Jump to content

Betelgeuse: Difference between revisions

Coordinates: Sky map 05h 55m 10.3053s, +07° 24′ 25.426″
From Wikipedia, the free encyclopedia
Browse history interactively
← Previous editNext edit →
Content deleted Content added
VisualWikitext
→Observation: surface magnetic field
Line 171: Line 171:
A series of [[spectropolarimetry|spectropolarimetric]] observations, obtained in 2010 with the [[Bernard Lyot Telescope]] at [[Pic du Midi Observatory]], revealed the presence of a weak magnetic field at the surface of Betelgeuse, suggesting that the giant convective motions of supergiant stars are able to trigger the onset of a small-scale [[dynamo]]. <ref name="A&A516">{{cite journal
A series of [[spectropolarimetry|spectropolarimetric]] observations, obtained in 2010 with the [[Bernard Lyot Telescope]] at [[Pic du Midi Observatory]], revealed the presence of a weak magnetic field at the surface of Betelgeuse, suggesting that the giant convective motions of supergiant stars are able to trigger the onset of a small-scale [[dynamo]]. <ref name="A&A516">{{cite journal
| author=M. Aurière, J.-F. Donati, R. Konstantinova Antova, G. Perrin, P. Petit, T. Roudier
| author=M. Aurière, J.-F. Donati, R. Konstantinova Antova, G. Perrin, P. Petit, T. Roudier
| title=The magnetic field of Betelgeuse : a local dynalo from giant convection cells ?
| title=The magnetic field of Betelgeuse : a local dynamo from giant convection cells ?
| journal=Astronomy & Astrophysics
| journal=Astronomy & Astrophysics
| year=2010 | volume=516 | pages=L2
| year=2010 | volume=516 | pages=L2

Revision as of 07:49, 5 July 2010

Template:Two other uses

Betelgeuse (α Ori)

The pink arrow at the star on left labeled α indicates Betelgeuse in Orion.
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Orion
Pronunciation /ˈbiːtəldʒuːz/ or
/ˈbɛtəldʒuːz/[1]
Right ascension 05h 55m 10.3053s[2]
Declination +07° 24′ 25.426″[2]
Apparent magnitude (V) 0.58[2] (0.3 to 1.2)
Characteristics
Spectral type M2Iab[2]
U−B color index 2.06[2]
B−V color index 1.77[2]
Variable type SR c[2] (Semi-regular)
Astrometry
Radial velocity (Rv)+21.0[2] km/s
Proper motion (μ) RA: 24.95 ± 0.08[3] mas/yr
Dec.: 9.56 ± 0.15[3] mas/yr
Parallax (π)5.07 ± 1.10 mas[3]
Distance640 ± 140 [3] ly
(197 ± 45 [3] pc)
Absolute magnitude (MV)−5.14
Details
Mass18-19[4] M☉
Radius936[5] R☉
Luminosity105,000[4] L☉
Surface gravity (log g)-0.5[6] cgs
Temperature3,500[6] K
Age~10 million[5] years
Other designations
Alpha Orionis, 58 Ori, HR 2061, BD+7°1055, HD 39801, SAO 113271, FK5 224, HIP 27989.[2]

Betelgeuse is a semiregular variable star located approximately 640 light-years from the Earth.[5] With an apparent magnitude ranging between 0.3 and 1.2, it is the ninth brightest star in the night sky. Although Betelgeuse has the Bayer designation Alpha Orionis (α Orionis / α Ori), it is most often the second brightest star in the constellation Orion behind α; Rigel (Beta Orionis) is usually brighter (Betelgeuse is a variable star and is on occasion brighter than Rigel). The star marks the upper right vertex of the Winter Triangle and center of the Winter Hexagon.

Betelgeuse is a red supergiant, and one of the largest and most luminous stars known. For comparison, if the star were at the center of our solar system its surface might extend out to between the orbits of Mars and Jupiter, wholly engulfing Mercury, Venus, the Earth and Mars. The angular diameter of Betelgeuse was first measured in 1920–1921 by Albert Abraham Michelson and Francis G. Pease using the 100 inch (2.5 m) John D. Hooker astronomical interferometer telescope atop Mount Wilson Observatory.

