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Sirius B

From EverybodyWiki Bios & Wiki

Sirius B

Hubble Space Telescope image of Sirius System, the dim star on the lower left is Sirius B
Observation data
Epoch J2000      Equinox J2000
Constellation Canis Major
Pronunciation /ˈsɪriəs/[1]
Right ascension  06h 45m 09.0s[2]
Declination −16° 43′ 06″[2]
Apparent magnitude (V) 8.44[3]
Characteristics
Evolutionary stage White dwarf
Spectral type DA2[3]
U−B colour index −1.04[4]
B−V colour index −0.03[4]
Astrometry
Radial velocity (Rv)−5.50[5] km/s
Proper motion (μ) RA: −461.571[6] mas/yr
Dec.: −914.520[6] mas/yr
Parallax (π)378.9 ± 1.4[7] mas
Distance8.61 ± 0.03 ly
(2.639 ± 0.010 pc)
Absolute magnitude (MV)+11.18[4]
Orbit[7]
Primaryα Canis Majoris A
Companionα Canis Majoris B
Period (P)50.1284±0.0043 yr
Semi-major axis (a)7.4957±0.0025"
(19.8 AU[lower-alpha 1])
Eccentricity (e)0.59142±0.00037
Inclination (i)136.336±0.040°
Longitude of the node (Ω)45.400±0.071°
Periastron epoch (T)1994.5715±0.0058
Argument of periastron (ω)
(secondary)		149.161±0.075°
Details
Mass1.018±0.011[7] M☉
Radius0.008098±0.6%[7] R☉
Radius5,634±34 km
Luminosity0.02448±1.3%[7] L☉
Surface gravity (log g)8.57[8] cgs
Temperature25,000±200[9] K
Age228+10
−8[7] Myr
Other designations
Dog Star, Aschere, Canicula, Al Shira, Sothis,[10] Alhabor,[11] Mrgavyadha, Lubdhaka,[12] Tenrōsei,[13] α Canis Majoris (α CMa), 9 Canis Majoris (9 CMa), HD 48915, HR 2491, BD−16°1591, GJ 244, LHS 219, ADS 5423, LTT 2638, HIP 32349[14]
Sirius B: EGGR 49, WD 0642-166, GCTP 1577.00[15]
Database references
SIMBADdata

Sirius B is a white dwarf, a remnant of an intermediate-mass star that have end its life, being the closest example to Earth. It is the secondary object of the Sirius binary system, of which the 'A' component is the brightest star in the night sky. Sirius B, on the other hand, can't be seen to the naked eye, as its luminosity is only 2% that of the Sun. Sirius is the fifth-nearest star system to the Sun, 8.6 light-years distant.

Like all white dwarfs, Sirius B is massive and dense: While its size is comparable to that of Earth, its mass is equivalent to that of the Sun. It is the progenitor of a 5 M☉ star that existed around 100 million years ago. Sirius B's current temperature is of 25,000 K (24,700 °C; 44,500 °F), 2.5 times hotter than Sirius A and over four times hotter than the Sun. It no longer produce energy via nuclear fusion, and its remaining heat will escape to space over time.

Artistic Representation of Sirius Star System

Due to its proximity, Sirius B has been the target of many studies in the last decades in attempt to discover extrasolar planets. None of them even detected a planet around Sirius B, though some planetary architethures still can't be ruled out by current observations.

Background

See also: White dwarf
File:Stellar Evolution (0.8-8 M☉).jpg
The evolution of intermediate-mass stars (0.8 to eight times the mass of the Sun.)

White dwarfs are remnants of intermediate-mass stars (such as the Sun) which have end their lifes.[16] Stars produce energy by the nuclear fusion of four hydrogen atoms in one helium atom. The energy released make the star in hydrostatic equilibrium. Eventually, in intermediate-mass stars, the core runs out of hydrogen, the outer layers start to expand and the star becomes a red giant, with dozens to hundreds of times its original size. The core shrinks in size under the star's weight, since it has less atoms. Then, pressure is enough to start nuclear fusion of hydrogen in a shell surrounding the core and, when there is sufficient pressure, helium fusion into carbon is achieved. In its last evolutionary stages, the star ejects its outer layers, and only a degenerate core is left.[17]

