Source: https://gravity.wikia.org/wiki/White_dwarf
Timestamp: 2019-04-22 18:13:43+00:00

Document:
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored thermal energy. White dwarfs comprise roughly 6% of all known stars in the solar neighborhood. The unusual faintness of white dwarfs was first recognized in 1910 by Henry Norris Russell, Edward Charles Pickering, and Williamina Fleming;, p. 1 the name white dwarf was coined by Willem Luyten in 1922.
White dwarfs are thought to be the final evolutionary state of all stars whose mass is not too high—over 97% of the stars in our galaxy., §1. After the hydrogen–fusing lifetime of a main-sequence star of low or medium mass ends, it will expand to a red giant which fuses helium to carbon and oxygen in its core by the triple-alpha process. If a red giant has insufficient mass to generate the core temperatures required to fuse carbon, an inert mass of carbon and oxygen will build up at its center. After shedding its outer layers to form a planetary nebula, it will leave behind this core, which forms the remnant white dwarf. Usually, therefore, white dwarfs are composed of carbon and oxygen. It is also possible that core temperatures suffice to fuse carbon but not neon, in which case an oxygen-neon–magnesium white dwarf may be formed. Also, some helium white dwarfs appear to have been formed by mass loss in binary systems.
A white dwarf is very hot when it is formed but since it has no source of energy, it will gradually radiate away its energy and cool down. This means that its radiation, which initially has a high color temperature, will lessen and redden with time. Over a very long time, a white dwarf will cool to temperatures at which it will no longer be visible, and become a cold black dwarf. However, since no white dwarf can be older than the age of the Universe (approximately 13.7 billion years), even the oldest white dwarfs still radiate at temperatures of a few thousand kelvins, and no black dwarfs are thought to exist yet.
Template:Star nav Although white dwarfs are known with estimated masses as low as 0.17 and as high as 1.33 solar masses, the mass distribution is strongly peaked at 0.6 solar mass, and the majority lie between 0.5 to 0.7 solar mass. The estimated radii of observed white dwarfs, however, are typically between 0.008 and 0.02 times the radius of the Sun; this is comparable to the Earth's radius of approximately 0.009 solar radius. A white dwarf, then, packs mass comparable to the Sun's into a volume that is typically a million times smaller than the Sun's; the average density of matter in a white dwarf must therefore be, very roughly, 1,000,000 times greater than the average density of the Sun, or approximately 106 grams (1 tonne) per cubic centimeter. White dwarfs are composed of one of the densest forms of matter known, surpassed only by other compact stars such as neutron stars, black holes and, hypothetically, quark stars.
The existence of a limiting mass that no white dwarf can exceed is another consequence of being supported by electron degeneracy pressure. These masses were first published in 1929 by Wilhelm Anderson and in 1930 by Edmund C. Stoner. The modern value of the limit was first published in 1931 by Subrahmanyan Chandrasekhar in his paper "The Maximum Mass of Ideal White Dwarfs". For a nonrotating white dwarf, it is equal to approximately 5.7/μe2 solar masses, where μe is the average molecular weight per electron of the star., eq. (63) As the carbon-12 and oxygen-16 which predominantly compose a carbon-oxygen white dwarf both have atomic number equal to half their atomic weight, one should take μe equal to 2 for such a star, leading to the commonly quoted value of 1.4 solar masses. (Near the beginning of the 20th century, there was reason to believe that stars were composed chiefly of heavy elements,, p. 955 so, in his 1931 paper, Chandrasekhar set the average molecular weight per electron, μe, equal to 2.5, giving a limit of 0.91 solar mass.) Together with William Alfred Fowler, Chandrasekhar received the Nobel prize for this and other work in 1983. The limiting mass is now called the Chandrasekhar limit.