Astronomers believe Betelgeuse is only a few million years old, but has evolved rapidly because of its high mass.[7] Due to its age, Betelgeuse may be observed to supernova within the next millennium.

Etymology

Betelgeuse has been known variously as Betelgeux,[1] and Beteigeuze[8] in German (according to Bode[9][10]). Pronunciations for the star are as varied as its spellings. The Oxford English Dictionary has /ˈbɛtəldʒuːz/, /ˈbiːtəldʒuːz/, and French [ˈbɛtɛlʒœz]. The Royal Astronomical Society of Canada favors /ˈbɛtəldʒuːz/ BET-əl-jooz), while The Friendly Stars has /ˈbɛtəldʒəz/ BET-əl-jəz.[11] Webster's Collegiate Dictionary suggests /ˈbiːtəldʒuːs/, as in the film Beetlejuice and The Hitchhiker's Guide to the Galaxy,[11] or /ˈbɛtəldʒuːs/ with a final s sound, or either with a final z as in the OED.

Multiple sources with competing etymologies exist to describe the star's name. All agree that the last part of the name "-elgeuse" comes from the Arabic الجوزاء al-Jauzā', the indigenous Arabic name for the constellation Orion, a feminine name in old Arabian legend, and of uncertain meaning. Because جوز j-w-z, the root of jauzā', means "middle", al-Jauzā' roughly means "the Central One". Later, al-Jauzā' was also designated as the scientific Arabic name for Orion and for Gemini. The current Arabic name for Orion is الجبار al-Jabbār ("the Giant"), though the use of الجوزاء al-Jauzā' in the name of the star has continued.

One hypothesis is that the full name is a corruption of the Arabic يد الجوزاء Yad al-Jauzā' meaning "the Hand of al-Jauzā', i.e., Orion. European mistransliteration into Latin during the Middle Ages led to the first character y (ﻴ, with two dots underneath) being misread as a b (ﺒ, with only one dot underneath). During the Renaissance the star's name was written as بيت الجوزاء Bait al-Jauzā' ("house of Orion") or بط الجوزاء Baţ al-Jauzā', incorrectly thought to mean "armpit of Orion" (a true translation of "armpit" would be ابط, transliterated as Ibţ). This led to the modern rendering as Betelgeuse.[12]

A competing explanation came from Richard Hinckley Allen, who instead saw the origin in ابط الجوزاء Ibṭ al-Jauzah, which he claimed degenerated into a number of forms including Bed Elgueze, Beit Algueze, and Bet El-gueze.[13].

An alternative name for this star in Arabic was منكب الجوزاء Mankib al Jauzā' or "the Shoulder of Orion". In Persian, however, the name is اِبطالجوزا, derived from the Arabic ابط الجوزاء Ibţ al-Jauzā', "armpit of Orion".

Other Arabic names recorded include Al Yad al Yamnā ("the Right Hand"), Al Dhira ("the Arm"), and Al Mankib ("the Shoulder"), all appended to "of the giant".[13]

In traditional Chinese astronomy, Betelgeuse was known as 参宿四 (Shēnxiùsì, the Fourth (Star of the constellation) of Three (Stars)) as the constellation of 参宿 was at first a name only for the three stars in the girdle of Orion. Four stars were later added to this constellation, but the earlier name stuck.

In Japan, this star was called Heike-boshi (suggested by the red butterfly flag of the Heike clan), (平家星)[14][15], "the Star of the Heike clan" or Kin-waki, (金脇), "the Gold (Star) beside (Mitsu-boshi)."

