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Tabby's Star

Coordinates: Sky map 20h 06m 15.457s, +44° 27′ 24.61″
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KIC 8462852

KIC 8462852 in infrared and ultraviolet
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Cygnus
Right ascension 20h 06m 15.457s
Declination +44° 27′ 24.61″
Apparent magnitude (V) +11.705±0.017
Characteristics
Evolutionary stage Main sequence[1]
Spectral type F3 V/IV
B−V color index 0.557
V−R color index 0.349
R−I color index 0.305
J−H color index 0.212
J−K color index 0.264
Astrometry
Distance1480 ly
(454 pc)
Absolute magnitude (MV)3.08[1][2]
Details
Mass1.43 M☉
Radius1.58 R☉
Luminosity (bolometric)4.7 L☉
Luminosity (visual, LV)5 L☉
Surface gravity (log g)4.0±0.2 cgs
Temperature6750±120 K
Metallicity0.0±0.1
Rotation0.8797±0.0001 days[1]
Rotational velocity (v sin i)84±4 km/s
Other designations
TYC 3162-665-1, 2MASS J20061546+4427248
Database references
SIMBADdata
KICdata

KIC 8462852[1] – eponymously Tabby's star (after lead author Tabetha S. Boyajian) or WTF star (formally for "Where's The Flux?",[3][4][5][6] but also a reference to an expression of disbelief[7]) – is an F-type main-sequence star located in the constellation Cygnus approximately 454 parsecs (1,480 ly) from Earth. Unusual light fluctuations of the star were discovered by citizen scientists as part of the Planet Hunters project, and in September 2015 astronomers and citizen scientists associated with the project posted a preprint of a paper on arXiv describing the data and possible interpretations.[1] The discovery was made from data collected by the Kepler space telescope,[1][8] which observes changes in the brightness of distant stars in order to detect exoplanets.[9]

The star's large irregular changes in brightness are consistent with many small masses together orbiting the star in "tight formation".[8] Several hypotheses have been proposed to explain the star's highly unusual light curve, most notably that it could be signs of activity associated with intelligent extraterrestrial life.[8][10][11][12] The SETI Institute's initial radio reconnaissance of the star, however, indicated "no evidence for persistent technology-related signals in the microwave frequency range..."[13]

Apparent location

Map showing location of NGC 6866. KIC 8462852 is northeast between NGC 6866 and ο¹ Cygni.

KIC 8462852 in Cygnus[14] is located roughly halfway between the major visually apparent bright stars Deneb (α Cyg, α Cygni, Alpha Cygni) and Rukh (δ Cyg, δ Cygni, Delta Cygni) to the eye as part of the Northern Cross.[15] KIC 8462852 is situated south of Omicron¹ Cygni (ο¹ Cygni, 31 Cygni), and northeast of the star cluster NGC 6866.[15] While only a few arcminutes away from the cluster, it is unrelated and closer to the Sun than it is to the star cluster. With an apparent magnitude of 11.7, the star cannot be seen by the naked eye, but is visible with a 5-inch (130 mm) telescope[16] in a dark sky with little light pollution.

Observed Kepler data

Observations of the luminosity of the star by the Kepler space telescope show small, frequent, non-periodic dips in brightness, along with two large recorded dips in brightness appearing to occur roughly 750 days apart. The amplitude of the changes in the star's brightness, and the aperiodicity of the changes, mean that this star is of particular interest for astronomers.[12] The star's changes in brightness are consistent with many small masses orbiting the star in "tight formation".[8]

The first major dip, on 5 March 2011, obscured the star's brightness by up to 15%, and the other (on 28 February 2013) by up to 22%. In comparison, a planet the size of Jupiter would only obscure a star of this size by 1%, indicating that whatever is blocking light during the star's major dips is not a planet, but rather something covering up to half the width of the star.[12] Due to the failure of two of Kepler's reaction wheels, the star's predicted 750-day dip around April 2015 was not recorded;[1][11] further observations are planned for May 2017.[11]

Hypotheses

Based on the star's spectral and star type, the star's changes in brightness could not be attributed to intrinsic variability,[1] so a few hypotheses have been proposed involving material orbiting the star and blocking its light, but none of these fully explain the observed data.