If a white dwarf were to exceed the Chandrasekhar limit, and nuclear reactions did not take place, the pressure exerted by electrons would no longer be able to balance the force of gravity, and it would collapse into a denser object such as a neutron star. However, carbon-oxygen white dwarfs accreting mass from a neighboring star undergo a runaway nuclear fusion reaction, which leads to a Type Ia supernova explosion in which the white dwarf is destroyed, just before reaching the limiting mass.
White dwarfs have low luminosity and therefore occupy a strip at the bottom of the Hertzsprung-Russell diagram, a graph of stellar luminosity versus color (or temperature). They should not be confused with low-luminosity objects at the low-mass end of the main sequence, such as the hydrogen-fusing red dwarfs, whose cores are supported in part by thermal pressure, or the even lower-temperature brown dwarfs.
The visible radiation emitted by white dwarfs varies over a wide color range, from the blue-white color of an O-type main sequence star to the red of a M-type red dwarf. White dwarf effective surface temperatures extend from over 150,000 K to under 4,000 K. In accordance with the Stefan-Boltzmann law, luminosity increases with increasing surface temperature; this surface temperature range corresponds to a luminosity from over 100 times the Sun's to under 1/10,000th that of the Sun's. Hot white dwarfs, with surface temperatures in excess of 30,000 K, have been observed to be sources of soft (i.e., lower-energy) X-rays. This enables the composition and structure of their atmospheres to be studied by soft X-ray and extreme ultraviolet observations.
As was explained by Leon Mestel in 1952, unless the white dwarf accretes matter from a companion star or other source, its radiation comes from its stored heat, which is not replenished., §2.1. White dwarfs have an extremely small surface area to radiate this heat from, so they cool gradually, remaining hot for a long time. As a white dwarf cools, its surface temperature decreases, the radiation which it emits reddens, and its luminosity decreases. Since the white dwarf has no energy sink other than radiation, it follows that its cooling slows with time. Bergeron, Ruiz, and Leggett, for example, estimate that after a carbon white dwarf of 0.59 solar mass with a hydrogen atmosphere has cooled to a surface temperature of 7,140 K, taking approximately 1.5 billion years, cooling approximately 500 more kelvins to 6,590 K takes around 0.3 billion years, but the next two steps of around 500 kelvins (to 6,030 K and 5,550 K) take first 0.4 and then 1.1 billion years., Table 2. Although white dwarf material is initially plasma—a fluid composed of nuclei and electrons—it was theoretically predicted in the 1960s that at a late stage of cooling, it should crystallize, starting at the center of the star. The crystal structure is thought to be a body-centered cubic lattice. In 1995 it was pointed out that asteroseismological observations of pulsating white dwarfs yielded a potential test of the crystallization theory, and in 2004, Travis Metcalfe and a team of researchers at the Harvard-Smithsonian Center for Astrophysics estimated, on the basis of such observations, that approximately 90% of the mass of BPM 37093 had crystallized. Other work gives a crystallized mass fraction of between 32% and 82%.
White dwarfs whose primary spectral classification is DA have hydrogen-dominated atmospheres. They make up the majority (approximately three-quarters) of all observed white dwarfs. A small fraction (roughly 0.1%) have carbon-dominated atmospheres, the hot (above 15,000 K) DQ class. The classifiable remainder (DB, DC, DO, DZ, and cool DQ) have helium-dominated atmospheres. Assuming that carbon and metals are not present, which spectral classification is seen depends on the effective temperature. Between approximately 100,000 K to 45,000 K, the spectrum will be classified DO, dominated by singly ionized helium. From 30,000 K to 12,000 K, the spectrum will be DB, showing neutral helium lines, and below about 12,000 K, the spectrum will be featureless and classified DC.,§ 2.4 The reason for the absence of white dwarfs with helium-dominated atmospheres and effective temperatures between 30,000 K and 45,000 K, called the DB gap, is not clear. It is suspected to be due to competing atmospheric evolutionary processes, such as gravitational separation and convective mixing.
