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Coordinates: Sky map 16h 00m 50.5s, −51° 42′ 45″
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{{Starbox catalog
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| names = Apep
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{{Starbox reference
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Revision as of 16:40, 22 November 2018

Apep (star system)

Infrared image by the Very Large Telescope[a]
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Norma
Right ascension 16h 00m 50.5s
Declination −51° 42′ 45″
Apparent magnitude (V) 17.5
Characteristics
Evolutionary stage WR binary
Apparent magnitude (J) 10.2
Apparent magnitude (K) 6.9
Astrometry
Distance~8,000 ly
(2,400+200
−500 pc)
Orbit
Period (P)~100 yr
Other designations
Apep
Database references
SIMBADdata

2XMM J160050.7–514245, nicknamed Apep, is a triple star system containing a Wolf–Rayet binary and a hot supergiant, located in the constellation of Norma. Named after the eponymous serpent deity from Egyptian mythology, the star system is surrounded by a vast complex of stellar wind and cosmic dust thrown into space by the fast rotation speed of the binary's primary star and formed into a "pinwheel" shape by the secondary star's influence. The system was first discovered with the XMM-Newton telescope in August 2004, and ground-based studies of the system from 2016 to 2018 concluded that the system was the first Gamma-ray burst progenitor candidate in the Milky Way galaxy. The primary star's axial tilt of 30° away from Earth means that a potential Gamma-ray burst would not impact life on Earth.

Nomenclature

2XMM J160050.7–514245 is the name for the system in the XMM-Newton Serendipitous Source Catalogue (2XMM), a star catalog of x-ray sources observed by the XMM-Newton space telescope.[3] The proper name "Apep" was given to the system by a team of astronomers led by Joseph Callingham of ASTRON, who studied the system between 2016 and 2018 and published a scientific paper on their observations.[4][5] It was named after the eponymous mortal enemy of the deity of the sun Ra in Egyptian mythology, who was often illustrated as a giant serpent; their rivalry was described by Callingham's team as "an apt allusion" to the appearance of the system and its stellar wind in infrared as "a star embattled within a dragon’s coils".[4][6]

Characteristics

2XMM J160050.7–514245 is a triple star system[5][7] containing a Wolf–Rayet binary in orbit around a barycenter with a period of ~100 years each,[8] and a third hot supergiant star orbiting the binary at a distance of ~1,700 astronomical units and a period of >10,000 years.[9] A vast complex of stellar wind and cosmic dust surrounds the system,[6][10][7] resembling WR 104, another Wolf-Rayet star system producing a pinwheel nebula.[11] The wind, travelling at a velocity of 12,000,000 km/h (7,500,000 mph),[5][10] and dust travelling at 2,000,000 km/h (1,200,000 mph) at the edge of the system, infer 2XMM J160050.7–514245 A's extremely fast rotation rate, in which its surface gravity is close to being balanced by its centrifugal force outwards.[7][12] A produces faster stellar winds from its poles and slower winds from its equator, and the equatorial dust's interaction with 2XMM J160050.7–514245 B produces the system's "pinwheel" shape.[13][14] Wolf–Rayet stars with fast rotations are theoretically capable of producing a Gamma-ray burst during a supernova, and the system has been identified as a progenitor for a Gamma-ray burst.[15] A's axis is estimated to be tilted 30° away from Earth, meaning that a potential Gamma-ray burst from the system would not pose a threat to life on Earth.[16]

Observation

Map of the constellation Norma
Location of 2XMM J160050.7–514245 in the constellation Norma