Observation

Betelgeuse's variable brightness was first described in 1836 by Sir John Herschel, when he published his observations in Outlines of Astronomy, in which he noted an increase in activity from 1836–1840, followed by a subsequent reduction. In 1849, he noted a shorter cycle of variability which peaked in 1852. Later observers recorded unusually high maxima with an interval of several years, but only small variations from 1957—1967. The records of the American Association of Variable Star Observers show maximum brightnesses of magnitude 0.2 in 1933 and 1942, with minimums below magnitude 1.2 in 1927 and 1941.[16] This variability in brightness may explain why Johann Bayer designated it alpha as it may have rivalled the usually brighter Rigel (beta).[17]

File:Betelgeuse star (Hubble).jpg
Betelgeuse imaged in ultraviolet light by the Hubble Space Telescope and subsequently enhanced by NASA. The bright white spot is likely one of its poles. NASA/ESA credit.[18][19]
AAVSO V-band light curve of Betelgeuse (Alpha Orionis) from Dec. 1988 - Aug. 2002

In 1919, Albert Michelson and Francis Pease mounted a 6 metre (20 ft) interferometer on the front of the 2.5 metre (100 inch) telescope at Mount Wilson Observatory. Helped by John A. Anderson, in December 1920 Pease measured the angular diameter of α Orionis as 0.047 arcseconds. Given the then-current parallax value of 0.018 arcseconds, this resulted in an estimated radius of 3.84 × 108 km (240 million miles or 2.58 AU). However there was known uncertainty owing to limb darkening and measurement errors.[20][21] More recent visible-light observations of Betelgeuse have found the diameter to vary between 0.0568 and 0.0592 arcseconds.

In the late 1980s and early 1990s, Betelgeuse became a regular target for Aperture Masking Interferometry visible-light and infrared imaging, which revealed a number of bright spots on the star's surface, thought to result from convection.[22] These were the first optical and infrared images of the disk of a star other than our Sun, and generally showed one or more bright patches—indicating the location of hotspots in the star's photosphere. In 1995, the Hubble Space Telescope's Faint Object Camera captured an ultraviolet image of comparable resolution—this was the first conventional-telescope image (or "direct-image" in NASA terminology) of the disk of another star. The image was made at ultraviolet wavelengths as at ultraviolet wavelengths ground-based instruments cannot produce images with resolution as high as Hubble. Like earlier images, this ultraviolet image also contained a bright patch, indicating a hotter region by around 2000 kelvin, in this case on the southwestern portion of the star's surface.[23] Visual observations demonstrate that Betelgeuse's rotation axis has an inclination of about 20° to the direction of Earth, and a position (or height) angle of about 55°. The hot spot seen in the ultraviolet image is therefore hypothesized to be one of the star's poles.[24]

Recent ground-based infrared measurements of the disk of Betelgeuse gave a mid-infrared angular diameter of 54.7 ± 0.3 milli-arcseconds in November 1999, slightly smaller than the typical visible-light angular diameter. These measurements ignored any possible contribution from hotspots (which are less-noticeable in the mid-infrared) but factored-in some limb darkening, whereby the intensity of a star's image diminishes near the edge, as the photospheric gas gets thinner. It is difficult to define the precise diameter of Betelgeuse as the photosphere has no "edge"—instead the gas making up the photosphere gets gradually thinner with distance from the star.[25]

Image of the supergiant star Betelgeuse obtained with the NACO adaptive optics instrument on ESO’s Very Large Telescope.

Nobel Laureate Charles Townes announced evidence that 15 consecutive years of stellar contraction has been observed by UC Berkeley's Infrared Spatial Interferometer (ISI) atop Mt. Wilson Observatory in Southern California. Reported on June 9, 2009, the star has shrunk 15% since 1993 with an increasing rate. The average speed at which the radius of the star is shrinking over the last 15 years is around 210–219 m/s (470–490 mph).[citation needed] According to the university, Betelgeuse's diameter is about 5.5 A.U., and the star's radius has shrunk by a distance equal to half an astronomical unit, or about the orbit of Venus.[26][27]

In July 2009, images released by European Southern Observatory, taken by the ground based Very Large Telescope, gave a more detailed view of the surface of the star[28]. In the picture a plume of gas is seen extending from the star. This plume extends six times the diameter of Betelgeuse itself[29]. This is comparable to the distance between the Sun and Neptune.