If the mass of a main-sequence star is lower than approximately half a solar mass, it will never become hot enough to fuse helium at its core. It is thought that, over a lifespan exceeding the age (~13.7 billion years) of the Universe, such a star will eventually burn all its hydrogen and end its evolution as a helium white dwarf composed chiefly of helium-4 nuclei. Owing to the time this process takes, it is not thought to be the origin of observed helium white dwarfs. Rather, they are thought to be the product of mass loss in binary systems  or mass loss due to a large planetary companion.
If a star is massive enough, its core will eventually become sufficiently hot to fuse carbon to neon, and then to fuse neon to iron. Such a star will not become a white dwarf, because the mass of its central, non-fusing core, supported by electron degeneracy pressure, will eventually exceed the largest possible mass supportable by degeneracy pressure. At this point the core of the star will collapse and it will explode in a core-collapse supernova which will leave behind a remnant neutron star, black hole, or possibly a more exotic form of compact star. Some main-sequence stars, of perhaps 8 to 10 solar masses, although sufficiently massive to fuse carbon to neon and magnesium, may be insufficiently massive to fuse neon. Such a star may leave a remnant white dwarf composed chiefly of oxygen, neon, and magnesium, provided that its core does not collapse, and provided that fusion does not proceed so violently as to blow apart the star in a supernova. Although some isolated white dwarfs have been identified which may be of this type, most evidence for the existence of such stars comes from the novae called ONeMg or neon novae. The spectra of these novae exhibit abundances of neon, magnesium, and other intermediate-mass elements which appear to be only explicable by the accretion of material onto an oxygen-neon-magnesium white dwarf.
A white dwarf is stable once formed and will continue to cool almost indefinitely; eventually, it will become a black white dwarf, also called a black dwarf. Assuming that the Universe continues to expand, it is thought that in 1019 to 1020 years, the galaxies will evaporate as their stars escape into intergalactic space., §IIIA. White dwarfs should generally survive this, although an occasional collision between white dwarfs may produce a new fusing star or a super-Chandrasekhar mass white dwarf which will explode in a type Ia supernova., §IIIC, IV. The subsequent lifetime of white dwarfs is thought to be on the order of the lifetime of the proton, known to be at least 1032 years. Some simple grand unified theories predict a proton lifetime of no more than 1049 years. If these theories are not valid, the proton may decay by more complicated nuclear processes, or by quantum gravitational processes involving a virtual black hole; in these cases, the lifetime is estimated to be no more than 10200 years. If protons do decay, the mass of a white dwarf will decrease very slowly with time as its nuclei decay, until it loses enough mass to become a nondegenerate lump of matter, and finally disappears completely., §IV.
A white dwarf's stellar and planetary system is inherited from its progenitor star and may interact with the white dwarf in various ways. Infrared spectroscopic observations made by NASA's Spitzer Space Telescope of the central star of the Helix Nebula suggest the presence of a dust cloud, which may be caused by cometary collisions. It is possible that infalling material from this may cause X-ray emission from the central star. Similarly, observations made in 2004 indicated the presence of a dust cloud around the young white dwarf star G29-38 (estimated to have formed from its AGB progenitor about 500 million years ago), which may have been created by tidal disruption of a comet passing close to the white dwarf. If a white dwarf is in a binary system with a stellar companion, a variety of phenomena may occur, including novae and Type Ia supernovae. It may also be a super-soft x-ray source if it is able to take material from its companion fast enough to sustain fusion on its surface.
Composite image of SN 1572 or Tycho's Nova, the remnant of a Type Ia supernova.