2XMM J160050.7–514245 is located in the constellation of Norma, at a right ascension of 16h 00m 50.5s and declination of −51° 42′ 45″,[1] and estimated to be at a distance of ~2.4 kiloparsecs[17] (~8,000 light years[8][18]) from Earth, with a potential discrepancy of +0.2 and -0.5 kiloparsecs at its estimated visual extinction of 11.4.[17] The system can be resolved into two components, the Wolf–Rayet binary 2XMM J160050.7–514245 A and B, and the supergiant 2XMM J160050.7–514245 C.[19] The apparent magnitude of the system is 17.5, with the apparent magnitude of a resolved A and B being 19.0 and a resolved C being 17.8.[20] Surveys conducted with European Southern Observatory (ESO)'s SINFONI telescope measured the apparent magnitude in the infrared J band for A and B as 10.2±0.2, and for C as 9.6±0.2.[21] SINFONI also measured the apparent magnitude of the system in the K band as 6.9±0.2 for A and B and 8.1±0.2 for C,[22] in the L band as 4.7±0.1 for A and B and 7.3±0.1 for C,[22] and in the M band as 4.4±0.3 for A and B and 7.0±0.2 for C.[22] SINFONI observations further detailed that C is possibly a conventional B1Ia+ high luminosity star.[23] A and B show a typical spectrum from a WC7 star,[24] but with additional WN4 or WN5 star features theorised to be from B; if confirmed, this would make 2XMM J160050.7–514245 a rare binary system of WR stars.[25] An alternative hypothesis also based on SINFONI data proposes that the spectra could all be from an unusual transitional WN/WC star, and that C would then be a conventional OB star.[26]

The system was the first Gamma-ray burst progenitor candidate to be discovered in the Milky Way galaxy,[6] although it had not been known as such when it was first discovered as an x-ray source with the XMM-Newton space telescope on 10 August 2004, and when further observations with XMM-Newton and the Chandra space telescope were made in the following years.[27] 2XMM J160050.7–514245's Wolf–Rayet binary nature was discovered during a survey conducted by Joe Callingham of ASTRON, with the Molonglo Observatory Synthesis Telescope,[10] and later confirmed with follow-up observations made with the Anglo-Australian Telescope.[18] Observations were made between 2016 and 2018 with the European Southern Observatory's Very Large Telescope as part of an international study of the system led by Callingham with involvement from the University of Edinburgh, the University of New South Wales, the University of Sheffield, and the University of Sydney.[14] Their scientific paper, published in Nature Astronomy on 19 November 2018,[13] concluded that the system was a progenitor for a Gamma-ray burst.[7][28] It had been previously assumed that such systems were only found in galaxies younger than the Milky Way.[14]

See also

References

Notes

  1. ^ A composite of two infrared images taken by the European Southern Observatory's Very Large Telescope on 13 August 2016 – one of the stars in the center of the system taken by the NACO instrument in a wavelength of 2.24 micrometres, and one of the surrounding dust and gas cloud taken by the VISIR instrument in a wavelength of 8.9 micrometers. The image measures 1.8 × 1.8 arcseconds across.[1][2]

Sources

  1. Callingham, J. R.; Tuthill, P. G.; Pope, B. J. S.; Williams, P. M.; Crowther, P. A.; Edwards, M.; Norris, B.; Kedziora-Chudczer, L. (24 September 2018). "Anisotropic winds in a Wolf–Rayet binary identify a potential gamma-ray burst progenitor" (PDF). University of Sydney School of Physics. Archived from the original (PDF) on 20 November 2018. Retrieved 20 November 2018. {{cite web}}: Invalid |ref=harv (help); Unknown parameter |dead-url= ignored (|url-status= suggested) (help)
  2. Plait, Phil (19 November 2018). "Bad Astronomy: Is this cosmic sprinkler surrounding galaxy's next gamma-ray burst?". Syfy Wire. Archived from the original on 22 November 2018. Retrieved 22 November 2018. {{cite web}}: Invalid |ref=harv (help); Unknown parameter |dead-url= ignored (|url-status= suggested) (help)