These astronomical objects do not produce energy via nuclear fusion and radiate their residual heat, cooling over time.[17] When virtually all heat has escaped, they become black dwarfs, which is expected to take over 10 trillion years, much more than the current age of the universe of 14 billion years. White dwarfs have an enormous density, from 100,000 to 100,000,000 grams per cubic centimeter,[18] so that a teaspoon of white dwarf matter would weigh 5.5 tonnes.[17] One of the smallest and most massive white dwarfs is in the HD 49798 system, which is 1.22 times more massive than the Sun,[19] yet has a radius of a mere 1,600 km, smaller than the Moon.[20] Other typical white dwarfs like Procyon B or van Maanen 2 have masses of 0.6 and 0.7 solar masses (M☉) and radii of about 0.011 and 0.012 solar radii (R☉), respectively.

Discovery and observations

The discovery of Sirius B dates from the mid 19th century. In a letter dated 10 August 1844, the German astronomer Friedrich Wilhelm Bessel found that the apparent motion of Sirius A varies, something never observed before. This was the first hint that Sirius has an unseen companion.[21] The faint companion, Sirius B, was first observed on 31 January 1862 by the American telescope-maker and astronomer Alvan Graham Clark.[22] This happened during testing of an 18.5-inch (470 mm) aperture great refractor telescope for Dearborn Observatory, which was one of the largest refracting telescope lenses in existence at the time, and the largest telescope in the United States.[23] Sirius B's sighting was confirmed on 8 March with smaller telescopes.[24]

In 1915, Walter Sydney Adams, using a 60-inch (1.5 m) reflector at Mount Wilson Observatory, observed the spectrum of Sirius B and determined that it was a faint whitish star.[25] This led astronomers to conclude that it was a white dwarf—the second to be discovered, after 40 Eridani B.[26] The diameter of Sirius A was first measured by Robert Hanbury Brown and Richard Q. Twiss in 1959 at Jodrell Bank using their stellar intensity interferometer.[27]

Due to the close presence of Sirius A, whose light outshine B, observations of Sirius B have been difficult in the XX century. In particular, measuring physical properties such as radius and temperature was extremely hard due to these interferences, while the mass could be relatively easily measured from the binary's orbit. In ultraviolet wavelengths, however, Sirius B is brighter than Sirius A, and with the development of ultraviolet satellites in the second half of the century such as the Extreme Ultraviolet Explorer (EUVE) and the International Ultraviolet Explorer (IUE), precise measurements of such properties were achieved. In 1998, astronomers combining spectroscopic measurements of the EUVE and IUE satellites derived a temperature of 25,000±35 K, together with a surface gravity of 108.51±0.04 cgs, precisions much higher than those of previous observations. A year before, the Hipparcos mission measured directly the system's distance from parallax, resulting in value of 2.637 ± 0.011 parsecs (8.601 ± 0.036 light-years), a 20% improvement toward previous measurements. Together with the ultraviolet data, this resulted in a radius of 0.0084±0.00025 R☉.[8]

File:Artist's impression of the sizes of Sirius B and the Earth.jpg
Artist's representing comparison between Sirius B and Earth

In 2005, using the Hubble Space Telescope, astronomers determined that Sirius B has nearly the diameter of the Earth, 12,000 kilometres (7,500 mi), with a mass 102% of the Sun's.[28]

Characteristics

Since Sirius B is in a binary star system, the mass can be measured using the orbital elements and Kepler's third law. The first measurement, back in 1910, resulted in an value of 0.94 M☉,[29] which is not so far from modern measurements, one from 2017 which combine multiple observations yield a value of 1.018±0.011 M☉.[30] The mass of Sirius B make it one of the most massive white dwarfs known, almost doubling the average of 0.6 M☉.[31]

The radius of Sirius B is 0.008098±1.6% times the Sun's radius,[30] equivalent to 5,635 km (3,501 mi) or 0.88 times Earth's radius (6,378 km). This is significantly smaller than other white dwarfs, such as Procyon B or van Maanen 2. White dwarfs, due to their structure, have the unusual property that how more massive it is, smaller it is, so a smaller white dwarf have more mass than a larger one.[32] The mass and radius can also be measured from its gravitational redshift, which results in values of 1.017 M☉ and 0.00803 R☉.[33]