Accretion provides the currently favored mechanism, the single-degenerate model, for type Ia supernovae. In this model, a carbon–oxygen white dwarf accretes material from a companion star,, p. 14. increasing its mass and compressing its core. It is believed that compressional heating of the core leads to ignition of carbon fusion as the mass approaches the Chandrasekhar limit. Because the white dwarf is supported against gravity by quantum degeneracy pressure instead of by thermal pressure, adding heat to the star's interior increases its temperature but not its pressure, so the white dwarf does not expand and cool in response. Rather, the increased temperature accelerates the rate of the fusion reaction, in a runaway process that feeds on itself. The thermonuclear flame consumes much of the white dwarf in a few seconds, causing a type Ia supernova explosion that obliterates the star. In another possible mechanism for type Ia supernovae, the double-degenerate model, two carbon-oxygen white dwarfs in a binary system merge, creating an object with mass greater than the Chandrasekhar limit in which carbon fusion is then ignited., p. 14.
Before accretion of material pushes a white dwarf close to the Chandrasekhar limit, accreted hydrogen-rich material on the surface may ignite in a less destructive type of thermonuclear explosion powered by hydrogen fusion. Since the white dwarf's core remains intact, these surface explosions can be repeated as long as accretion continues. This weaker kind of repetitive cataclysmic phenomenon is called a (classical) nova. Astronomers have also observed dwarf novae, which have smaller, more frequent luminosity peaks than classical novae. These are thought to be caused by the release of gravitational potential energy when part of the accretion disc collapses onto the star, rather than by fusion. In general, binary systems with a white dwarf accreting matter from a stellar companion are called cataclysmic variables. As well as novae and dwarf novae, several other classes of these variables are known. Both fusion- and accretion-powered cataclysmic variables have been observed to be X-ray sources.
↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Extreme Stars: White Dwarfs & Neutron Stars, Jennifer Johnson, lecture notes, Astronomy 162, Ohio State University. Accessed on line May 3, 2007.
↑ The One Hundred Nearest Star Systems, Todd J. Henry, RECONS, April 11, 2007. Accessed on line May 4, 2007.
↑ 3.0 3.1 3.2 3.3 White Dwarfs, E. Schatzman, Amsterdam: North-Holland, 1958.
↑ 4.0 4.1 4.2 4.3 How Degenerate Stars Came to be Known as White Dwarfs, J. B. Holberg, Bulletin of the American Astronomical Society 37 (December 2005), p. 1503.
↑ 5.0 5.1 5.2 5.3 The Potential of White Dwarf Cosmochronology, G. Fontaine, P. Brassard, and P. Bergeron, Publications of the Astronomical Society of the Pacific 113, #782 (April 2001), pp. 409–435.
↑ 6.0 6.1 6.2 6.3 6.4 Late stages of evolution for low-mass stars, Michael Richmond, lecture notes, Physics 230, Rochester Institute of Technology. Accessed on line May 3, 2007.
↑ 7.0 7.1 On Possible Oxygen/Neon White Dwarfs: H1504+65 and the White Dwarf Donors in Ultracompact X-ray Binaries, K. Werner, N. J. Hammer, T. Nagel, T. Rauch, and S. Dreizler, pp. 165 ff. in 14th European Workshop on White Dwarfs; Proceedings of a meeting held at Kiel, July 19–23, 2004, edited by D. Koester and S. Moehler, San Francisco: Astronomical Society of the Pacific, 2005.
↑ 8.0 8.1 A Helium White Dwarf of Extremely Low Mass, James Liebert, P. Bergeron, Daniel Eisenstein, H.C. Harris, S.J. Kleinman, Atsuko Nitta, and Jurek Krzesinski, The Astrophysical Journal 606, #2 (May 2004), pp. L147–L149. Accessed on line March 5, 2007.
↑ 9.0 9.1 Cosmic weight loss: The lowest mass white dwarf, press release, Harvard-Smithsonian Center for Astrophysics, April 17, 2007.