Citations

  1. ^ a b Callingham et al. 2018, page 3, "Figure 1. VISIR 8.9 μm image of Apep taken on 2016 August 13, displaying the exotic dust pattern being sculpted by the system. The 2.24 μm NACO image of the region bounded by the blue box, of dimension 1.8" × 1.8", is shown in the upper right corner."
  2. ^ Plait 2018, "This is combination of two infrared images; what you see as blue is at a wavelength of 2.24 microns [...] The red is at 8.9 microns, where warm dust tends to glow. Both were taken using the Very Large Telescope in Chile."
  3. ^ XMM-Newton Survey Science Centre (20 August 2008). "The XMM-Newton Serendipitous Source Catalogue: 2XMM User Guide". University of Leicester Department of Physics and Astronomy. Archived from the original on 20 November 2018. Retrieved 20 November 2018. 2XMM is a catalogue of serendipitous X-ray sources from the European Space Agency's (ESA) XMM-Newton observatory {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  4. ^ a b Callingham et al. 2018, page 3, "we here adopt the moniker "Apep" after the sinuous form of this infrared plume [...] The serpent diety from Egyptian mythology; mortal enemy of sun god Ra. We think this is an apt allusion to the image which evokes a star embattled within a dragon’s coils."
  5. ^ a b c Dvorsky, George (19 November 2018). "Stunning Pinwheel Nebula Is a Cosmic Cataclysm in the Making". Gizmodo. Archived from the original on 20 November 2018. Retrieved 20 November 2018. ...but to the researchers who recently investigated this enigmatic object, it's simply "Apep" [...] The speed of gas within the nebula was clocked at 12 million kilometers per hour [...] featuring a massive triple star system at its core—a binary pair and a lone star... {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  6. ^ a b c Letzter, Rafi (19 November 2018). "This Spinning, Snakelike Star System Might Blast Gamma Rays into the Milky Way When It Dies". Live Science. Archived from the original on 20 November 2018. Retrieved 20 November 2018. For the first time, astronomers have found a star system in our galaxy that could produce a gamma-ray burst [...] the researchers nicknamed it "Apep" after the Egyptian snake-deity of chaos. [...] The name works nicely for the system, which is surrounded by long, fiery pinwheels of matter cast out into space... {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  7. ^ a b c d Carpineti, Alfredo (19 November 2018). "This 'Cosmic Serpent' Is The First System Of Its Kind To Be Discovered In Our Galaxy". IFL Science!. Archived from the original on 20 November 2018. Retrieved 20 November 2018. Three stars are in this picture, although the two Wolf-Rayet stars look like a single one in the center [...] the winds are moving at 12 million kilometers (7.5 million miles) per hour. [...] The observations were possible thanks to the Very Large Telescope [...] the dust at the edge of the system is moving at the slower pace of 2 million kilometers (1.2 million miles) per hour. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  8. ^ a b Griffin, Andrew (19 November 2018). "Huge star system near Earth could produce one of the most spectacular explosions in the universe". The Independent. Archived from the original on 20 November 2018. Retrieved 20 November 2018. The swirling cloud of dust is a mere 8,000 light years from Earth is a vast system made up of two shockingly bright stars. [...] The two bright stars orbit each other every hundred years or so, according to the researchers. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  9. ^ Plait 2018, "At 250 billion kilometers out from the bright star (about ten times the distance of Neptune from the Sun), it would take more than 10,000 years to circle it once..."
  10. ^ a b c Strom, Marcus (20 November 2018). "Doomed star in Milky Way threatens rare gamma-ray burst". University of Sydney. Archived from the original on 20 November 2018. Retrieved 20 November 2018. ...the astronomers have measured the velocity of the stellar winds as fast as 12 million kilometres an hour, about 1 percent the speed of light. [...] We discovered this star as an outlier in a survey with a radio telescope operated by the University of Sydney. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  11. ^ Plait 2018, "Sometimes, if they are in a tight binary, you get a pinwheel. The most famous example of that is WR 104..."
  12. ^ Plait 2018, "The astronomers who observed it think that the primary (brighter) one is spinning extremely rapidly, so fast it's nearly at the breakup rate — in other words, spinning so fast that the gravity of the star at the surface is nearly balanced by the centrifugal force outwards."
