253–1260. arXiv:1408.6759Freely accessible. Bibcode:2014MNRAS.445.1253W. doi:10.1093/mnras/stu1779. ISSN 0035-8711.
  3. 1 2 3 Wallace, Debra J.; Moffat, Anthony F. J.; Shara, Michael M. (2002). "Hubble Space Telescope Detection of Binary Companions Around Three WC9 Stars: WR 98a, WR 104, and WR 112". Interacting Winds from Massive Stars. ASP Conference Proceedings. 260: 407. Bibcode:2002ASPC..260..407W.
  4. 1 2 Van Der Hucht, K. A. (2001). "The VIIth catalogue of galactic Wolf–Rayet stars". New Astronomy Reviews. 45 (3): 135. Bibcode:2001NewAR..45..135V. doi:10.1016/S1387-6473(00)00112-3.
  5. ↑ Williams, P. M.; van der Hucht, K. A. (2000). "Spectroscopy of WC9 Wolf-Rayet stars: a search for companions". Monthly Notices of the Royal Astronomical Society. 314 (1): 23–32. Bibcode:2000MNRAS.314...23W. doi:10.1046/j.1365-8711.2000.03332.x. ISSN 0035-8711.
  6. 1 2 Lamberts, A.; Dubus, G.; Lesur, G.; Fromang, S. (2012). "Impact of orbital motion on the structure and stability of adiabatic shocks in colliding wind binaries". Astronomy & Astrophysics. 546: A60. arXiv:1202.2060Freely accessible. Bibcode:2012A&A...546A..60L. doi:10.1051/0004-6361/201219006.
  7. ↑ Monnier, J. D.; Tuthill, P. G.; Danchi, W. C.; Murphy, N.; Harries, T. J. (2007). "The Keck Aperture-masking Experiment: Near-Infrared Sizes of Dusty Wolf-Rayet Stars". The Astrophysical Journal. 655 (2): 1033. arXiv:astro-ph/0610437Freely accessible. Bibcode:2007ApJ...655.1033M. doi:10.1086/509873.
  8. 1 2 Sander, A.; Hamann, W. -R.; Todt, H. (2012). "The Galactic WC stars". Astronomy & Astrophysics. 540: A144. arXiv:1201.6354Freely accessible. Bibcode:2012A&A...540A.144S. doi:10.1051/0004-6361/201117830.
  9. 1 2 Harries, Tim J.; Monnier, John D.; Symington, Neil H.; Kurosawa, Ryuichi (2004). "Three-dimensional dust radiative-transfer models: The Pinwheel Nebula of WR 104". Monthly Notices of the Royal Astronomical Society. 350 (2): 565. arXiv:astro-ph/0401574Freely accessible. Bibcode:2004MNRAS.350..565H. doi:10.1111/j.1365-2966.2004.07668.x.
  10. 1 2 3 4 5 6 7 Tuthill, P. G.; Monnier, J. D.; Lawrance, N.; Danchi, W. C.; Owocki, S. P.; Gayley, K. G. (2008). "The Prototype Colliding‐Wind Pinwheel WR 104". The Astrophysical Journal. 675: 698–710. arXiv:0712.2111Freely accessible. Bibcode:2008ApJ...675..698T. doi:10.1086/527286.
  11. ↑ Tuthill, P. G.; Monnier, J. D.; Danchi, W. C. (1999). "A dusty pinwheel nebula around the massive star WR104". Nature. 398 (6727): 487. arXiv:astro-ph/9904092Freely accessible. Bibcode:1999Natur.398..487T. doi:10.1038/19033.
  12. 1 2 Tuthill, Peter. "WR 104: Technical Questions". Retrieved 20 December 2015.
  13. ↑ Van Den Heuvel, E. P. J.; Yoon, S.-C. (2007). "Long gamma-ray burst progenitors: Boundary conditions and binary models". Astrophysics and Space Science. 311: 177. arXiv:0704.0659Freely accessible. Bibcode:2007Ap&SS.311..177V. doi:10.1007/s10509-007-9583-8.
  14. ↑ Plait, Phil (3 March 2008). "WR 104: A nearby gamma-ray burst?". Discover magazine. Retrieved 20 December 2015.
  15. ↑ Sanderson, Katharine (6 March 2008). "'Death Star' found pointing at Earth". Nature. Retrieved 27 July 2016.
  16. ↑ Q. Choi, Charles (10 March 2008). "Real Death Star Could Strike Earth". Space.com. Retrieved 27 July 2016.
  17. ↑ Kluger, Jeffrey (21 December 2012). "The Super-Duper, Planet-Frying, Exploding Star That's Not Going to Hurt Us, So Please Stop Worrying About It". Time Magazine. Retrieved 27 July 2016.
  18. ↑ O'Neill, Ian (24 December 2015). "WR 104 Won't Kill Us After All". Universe Today. Retrieved 27 July 2016.

Sources

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