↑ 10.0 10.1 Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology, D. N. Spergel, R. Bean, O. Doré, M. R. Nolta, C. L. Bennett, J. Dunkley, G. Hinshaw, N. Jarosik, E. Komatsu, L. Page, H. V. Peiris, L. Verde, M. Halpern, R. S. Hill, A. Kogut, M. Limon, S. S. Meyer, N. Odegard, G. S. Tucker, J. L. Weiland, E. Wollack, and E. L. Wright, arXiv:astro-ph/0603449v2, February 27, 2007.
↑ The orbit and the masses of 40 Eridani BC, W. H. van den Bos, Bulletin of the Astronomical Institutes of the Netherlands 3, #98 (July 8, 1926), pp. 128–132.
↑ Astrometric study of four visual binaries, W. D. Heintz, Astronomical Journal 79, #7 (July 1974), pp. 819–825.
↑ 15.0 15.1 On the Variations of the Proper Motions of Procyon and Sirius, F. W. Bessel, communicated by J. F. W. Herschel, Monthly Notices of the Royal Astronomical Society 6 (December 1844), pp. 136–141.
↑ 16.0 16.1 The Companion of Sirius, Camille Flammarion, The Astronomical Register 15, #176 (August 1877), pp. 186–189.
↑ The Spectrum of the Companion of Sirius, W. S. Adams, Publications of the Astronomical Society of the Pacific 27, #161 (December 1915), pp. 236–237.
↑ Two Faint Stars with Large Proper Motion, A. van Maanen, Publications of the Astronomical Society of the Pacific 29, #172 (December 1917), pp. 258–259.
↑ The Mean Parallax of Early-Type Stars of Determined Proper Motion and Apparent Magnitude, Willem J. Luyten, Publications of the Astronomical Society of the Pacific 34, #199 (June 1922), pp. 156–160.
↑ Third Note on Faint Early Type Stars with Large Proper Motion, Willem J. Luyten, Publications of the Astronomical Society of the Pacific 34, #202 (December 1922), pp. 356–357.
↑ 23.0 23.1 23.2 On the relation between the masses and luminosities of the stars, A. S. Eddington, Monthly Notices of the Royal Astronomical Society 84 (March 1924), pp. 308–332.
↑ The search for white dwarfs, W. J. Luyten, Astronomical Journal 55, #1183 (April 1950), pp. 86–89.
↑ 25.0 25.1 25.2 25.3 A Catalog of Spectroscopically Identified White Dwarfs, George P. McCook and Edward M. Sion, The Astrophysical Journal Supplement Series 121, #1 (March 1999), pp. 1–130.
↑ 26.0 26.1 A Catalog of Spectroscopically Confirmed White Dwarfs from the Sloan Digital Sky Survey Data Release 4, Daniel J. Eisenstein, James Liebert, Hugh C. Harris, S. J. Kleinman, Atsuko Nitta, Nicole Silvestri, Scott A. Anderson, J. C. Barentine, Howard J. Brewington, J. Brinkmann, Michael Harvanek, Jurek Krzesiński, Eric H. Neilsen, Jr., Dan Long, Donald P. Schneider, and Stephanie A. Snedden, The Astrophysical Journal Supplement Series 167, #1 (November 2006), pp. 40–58.
↑ The Lowest Mass White Dwarf, Mukremin Kulic, Carlos Allende Prieto, Warren R. Brown, and D. Koester, The Astrophysical Journal 660, #2 (May 2007), pp. 1451–1461.
↑ 28.0 28.1 White dwarf mass distribution in the SDSS, S. O. Kepler, S. J. Kleinman, A. Nitta, D. Koester, B. G. Castanheira, O. Giovannini, A. F. M. Costa, and L. Althaus, Monthly Notices of the Royal Astronomical Society 375, #4 (March 2007), pp. 1315–1324.
↑ Masses and radii of white-dwarf stars. III - Results for 110 hydrogen-rich and 28 helium-rich stars, H. L. Shipman, The Astrophysical Journal 228 (February 15, 1979), pp. 240–256.
↑ Exotic Phases of Matter in Compact Stars, Fredrik Sandin, licentiate thesis, Luleå University of Technology, May 8, 2005.