A series of spectropolarimetric observations, obtained in 2010 with the Bernard Lyot Telescope at Pic du Midi Observatory, revealed the presence of a weak magnetic field at the surface of Betelgeuse, suggesting that the giant convective motions of supergiant stars are able to trigger the onset of a small-scale dynamo. [30]

Characteristics

Betelgeuse has most likely exhausted its supply of hydrogen and is currently generating energy by the thermonuclear fusion of helium into carbon and oxygen. On the Hertzsprung-Russell diagram, the star has moved off the main sequence and has swelled and cooled to become a red supergiant.

Because of the size and proximity of this star it has the third largest angular diameter as viewed from Earth,[31] being smaller than only the Sun and R Doradus. The angular size of Betelgeuse was one of the first to be measured with an astronomical interferometer and the apparent diameter was found to be variable. Between 1993 and 2009, the star's diameter has contracted by over 15 percent.[32] The precise diameter is hard to define since optical emissions decrease very gradually with radius from the center of Betelgeuse and the color of these emissions also vary with radius.

The distance to Betelgeuse is not known precisely. The measurement of the optical parallax from space yield a distance estimate of 495 light years, while parallax measurement using radio emission gives a longer estimate of 640 light years.[4] Assuming a compromise distance of 570 light years, the star's diameter would be about 950 to 1,000 times that of the Sun. If the Sun were the size of a beach ball, then Betelgeuse would be as large as a professional sports stadium. Although only 20 times more massive than the Sun,[4] this star could be hundreds of millions times greater in volume.

Betelgeuse has a color index (B-V) of 1.86. It was the first star on which starspots were resolved in optical images using a telescope, first from ground-based Aperture Masking Interferometry and later from the Hubble Space Telescope, followed by higher-resolution observations by the ground-based COAST telescope.[4][33] Betelgeuse's photosphere has an extended atmosphere which displays strong lines of emission, rather than absorption. This chromosphere has a temperature no higher than 5,500 K and may stretch outward to 7 times the diameter of the star. This extended gaseous atmosphere has been observed moving both away from and towards Betelgeuse, apparently depending on radial velocity fluctuations in the photosphere.[6]

Fate

The future fate of Betelgeuse depends on its mass; as it probably contains more than 15 solar masses, it will continue to burn and fuse elements until its core is iron, at which point Betelgeuse will explode as a type II supernova. During this event the core will collapse, leaving behind a neutron star remnant some 20 km in diameter.[17] However, if Betelgeuse is at the lighter end of estimated mass, it may instead contract to become a white dwarf.[17]

Considering its size and age of 8.5 million years, old for its size class, Betelgeuse may explode within the next thousand years.[34] At the current distance of Betelgeuse from the Earth, such a supernova explosion would be the brightest recorded; outshining the Moon in the night sky and becoming easily visible in broad daylight.[34] Professor J. Craig Wheeler of The University of Texas at Austin predicts the supernova will emit 1053 ergs of neutrinos, which will pass through the star's hydrogen envelope in around an hour, then reach the solar system several centuries later. Since its rotational axis is not pointed toward the Earth, Betelgeuse's supernova is unlikely to send a gamma ray burst in the direction of Earth large enough to damage Earth's ecosystems.[35] The flash of ultraviolet radiation from the explosion will be weaker than the ultraviolet output of the Sun.