As white dwarfs do not produce heat and cool over time, its age as a white dwarf can be estimated by calculating how long it took to cool to its current temperature, the so-called "cooling age". Sirius B has a mass of 1.02 M☉ and a temperature of 25,000 K or °C,[9] compared to the 5,772 K (5,499 °C) of the Sun[34] or 9,845 K (9,572 °C) of Sirius A.[35] From this method, an age of 126 million years is obtained. This is about half of the total age of the system of 230 million years.[30]

From theorethical calculations, the mass of the progenitor of Sirius B is calculated at 5.0±0.1 times the mass of the Sun,[30] and it is estimated to have been a B-type main-sequence star of class B5V.[36][37] The higher mass mean Sirius B used to be more luminous than Sirius A, so it burned the hydrogen at its core much faster. Higher mass in the system also mean the orbit used to be smaller – the periastron is predicted to have been between 1.5 to 1.6 AU. During the red giant phase, Sirius B expanded to a hundreds of times the size of the Sun, potentially transferring mass to Sirius A, albeit it never engulfed its companion.[30]

Sirius B is primarily composed of a carbon–oxygen mixture that was generated by helium fusion in the progenitor star.[9] This is overlaid by an envelope of lighter elements, with the materials segregated by mass because of the high surface gravity.[38] The outer atmosphere of Sirius B is now almost pure hydrogen—the element with the lowest mass—and no other elements are seen in its spectrum.[39]

Ancient observations of Sirius, dating back

Search for planets

Sirius B has been target of multiple surveys and studies in search for exoplanets orbiting it. Multiple exoplanets were found around white dwarfs, the first of such was PSR B1620−26 b.

Notes

  1. ↑ Semi-major axis in AU = semimajor axis in seconds/ parallax = 7.56″/0.37921 = 19.8 AU; as the eccentricity is 0.6, the distance fluctuates between 40% and 160% of that, roughly from 8 AU to 32 AU.