↑ The Age and Progenitor Mass of Sirius B, James Liebert, Patrick A. Young, David Arnett, J. B. Holberg, and Kurtis A. Williams, The Astrophysical Journal 630, #1 (September 2005) pp. L69–L72.
↑ The Densities of Visual Binary Stars, E. Öpik, The Astrophysical Journal 44 (December 1916), pp. 292–302.
↑ The Relativity Displacement of the Spectral Lines in the Companion of Sirius, Walter S. Adams, Proceedings of the National Academy of Sciences of the United States of America 11, #7 (July 1925), pp. 382–387.
↑ 36.0 36.1 36.2 On Dense Matter, R. H. Fowler, Monthly Notices of the Royal Astronomical Society 87 (1926), pp. 114–122.
↑ The Development of the Quantum Mechanical Electron Theory of Metals: 1900-28, Lillian H. Hoddeson and G. Baym, Proceedings of the Royal Society of London, Series A, Mathematical and Physical Sciences 371, #1744 (June 10, 1980), pp. 8–23.
↑ 38.0 38.1 38.2 38.3 38.4 Estimating Stellar Parameters from Energy Equipartition, ScienceBits. Accessed on line May 9, 2007.
↑ Lecture 12 - Degeneracy pressure, Rachel Bean, lecture notes, Astronomy 211, Cornell University. Accessed on line September 21, 2007.
↑ Über die Grenzdichte der Materie und der Energie, Wilhelm Anderson, Zeitschrift für Physik 56, #11–12 (November 1929), pp. 851–856.
↑ 41.0 41.1 The Equilibrium of Dense Stars, Edmund C. Stoner, Philosophical Magazine (7th series) 9 (1930), pp. 944–963.
↑ The Maximum Mass of Ideal White Dwarfs, S. Chandrasekhar, The Astrophysical Journal 74, #1 (July 1931), pp. 81–82.
↑ 43.0 43.1 43.2 The Highly Collapsed Configurations of a Stellar Mass (second paper), S. Chandrasekhar, Monthly Notices of the Royal Astronomical Society, 95 (1935), pp. 207–225.
↑ The Nobel Prize in Physics 1983, Nobel Foundation. Accessed on line May 4, 2007.
↑ 45.0 45.1 The Possible White Dwarf-Neutron Star Connection, R. Canal and J. Gutierrez, arXiv:astro-ph/9701225v1, January 29, 1997.
↑ 46.0 46.1 46.2 46.3 46.4 46.5 Type IA Supernova Explosion Models, Wolfgang Hillebrandt and Jens C. Niemeyer, Annual Review of Astronomy and Astrophysics 38 (2000), pp. 191–230.
↑ Theory of Low-Mass Stars and Substellar Objects, Gilles Chabrier and Isabelle Baraffe, Annual Review of Astronomy and Astrophysics 38 (2000), pp. 337–377.
↑ The Hertzsprung-Russell (HR) diagram, Jim Kaler, online article. Accessed on line May 5, 2007.
↑ Standards for Astronomical Catalogues, Version 2.0, section 3.2.2. Accessed on line January 12, 2007.
↑ The Structure, Stability, and Dynamics of Self-Gravitating Systems, Joel E. Tohline, online book. Accessed on line May 30, 2007.
↑ Note on equilibrium configurations for rotating white dwarfs, F. Hoyle, Monthly Notices of the Royal Astronomical Society 107 (1947), pp. 231–236.
↑ Rapidly Rotating Stars. II. Massive White Dwarfs, Jeremiah P. Ostriker and Peter Bodenheimer, The Astrophysical Journal 151 (March 1968), pp. 1089–1098.
↑ 53.0 53.1 53.2 A proposed new white dwarf spectral classification system, E. M. Sion, J. L. Greenstein, J. D. Landstreet, J. Liebert, H. L. Shipman, and G. A. Wegner, The Astrophysical Journal 269, #1 (June 1, 1983), pp. 253–257.