One explanation for the star's odd reduction in light is that it is due to a cloud of disintegrating comets orbiting the star elliptically.[1][17] Under this scenario, gravity from a nearby star may have caused comets from the star's Oort cloud to fall in towards the star. Evidence to support this hypothesis includes the fact that a red dwarf exists 132 billion kilometers (885 AU) away from KIC 8462852. However, the notion that disturbed Oort cloud comets orbiting elliptically close to the star could exist in high enough numbers to obscure 22% of the star's observed luminosity has been doubted.[12]

Other proposed explanations involve instrument/data artifacts, variable B(e) star, interstellar dust, a series of giant planets with very large ring structures,[18][19] and a recently captured asteroid field.[1]

High resolution spectroscopy and imaging observations have also been made, as well as spectral energy distribution analyses using the Nordic Optical Telescope in Spain.[1][18] A massive collision scenario would create warm dust that glows in infrared wavelengths, but there is no observed excess infrared energy, ruling out massive planetary collision debris.[12] Other researchers think the planetary debris field explanation is unlikely, given there is a very low probability that Kepler would ever witness such an event on account of the rarity of collisions of that size.[1]

Astronomer Jason Wright (who was consulted by Boyajian)[6][20] and others who have studied KIC 8462852 have suggested in a follow-up paper that if the star is younger than its position and speed would suggest, then it may still have coalescing material around it.[3] In addition they hypothesized that the objects eclipsing the star could be parts of a megastructure made by an alien civilization, such as a Dyson swarm,[3][8][17][21][22][23] a hypothetical structure that an advanced civilization might build around a star to intercept some of its light for their energy needs.[24][25][26] KIC 8462852 has, regarding extensive media speculation on this matter, had comparison drawn by Steve Howell of the Kepler telescope's planet hunting project with KIC 4110611, another star with an odd light curve (which proved, after years of research, to be a part of a five-star system),[27] and Wright has emphasized the importance of upcoming spectral studies regarding the current light curve data.[28] According to Wright, the likelihood of extraterrestrial intelligence being the cause of the dimming is very low, however the star is an outstanding SETI target because natural explanations have yet to fully explain the dimming phenomenon.[3][21]

Followup studies

On 19 October 2015, the SETI Institute announced that it had begun using the Allen Telescope Array to look for radio emissions from possible intelligent extraterrestrial life in the vicinity of the star.[29][30] After a two-week survey SETI reported no evidence of technology-related radio signals from that direction.[13][31]

Many optical telescopes are monitoring KIC 8462852 in anticipation of another multi-day dimming event, with planned follow-up observations of a dimming event using large telescopes equipped with spectrographs to determine if the eclipsing mass is a solid object, or is comprised of dust or gas.[32]

Additional follow-up observations potentially include using the ground-based Green Bank Telescope, the Very Large Array Radio Telescope,[18][33] and future orbital telescopes dedicated to exoplanetology such as WFIRST, TESS, and PLATO.[21][26]

See also

  • PSR B1919+21, a star mistaken for an alien radio signal (LGM-1)