References

  1. ↑ "Sirius". Dictionary.com Unabridged (v 1.1). Random House, Inc. Retrieved 6 April 2008.
  2. ↑ 2.0 2.1 Gianninas, A.; Bergeron, P.; Ruiz, M.T. (2011). "A spectroscopic survey and analysis of bright, hydrogen-rich white dwarfs". The Astrophysical Journal. 743 (2): 138. arXiv:1109.3171. Bibcode:2011ApJ...743..138G. doi:10.1088/0004-637X/743/2/138. Unknown parameter |s2cid= ignored (help)
  3. ↑ 3.0 3.1 Holberg, J.B.; Oswalt, T.D.; Sion, E.M.; Barstow, M.A.; Burleigh, M.R. (2013). "Where are all the Sirius-like binary systems?". Monthly Notices of the Royal Astronomical Society. 435 (3): 2077–2091. arXiv:1307.8047. Bibcode:2013MNRAS.435.2077H. doi:10.1093/mnras/stt1433. Unknown parameter |s2cid= ignored (help)
  4. ↑ 4.0 4.1 4.2 McCook, G. P.; Sion, E. M. (2014). "Entry for WD 0642-166". VizieR Online Data Catalog. CDS. Bibcode:2016yCat....102035M. Search this book on
  5. ↑ Gontcharov, G.A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. ISSN 1063-7737. Unknown parameter |s2cid= ignored (help)
  6. ↑ Vallenari, A.; et al. (Gaia Collaboration) (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. arXiv:2208.00211. doi:10.1051/0004-6361/202243940. Gaia DR3 record for this source at VizieR.
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 Bond, Howard E.; Schaefer, Gail H.; Gilliland, Ronald L.; Holberg, Jay B.; Mason, Brian D.; Lindenblad, Irving W.; et al. (2017). "The Sirius system and its astrophysical puzzles: Hubble Space Telescope and ground-based astrometry". The Astrophysical Journal. 840 (2): 70. arXiv:1703.10625. Bibcode:2017ApJ...840...70B. doi:10.3847/1538-4357/aa6af8. Unknown parameter |s2cid= ignored (help)
  8. ↑ 8.0 8.1 Holberg, J. B.; Barstow, M. A.; Bruhweiler, F. C.; Cruise, A. M.; Penny, A. J. (April 1998). "Sirius B: A New, More Accurate View". The Astrophysical Journal. 497 (2): 935–942. Bibcode:1998ApJ...497..935H. doi:10.1086/305489. ISSN 0004-637X.
  9. ↑ 9.0 9.1 9.2 Liebert, James; Young, P. A.; Arnett, D.; Holberg, J. B.; Williams, K. A. (2005). "The age and progenitor mass of Sirius B". The Astrophysical Journal. 630 (1): L69. arXiv:astro-ph/0507523. Bibcode:2005ApJ...630L..69L. doi:10.1086/462419. Unknown parameter |s2cid= ignored (help)
  10. ↑ Hinckley, Richard Allen (1899). Star-names and Their Meanings. New York: G. E. Stechert. pp. 117–129. Search this book on
  11. ↑ Gingerich, Owen (1987-06). "Zoomorphic Astrolabes and the Introduction of Arabic Star Names into Europe". Annals of the New York Academy of Sciences. 500 (1): 89–104. doi:10.1111/j.1749-6632.1987.tb37197.x. ISSN 0077-8923. Check date values in: |date= (help)
  12. ↑ Singh, Nagendra Kumar (2002). Encyclopaedia of Hinduism, A Continuing Series. Anmol Publications PVT. LTD. p. 794. ISBN 81-7488-168-9. Search this book on
  13. ↑ Spahn, Mark; Hadamitzky, Wolfgang; Fujie-Winter, Kimiko (1996). The Kanji dictionary. Tuttle language library. Tuttle Publishing. p. 724. ISBN 0-8048-2058-9. Search this book on
  14. ↑ "Sirius A". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 20 October 2007.
  15. ↑ "Sirius B". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 23 October 2007.
  16. ↑ [email protected]. "White Dwarf". esahubble.org. Retrieved 2025-02-28.
  17. ↑ 17.0 17.1 17.2 "Stellar Evolution : The Life and Death of Our Luminous Neighbors". websites.umich.edu. Retrieved 2025-02-28.
  18. ↑ Fontaine, G.; Brassard, P.; Bergeron, P. (2001). "The potential of white dwarf cosmochronology". Publications of the Astronomical Society of the Pacific. 113 (782): 409–435. Bibcode:2001PASP..113..409F. doi:10.1086/319535.
  19. ↑ Rigoselli, Michela; De Grandis, Davide; Mereghetti, Sandro; Malacaria, Christian (30 May 2023). "Timing the X-ray pulsating companion of the hot subdwarf HD 49798 with NICER". Monthly Notices of the Royal Astronomical Society. 523 (2): 3043–3048. arXiv:2305.15845. doi:10.1093/mnras/stad1611.
  20. ↑ Mereghetti, S.; Pintore, F.; Rauch, T.; La Palombara, N.; Esposito, P.; Geier, S.; Pelisoli, I.; Rigoselli, M.; Schaffenroth, V.; Tiengo, A. (2021). "New X-ray observations of the hot subdwarf binary HD 49798/RX J0648.0–4418". Monthly Notices of the Royal Astronomical Society. 504: 920–925. arXiv:2104.03867. doi:10.1093/mnras/stab1004.