↑ 54.0 54.1 WD 0346+246: A Very Low Luminosity, Cool Degenerate in Taurus, N. C. Hambly, S. J. Smartt, and S. Hodgkin, The Astrophysical Journal 489 (November 1997), pp. L157–L160.
↑ 55.0 55.1 55.2 55.3 55.4 55.5 55.6 55.7 White dwarfs, Gilles Fontaine and François Wesemael, in Encyclopedia of Astronomy and Astrophysics, edited by Paul Murdin, Bristol and Philadelphia: Institute of Physics Publishing and London, New York and Tokyo: Nature Publishing Group, 2001. ISBN 0333750888.
↑ X-ray emission from isolated hot white dwarfs, J. Heise, Space Science Reviews 40 (February 1985), pp. 79–90.
↑ On the theory of white dwarf stars. I. The energy sources of white dwarfs, L. Mestel, Monthly Notices of the Royal Astronomical Society 112 (1952), pp. 583–597.
↑ White Dwarf Stars and the Hubble Deep Field, S. D. Kawaler, pp. 252–271 in The Hubble Deep Field: Proceedings of the Space Telescope Science Institute Symposium, held in Baltimore, Maryland, May 6–9, 1997, edited by Mario Livio, S. Michael Fall, and Piero Madau, Space Telescope Science Institute symposium series, 11, New York: Cambridge University Press, 1998, ISBN 0521630975.
↑ The Chemical Evolution of Cool White Dwarfs and the Age of the Local Galactic Disk, P. Bergeron, Maria Teresa Ruiz, and S. K. Leggett, The Astrophysical Journal Supplement Series 108, #1 (January 1997), pp. 339–387.
↑ 60.0 60.1 Testing White Dwarf Crystallization Theory with Asteroseismology of the Massive Pulsating DA Star BPM 37093, T. S. Metcalfe, M. H. Montgomery, and A. Kanaan, The Astrophysical Journal 605, #2 (April 2004), pp. L133–L136.
↑ Crystallization of carbon-oxygen mixtures in white dwarfs, J. L. Barrat, J. P. Hansen, and R. Mochkovitch, Astronomy and Astrophysics 199, #1–2 (June 1988), pp. L15–L18.
↑ The Status of White Dwarf Asteroseismology and a Glimpse of the Road Ahead, D. E. Winget, Baltic Astronomy 4 (1995), pp. 129–136.
↑ Diamond star thrills astronomers, David Whitehouse, BBC News, February 16, 2004. Accessed on line January 6, 2007.
↑ Press release, Harvard-Smithsonian Center for Astrophysics, 2004.
↑ Whole Earth Telescope observations of BPM 37093: a seismological test of crystallization theory in white dwarfs, A. Kanaan, A. Nitta, D. E. Winget, S. O. Kepler, M. H. Montgomery, T. S. Metcalfe, et al., arXiv:astro-ph/0411199v1, November 8, 2004.
↑ Asteroseismology of the Crystallized ZZ Ceti Star BPM 37093: A Different View, P. Brassard and G. Fontaine, The Astrophysical Journal 622, #1 (March 2005), pp. 572–576.
↑ III/235A: A Catalogue of Spectroscopically Identified White Dwarfs, G.P. McCook and E.M. Sion, on line at the Centre de Données astronomiques de Strasbourg. Accessed on line May 9, 2007.
↑ 68.0 68.1 The Cool White Dwarf Luminosity Function and the Age of the Galactic Disk, S. K. Leggett, Maria Teresa Ruiz, and P. Bergeron, The Astrophysical Journal 497 (April 1998), pp. 294–302.