  13. ^ a b Weule, Genelle (20 November 2018). "Spectacular cosmic pinwheel is a 'ticking bomb' set to blast gamma rays across the Milky Way". ABC News Australia. Archived from the original on 20 November 2018. Retrieved 20 November 2018. Writing in the journal Nature Astronomy [...] the most violent star is creating stellar winds at two speeds — fast at the poles, slow at the equator [...] the beautiful pinwheel of blazing dust is created not by the fast polar winds, but by the turbulence that arises when the second star in the central engine passes through that first star's slow-moving equatorial wind. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  14. ^ a b c Devitt, James (19 November 2018). "Scientists Discover New "Pinwheel" Star System". New York University. Archived from the original on 20 November 2018. Retrieved 20 November 2018. "It was not expected such a system would be found in our galaxy—only in younger galaxies much further away," [...] The discovery of the system [...] also included scientists from the Netherlands Institute for Radio Astronomy, the University of Sydney, the University of Edinburgh, the University of Sheffield, and the University of New South Wales. [...] is adorned with a dust "pinwheel"— whose strangely slow motion suggests current theories on star deaths may be incomplete. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  15. ^ Clery, Daniel (20 November 2018). "Massive star system primed for intense explosion". Science. Archived from the original on 20 November 2018. Retrieved 20 November 2018. One of stars is an unusually massive sun known as a Wolf-Rayet star. When such stars run out of fuel, they collapse, causing a supernova explosion. Theorists believe that if the Wolf-Rayet star is also spinning fast, the explosion will produce intense jets of gamma rays out of either pole... {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  16. ^ Plait 2018, "The best fitting model by the astronomers has the axis of the star tipped away from us by about 30°, so we'd miss the full brunt of the blast."
  17. ^ a b Callingham et al. 2018, page 18–19, "If we use the visual extinction AV = 11.4 [...] we need a distance of d = 2.4+0.2
    −0.5     to get realistic absolute magnitudes for the components. [...] Despite these uncertainties, all lines of evidence suggest that Apep is located [less-than around] 4.5 kpc, and likely around d ≈ 2.4 kpc."
  18. ^ a b Mannix, Liam (20 November 2018). "Super-powerful interstellar 'ticking time bomb' found not far from Earth". The Sydney Morning Herald. Archived from the original on 20 November 2018. Retrieved 20 November 2018. In a part of the Milky Way 8000-odd light-years away [...] The system was spotted by PhD student Dr Joe Callingham while he was sorting through data, and later confirmed using the Anglo-Australian Telescope at Coonabarabran in regional NSW. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  19. ^ Callingham et al. 2018, page 2, "The 2.24μm NACO observation (Figure 1, inset) resolves Apep into a 0.739" ± 0.002" binary with a fainter companion to the North."
  20. ^ Callingham et al. 2018, page 18, "...the known visual magnitude V = 17.5 for Apep (V = 17.8 for the OB supergiant that is the northern companion and V = 19.0 for the Central Engine)..."
  21. ^ Callingham et al. 2018, page 14, "Apep was resolved by SINFONI [...] We summed the J-band data over the Central Engine and northern companion to derive the J-band magnitudes of 10.2±0.2 and 9.6±0.2, respectively."
  22. ^ a b c Callingham et al. 2018, page 22, "Supplementary Information Table 2. Summary of the NACO observations of Apep. Separation refers to the angular separation between the Central Engine and northern companion, identified in the inset of Figure 1. The uncertainties reported are for 90% confidence."
  23. ^ Callingham et al. 2018, page 21, "Despite this, we favour the northern companion being an B1 Ia+ supergiant but further observations, particularly optical spectra, are necessary to confirm this spectral type."
  24. ^ Callingham et al. 2018, page 20, "...the spectrum of Apep shows stronger He II and weaker C IV line emission than is stereotypical for a WC7 star."
  25. ^ Callingham et al. 2018, page 20, "The weakness in the J-band, where dust emission is negligible [...] points to the additional continuum from a companion star. The abnormal strength of the He II lines for a WC7 star suggests an early WN sub-type companion. The absence of N V and relative weakness of He I, and with comparison to WN spectra, implies the presence of a subtype WN4 or WN5 star. Double WR binaries are, however, rare, with very few known."
  26. ^ Callingham et al. 2018, page 21, "An alternative spectral subtype classification to the WC7+WN4-5 model, that equally well describes the spectra shown in Figure 2, is that of a WR star in the brief transitory phase between WN and WC (WN/WC) with an unseen OB-type companion."
  27. ^ Callingham et al. 2018, page 25, "Supplementary Information Table 3. Summary of the 0.2 and 10.0 keV observations of Apep. ObsID corresponds to the unique identification number assigned to each observation by the respective X-ray observatory.
  28. ^ Callingham et al. 2018, page 1, "Near-critical stellar rotation is known to drive such winds, suggesting this Wolf-Rayet system as a potential Galactic progenitor system to long-duration gamma-ray bursts."
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