  21. ↑ Bessel, F. W. (December 1844). "On the Variations of the Proper Motions of Procyon and Sirius". Monthly Notices of the Royal Astronomical Society. 6 (11): 136–141. Bibcode:1844MNRAS...6R.136B. doi:10.1093/mnras/6.11.136a.
  22. ↑ Flammarion, Camille (August 1877). "The Companion of Sirius". The Astronomical Register. 15 (176): 186–189. Bibcode:1877AReg...15..186F.
  23. ↑ Craig, John; Gravatt, William; Slater, Thomas; Rennie, George. "The Craig Telescope". craig-telescope.co.uk. Retrieved 3 January 2011.
  24. ↑ Appletons' annual cyclopaedia and register of important events of the year: 1862. New York: D. Appleton & Company. 1863. p. 176. Search this book on
  25. ↑ Adams, W. S. (December 1915). "The Spectrum of the Companion of Sirius". Publications of the Astronomical Society of the Pacific. 27 (161): 236–237. Bibcode:1915PASP...27..236A. doi:10.1086/122440. Unknown parameter |s2cid= ignored (help)
  26. ↑ Holberg, J. B. (2005). "How Degenerate Stars Came to be Known as White Dwarfs". Bulletin of the American Astronomical Society. 37 (2): 1503. Bibcode:2005AAS...20720501H.
  27. ↑ Hanbury Brown, R.; Twiss, R. Q. (1958). "Interferometry of the Intensity Fluctuations in Light. IV. A Test of an Intensity Interferometer on Sirius A". Proceedings of the Royal Society of London. 248 (1253): 222–237. Bibcode:1958RSPSA.248..222B. doi:10.1098/rspa.1958.0240. Unknown parameter |s2cid= ignored (help)
  28. ↑ Barstow, M. A.; Bond, Howard E.; Holberg, J. B.; Burleigh, M. R.; Hubeny, I.; Koester, D. (2005). "Hubble Space Telescope spectroscopy of the Balmer lines in Sirius B". Monthly Notices of the Royal Astronomical Society. 362 (4): 1134–1142. arXiv:astro-ph/0506600. Bibcode:2005MNRAS.362.1134B. doi:10.1111/j.1365-2966.2005.09359.x. Unknown parameter |s2cid= ignored (help)
  29. ↑ Boss, L. (1910). Preliminary General Catalogue of 6188 stars for the epoch 1900. Carnegie Institution of Washington. Bibcode:1910pgcs.book.....B. LCCN 10009645 – via Archive.org. Search this book on
  30. ↑ 30.0 30.1 30.2 30.3 30.4 Bond, Howard E.; Schaefer, Gail H.; Gilliland, Ronald L.; Holberg, Jay B.; Mason, Brian D.; Lindenblad, Irving W.; et al. (2017). "The Sirius system and its astrophysical puzzles: Hubble Space Telescope and ground-based astrometry". The Astrophysical Journal. 840 (2): 70. arXiv:1703.10625. Bibcode:2017ApJ...840...70B. doi:10.3847/1538-4357/aa6af8. Unknown parameter |s2cid= ignored (help)
  31. ↑ Kepler, S.O.; Kleinman, S.J.; Nitta, A.; Koester, D.; Castanheira, B.G.; Giovannini, O.; Costa, A.F.M.; Althaus, L. (2007). "White dwarf mass distribution in the SDSS". Monthly Notices of the Royal Astronomical Society. 375 (4): 1315–1324. arXiv:astro-ph/0612277. Bibcode:2007MNRAS.375.1315K. doi:10.1111/j.1365-2966.2006.11388.x. Unknown parameter |s2cid= ignored (help)
  32. ↑ "Imagine the Universe!". imagine.gsfc.nasa.gov. Retrieved 2025-02-28.
  33. ↑ Joyce, S R G; Barstow, M A; Holberg, J B; Bond, H E; Casewell, S L; Burleigh, M R (2018-12-01). "The gravitational redshift of Sirius B". Monthly Notices of the Royal Astronomical Society. 481 (2): 2361–2370. doi:10.1093/mnras/sty2404. ISSN 0035-8711.
  34. ↑ "Sun Fact Sheet". nssdc.gsfc.nasa.gov. Retrieved 2025-02-28.
  35. ↑ Davis, J.; et al. (October 2010). "The Angular Diameter and Fundamental Parameters of Sirius A". Publications of the Astronomical Society of Australia. 28: 58–65. arXiv:1010.3790. doi:10.1071/AS10010.
  36. ↑ Siess, Lionel (2000). "Computation of Isochrones". Institut d'Astronomie et d'Astrophysique, Université libre de Bruxelles. Retrieved 24 March 2007.
  37. ↑ Palla, Francesco (16–20 May 2005). "Stellar evolution before the ZAMS". Proceedings of the international Astronomical Union 227. Italy: Cambridge University Press. pp. 196–205. Bibcode:1976IAUS...73...75P.
  38. ↑ Koester, D.; Chanmugam, G. (1990). "Physics of white dwarf stars". Reports on Progress in Physics. 53 (7): 837–915. Bibcode:1990RPPh...53..837K. doi:10.1088/0034-4885/53/7/001. Unknown parameter |s2cid= ignored (help)
  39. ↑ Holberg, J. B.; Barstow, M. A.; Burleigh, M. R.; Kruk, J. W.; Hubeny, I.; Koester, D. (2004). "FUSE observations of Sirius B". Bulletin of the American Astronomical Society. 36: 1514. Bibcode:2004AAS...20510303H.


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