The supernova would brighten to apparent magnitude –12 over a two week period, then remain at that intensity for two or three months before rapidly dimming. The year following the explosion, radioactive decay of cobalt to iron will dominate emission from the supernova remnant, and the resulting gamma rays will be blocked by the expanding envelope of hydrogen. If the neutron star remnant became a pulsar, then it might produce gamma rays for thousands of years.[36]

See also

References

  1. ^ a b Burchfield, R. W., (ed.). (1972) A Supplement to the Oxford English Dictionary, vol. 1・A-G, Claredon Press, Oxford, p.249.
  2. ^ a b c d e f g h i "SIMBAD query result: V* alf Ori -- Semi-regular pulsating Star". Centre de Données astronomiques de Strasbourg. Retrieved 2007-06-20.
  3. ^ a b c d e (5), Table 6, A New VLA-Hipparcos Distance to Betelgeuse and its Implications, Graham M. Harper, Alexander Brown, and Edward F. Guinan, The Astronomical Journal 135, #4 (April 2008), pp. 1430–1440, Bibcode:2008AJ....135.1430H, doi:10.1088/0004-6256/135/4/1430.
  4. ^ a b c d e astro.uiuc.edu, Betelgeuse (Alpha Orionis) - Update 2008, Stars, Jim Kaler, retrieved 9 October 2008.
  5. ^ a b c Professor James B. (Jim) Kaler. "Betelgeuse (Alpha Orionis)". University of Illinois. Retrieved 2009-07-19.
  6. ^ a b c Lobel, A.; Dupree, A. K. (2000). "Modeling the Variable Chromosphere of α Orionis". The Astrophysical Journal. 545: 454–74. doi:10.1086/317784. Retrieved 2007-02-04.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  7. ^ "Betelgeuse". SolStation. Retrieved 2005-11-11.
  8. ^ Likely the result of mistaking the l for an i. Ultimately, this led to the modern Betelgeuse.
  9. ^ Bode, J. E., (ed.). (1782) Vorstellung der Gestirne: auf XXXIV Kupfertafeln nach der Parisier Ausgabe des Flamsteadschen Himmelsatlas, Gottlieb August Lange, Berlin / Stralsund, pl. XXIV.
  10. ^ Bode, J. E., (ed.) (1801). Uranographia: sive Astrorum Descriptio, Fridericus de Harn, Berlin, pl. XII.
  11. ^ a b Jeff Kanipe (2005). "SpaceWatch -- A Star by Any Other Name". Retrieved 2009-10-23.
  12. ^ Kunitzsch, P., & Smart, T., (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, MA: Sky Pub. p. 45. ISBN 9781931559447.{{cite book}}: CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
  13. ^ a b c d e f Allen, R. H., (1963). Star Names: Their Lore and Meaning (rep. ed.). New York, NY: Dover Publications Inc. p. 310. ISBN 0486210790.{{cite book}}: CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
  14. ^ "Daijirin" p.2327 ISBN：4385139024
  15. ^ Hōei Nojiri"Shin seiza jyunrei"p.19 ISBN： 9784122041288
  16. ^ Burnham, Robert (1978). Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System, Volume 2. New York: Courier Dover Publications. p. 1290. ISBN 0486235688.
  17. ^ a b c Kaler, James B. (2002). The Hundred Greatest Stars. New York: Copernicus Books. p. 33. ISBN 0-387-95436-8.
  18. ^ The yellow/red "image" or "photo" of Betelgeuse usually seen is actually not a picture of the red giant but rather a mathematically generated image based on the photograph. The photograph was actually of much lower resolution: The entire Betelgeuse image fit entirely within a 10x10 pixel area on the Hubble Space Telescopes Faint Object Camera. The actual images were oversampled by a factor of 5 with bicubic spline interpolation, then deconvolved.
  19. ^ Gilliland, Ronald. "First Image of the Surface of a Star with the Hubble Space Telescope". Astrophysical Journal Letters v.463, p.L29. {{cite web}}: Italic or bold markup not allowed in: |publisher= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  20. ^ Michelson AA, Pease FG. (1921). "Measurement of the diameter of alpha Orionis with the interferometer". Astrophysical Journal. 53: 249–59. doi:10.1086/142603. Retrieved 2007-06-20.
