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]
Characteristics
Spectral type WC9d/B0.5V[3]
Astrometry
Distance2,300[3] pc
Absolute magnitude (MV)−5.4 (−4.8 + −4.6)[4]
Details
Radius10[5] R☉
Luminosity150,000[5] L☉
Temperature40,000[5] 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 binary star system located about 7,500 light years from Earth, surrounded by a distinctive pinwheel nebula. The primary is a Wolf-Rayet star and the secondary is a main sequence OB star. Within the next few hundred thousand years, the system has a small (perhaps around one-percent) probability of firing a gamma-ray burst in the general direction of the Earth. In the unlikely event the system does fire such a burst, the burst is unlikely to hit and cause damage to the Earth.

Structure

WR 104 is surrounded by a distinctive dusty pinwheel nebula over 200 astronomical units long formed by interaction between the stellar winds of the two stars as they rotate and orbit. The spiral 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.[6] 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.[7]

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 by dust formed from expelled material, not by the companion star.[2] A third star, about 2 magnitudes fainter than the spectroscopic pair at visual wavelengths, has been resolved almost 1" distant.[8]

Potential gamma-ray bursts

The Wolf-Rayet star in WR 104 is expected to end its lifecycle in either a supernova or hypernova within the next few hundred thousand years.[9] A Wolf-Rayet star with a sufficiently high spin velocity could, at the end of its life, go hypernova rather than merely supernova and eject a deadly gamma-ray burst (GRB) from each pole. WR 104 is believed to have sufficient spin to create a small possibility of such a hypernova.[10][11]

Effects on Earth

It currently seems unlikely that a hypernova from WR 104 will ever pose a danger to the Earth.[9][10][12] According to astronomer Peter Tuthill, in order to damage the Earth, the Earth would have to undergo an extraordinary string of bad luck:[11]

  1. The Wolf-Rayet star would have to go hypernova, rather than supernova, and generate a GRB. It is not currently known whether WR 104 will go supernova or whether it will go hypernova, but because GRB-generated events are very rare in our galaxy, astronomers believe it unlikely WR 104 will generate a GRB. Peter 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. A pole of the Wolf-Rayet star, and thus one of the two GRB's ejected from opposite ends of the hypernova, would then have to be pointed directly at our planet. The star's pole is probably close to the pole of the binary orbit. Observations of the spiral plume are consistent with an orbital pole angle of anywhere from 0 to 16 degrees relative to the Earth, but spectographic observations suggest a significantly larger and 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 measure from side of the GRB to the other, not the measure from the axis to one side; therefore the Earth would only be in the path of the GRB if the actual angle of the star's pole relative to the Earth is less than half the opening angle. So for example, if the orbital angle were 8 degrees, and the "opening angle" were less than 16 degrees, then the Earth would not even be in the path of the GRB.)
  3. The unlikely GRB would then have to reach far enough to harm the Earth. The more narrow a GRB is, the farther it will reach, but the less likely its narrow beam will happen to hit the Earth.

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:1408.6759. Bibcode:2014MNRAS.445.1253W. doi:10.1093/mnras/stu1779. ISSN 0035-8711.
  3. 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.
  4. ↑ 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.
  5. 1 2 3 Sander, A.; Hamann, W. -R.; Todt, H. (2012). "The Galactic WC stars". Astronomy & Astrophysics 540: A144. arXiv:1201.6354. Bibcode:2012A&A...540A.144S. doi:10.1051/0004-6361/201117830.
  6. ↑ 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/9904092. Bibcode:1999Natur.398..487T. doi:10.1038/19033.
  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. arXiv:0712.2111. Bibcode:2008ApJ...675..698T. doi:10.1086/527286.
  8. ↑ 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.
  9. 1 2 Tuthill, Peter. "WR 104: The prototype Pinwheel Nebula". Retrieved 20 December 2015.
  10. 1 2 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 20 December 2015.
  11. 1 2 Tuthill, Peter. "WR 104: Technical Questions". Retrieved 20 December 2015.
  12. ↑ Plait, Phil (3 March 2008). "WR 104: A nearby gamma-ray burst?". Discover magazine. Retrieved 20 December 2015.

External links

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