References

  1. ^ a b c d e f g h i j k l Boyajian, T. S.; LaCourse, D. M.; Rappaport, S. A.; Fabrycky, D.; Fischer, D. A.; et al. (11 September 2015). "Planet Hunters X. KIC 8462852 - Where's the Flux?". arXiv:1509.03622 [astro-ph.SR]. Submitted to Monthly Notices of the Royal Astronomical Society.
  2. ^ Pecaut, Mark J.; Mamajek, Eric E. (September 2013). "Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-main-sequence Stars". The Astrophysical Journal Supplement. 208 (1). 9. arXiv:1307.2657. Bibcode:2013ApJS..208....9P. doi:10.1088/0067-0049/208/1/9.
  3. ^ a b c d Wright, Jason (15 October 2015). "KIC 8462852: Where's the Flux?". AstroWright. Pennsylvania State University. Retrieved 16 October 2015.
  4. ^ Newsome, John (16 October 2015). "Space anomaly gets extraterrestrial intelligence experts' attention". CNN News. Retrieved 16 October 2015.
  5. ^ "Discovery of a strange star could mean alien life". Fox News. 15 October 2015. Retrieved 16 October 2015.
  6. ^ a b King, Bob (16 October 2015). "What's Orbiting KIC 8462852 – Shattered Comet or Alien Megastructure?". Universe Today. Retrieved 16 October 2015.
  7. ^ Marcus Strom (15 October 2015), It's either aliens or a swarm of comets: scientists baffled by WTF 001, our galaxy's strangest star, The Sydney Morning Herald
  8. ^ a b c d e Andersen, Ross (13 October 2015). "The Most Mysterious Star in Our Galaxy". The Atlantic. Retrieved 13 October 2015.
  9. ^ Grush, Loren (16 October 2015). "Why it's so hard for astronomers to discuss the possibility of alien life". The Verge. Retrieved 17 October 2015.
  10. ^ Kaplan, Sarah (15 October 2015). "The strange star that has serious scientists talking about an alien megastructure". The Washington Post. Retrieved 15 October 2015.
  11. ^ a b c Aron, Jacob (18 September 2015). "Citizen scientists catch cloud of comets orbiting distant star". New Scientist. Retrieved 15 October 2015.
  12. ^ a b c d e Plait, Phil (14 October 2015). "Did Astronomers Find Evidence of an Alien Civilization? (Probably Not. But Still Cool.)". Slate. Retrieved 15 October 2015.
  13. ^ a b "Looking For Deliberate Radio Signals From KIC 8462852". 5 November 2015. Retrieved 5 November 2015.
  14. ^ "KIC10 Search Results". Space Telescope Science Institute. Retrieved 16 October 2015.
  15. ^ a b Sinnott, Roger W. (2010). Sky & Telescope's Pocket Sky Atlas (3rd ed.). Cambridge, Massachusetts: Sky Publishing. ISBN 978-1-931559-31-7.
  16. ^ Masi, Gianluca (16 October 2015). "KIC 8462852: A star and its secrets". The Virtual Telescope Project 2.0. Retrieved 22 October 2015.
  17. ^ a b Fecht, Sarah (13 October 2015). "Have We Detected Megastructures Built By Aliens Around A Distant Star? Or Just A Cloud Of Comets? Scientists Want To Investigate Further". Popular Science. Retrieved 14 October 2015.
  18. ^ a b c Rzetelny, Xaq (16 October 2015). "Something—we're not sure what—is radically dimming a star's light". Ars Technica. Retrieved 17 October 2015.
  19. ^ Siegel, Ethan (16 October 2015). "No, Astronomers Probably Haven't Found 'Alien Megastructures'". Forbes. Retrieved 17 October 2015.
  20. ^ Laker, Chris (16 October 2015). "'Alien megastructure' may explain light patterns from 'bizarre' star, say scientists". BT.com. Retrieved 17 October 2015.
  21. ^ a b c Wright, Jason T.; Cartier, Kimberly M. S.; Zhao, Ming; Jontof-Hutter, Daniel; Ford, Eric B. (15 October 2015). "The Ĝ Search for Extraterrestrial Civilizations with Large Energy Supplies. IV. The Signatures and Information Content of Transiting Megastructures". arXiv:1510.04606 [astro-ph.EP]. Submitted to The Astrophysical Journal.
  22. ^ "Good night, sleep tight: Advanced alien civilisations rare or absent in the local Universe" (Press release). ASTRON. 15 September 2015. Retrieved 15 October 2015.
  23. ^ Williams, Lee (15 October 2015). "Astronomers may have found giant alien 'megastructures' orbiting star near the Milky Way". The Independent. Retrieved 15 October 2015.
  24. ^ Jones, Morris (November–December 2015). "Reconsidering macro-artefacts in SETI searches". Acta Astronautica. 116: 161–165. doi:10.1016/j.actaastro.2015.07.011.
  25. ^ O'Neill, Ian (14 October 2015). "Has Kepler Discovered an Alien Megastructure?". Discovery.com. Retrieved 17 October 2015.
  26. ^ a b Siemion, Andrew (29 September 2015). "Prepared Statement by Andrew Siemion - Hearing on Astrobiology". House Committee on Science, Space, and Technology. SpaceRef.com. Retrieved 19 October 2015.
  27. ^ "Mysterious star stirs controversy in astronomy world". The Express Tribune. Agence France-Presse. 20 October 2015.
  28. ^ Orwig, Jessica (15 October 2015). "We spoke with some of the astronomers who discovered the 'alien' megastructure to find out if it's fact or fiction". Business Insider.
  29. ^ Wall, Mike (19 October 2015). "Search For Intelligent Aliens Near Bizarre Dimming Star Has Begun". Space.com. Retrieved 20 October 2015.
  30. ^ Orwig, Jessica (23 October 2015). "Scientists are days from finding out if that mysterious star could actually harbor aliens". Business Insider.
  31. ^ Harp, G. R.; Richards, Jon; Shostak, Seth; Tarter, J. C.; Vakoch, Douglas A.; Munson, Chris (5 November 2015). "Radio SETI Observations of the Anomalous Star KIC 8462852" (PDF). arXiv Repository. Retrieved 6 November 2015.
  32. ^ Wall, Mike (28 October 2015). "'Alien Megastructure' Mystery May Soon Be Solved". Space.com. Retrieved 28 October 2015.
  33. ^ Mack, Eric (17 October 2015). "The story behind 'alien megastructures' scientists may have found (but probably didn't)". CNET. Retrieved 19 October 2015.
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