  21. ^ Staff (2000). "Pease, Francis G (1881–1938)". Encyclopedia of Astronomy and Astrophysics. Retrieved 2007-06-20. {{cite web}}: Unknown parameter |month= ignored (help)
  22. ^ D. Buscher; et al. (1990). "Detection of a bright feature on the surface of Betelgeuse". Monthly Notices of the Royal Astronomical Society. 245: 7. Retrieved 2007-08-07. {{cite journal}}: Explicit use of et al. in: |author= (help) R. Wilson; et al. (1997). "The changing face of Betelgeuse". Monthly Notices of the Royal Astronomical Society. 291: 819. Retrieved 2007-08-07. {{cite journal}}: Explicit use of et al. in: |author= (help)
  23. ^ Petersen, Carolyn Collins; Brandt, John C. (1998) [1995]. Hubble Vision: Further Adeventures with the Hubble Space Telescope (2nd ed.). Cambridge, England: Cambridge University Press. pp. 91–92. ISBN 0-521-59291-7.{{cite book}}: CS1 maint: multiple names: authors list (link)
  24. ^ Uitenbroek H, Dupree AK, Gilliland RL (1998). "Spatially Resolved Hubble Space Telescope Spectra of the Chromosphere of α Orionis". The Astronomical Journal. 116: 2501–12. Retrieved 2007-06-20.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  25. ^ Weiner J; et al. (2000). "Precision Measurements of the Diameters of α Orionis and ο Ceti at 11 Microns". The Astrophysical Journal. 544 (2): 1097–1100. doi:10.1086/317264. Retrieved 2007-06-23. {{cite journal}}: Explicit use of et al. in: |author= (help)
  26. ^ Sanders, Robert (9 June 2009). "Red giant star Betelgeuse mysteriously shrinking". UCBerkeley News. UC Berkeley. Retrieved 18 April 2010.
  27. ^ "Red giant star Betelgeuse is mysteriously shrinking". e! Science News. 9 June 2009. Retrieved 18 April 2010.
  28. ^ http://www.eso.org/public/outreach/press-rel/pr-2009/pr-27-09.html
  29. ^ "The close circumstellar environment of Betelgeuse - Adaptive optics spectro-imaging in the near-IR with VLT/NACO". {{cite journal}}: Cite journal requires |journal= (help)
  30. ^ M. Aurière, J.-F. Donati, R. Konstantinova Antova, G. Perrin, P. Petit, T. Roudier (2010). "The magnetic field of Betelgeuse : a local dynamo from giant convection cells ?". Astronomy & Astrophysics. 516: L2. doi:10.1051/0004-6361/201014925. Retrieved 2010-07-04.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  31. ^ Bedding TR; et al. (1997). "The angular diameter of R Doradus: a nearby Mira-like star". Monthly Notices of the Royal Astronomical Society. 286 (4): 957–62. Retrieved 2007-06-20. {{cite journal}}: Explicit use of et al. in: |author= (help)
  32. ^ Ron Cowen (2009-06-10). "Betelgeuse shrinks: The red supergiant has lost 15 percent of its size". "The shrinkage corresponds to the star contracting by a distance equal to that between Venus and the sun, researchers reported June 9 at an American Astronomical Society meeting and in the June 1 Astrophysical Journal Letters."
  33. ^ Burns D; et al. (1997). "The surface structure and limb-darkening profile of Betelgeuse". Monthly Notices of the Royal Astronomical Society. 290 (1): L11–L16. Retrieved 2007-06-21. {{cite journal}}: Explicit use of et al. in: |author= (help)
  34. ^ a b "Sharpest views of Betelgeuse reveal how supergiant stars lose mass: Unveiling the true face of a behemoth". 29 July 2009. Retrieved 18 April 2010.
  35. ^ http://www.universetoday.com/guide-to-space/stars/betelgeuse/
  36. ^ Wheeler, J. Craig (2007). Cosmic Catastrophes: Exploding Stars, Black Holes, and Mapping the Universe (2nd ed.). Cambridge, UK: Cambridge University Press. pp. 115–17. ISBN 0-521-85714-7.

Further reading

Wikimedia Commons has media related to Betelgeuse.


Template:Link FA Template:Link FA

Retrieved from "https://en.wikipedia.org/enwiki/w/index.php?title=Betelgeuse&oldid=371813204"