↑ Discovery of New Ultracool White Dwarfs in the Sloan Digital Sky Survey, Evalyn Gates, Geza Gyuk, Hugh C. Harris, Mark Subbarao, Scott Anderson, S. J. Kleinman, James Liebert, Howard Brewington, J. Brinkmann, Michael Harvanek, Jurek Krzesinski, Don Q. Lamb, Dan Long, Eric H. Neilsen, Jr., Peter R. Newman, Atsuko Nitta, and Stephanie A. Snedden, The Astrophysical Journal 612, #2 (September 2004), pp. L129–L132.
↑ The Moment of Creation: Big Bang Physics from Before the First Millisecond to the Present Universe, James S. Trefil, Mineola, New York: Dover Publications, 2004. ISBN 0486438139.
↑ Théorie du débit d'énergie des naines blanches, Evry Schatzman, Annales d'Astrophysique 8 (January 1945), pp. 143–209.
↑ 72.0 72.1 72.2 72.3 72.4 72.5 Physics of white dwarf stars, D. Koester and G. Chanmugam, Reports on Progress in Physics 53 (1990), pp. 837–915.
↑ 73.0 73.1 White Dwarf Stars, Steven D. Kawaler, in Stellar remnants, S. D. Kawaler, I. Novikov, and G. Srinivasan, edited by Georges Meynet and Daniel Schaerer, Berlin: Springer, 1997. Lecture notes for Saas-Fee advanced course number 25. ISBN 3540615202.
↑ List of Known White Dwarfs, Gerard P. Kuiper, Publications of the Astronomical Society of the Pacific 53, #314 (August 1941), pp. 248–252.
↑ The Spectra and Luminosities of White Dwarfs, Willem J. Luyten, Astrophysical Journal 116 (September 1952), pp. 283–290.
↑ Stellar atmospheres, Jesse Leonard Greenstein, in Stars and Stellar Systems, vol. 6, Stellar Atmospheres, edited by J. L. Greenstein, Chicago: University of Chicago Press, 1960.
↑ The magnetic field of massive rotating bodies, P. M. S. Blackett, Nature 159, #4046 (May 17, 1947), pp. 658–666.
↑ Patrick Maynard Stuart Blackett, Baron Blackett, of Chelsea, 18 November 1897-13 July 1974, Bernard Lovell, Biographical Memoirs of Fellows of the Royal Society 21 (November 1975), pp. 1–115.
↑ Coherent Mechanisms of Radio Emission and Magnetic Models of Pulsars, V. L. Ginzburg, V. V. Zheleznyakov, and V. V. Zaitsev, Astrophysics and Space Science 4 (1969), pp. 464–504.
↑ Discovery of Circularly Polarized Light from a White Dwarf, James C. Kemp, John B. Swedlund, J. D. Landstreet, and J. R. P. Angel, The Astrophysical Journal 161 (August 1970), pp. L77–L79.
↑ The fraction of DA white dwarfs with kilo-Gauss magnetic fields, S. Jordan, R. Aznar Cuadrado, R. Napiwotzki, H. M. Schmid, and S. K. Solanki, Astronomy and Astrophysics 462, #3 (February 11, 2007), pp. 1097–1101.
↑ The True Incidence of Magnetism Among Field White Dwarfs, James Liebert, P. Bergeron, and J. B. Holberg, Astronomical Journal 125, #1 (January 2003), pp. 348–353.
↑ 85.0 85.1 85.2 Mapping the Instability Domains of GW Vir Stars in the Effective Temperature-Surface Gravity Diagram, P.-O. Quirion, G. Fontaine, and P. Brassard, The Astrophysical Journal Supplement Series 171, #1 (July 2007), pp. 219–248.
↑ Ultrashort-Period Stellar Oscillations. I. Results from White Dwarfs, Old Novae, Central Stars of Planetary Nebulae, 3C 273, and Scorpius XR-1, George M. Lawrence, Jeremiah P. Ostriker, and James E. Hesser, The Astrophysical Journal 148, #3 (June 1967), pp. L161–L163.
↑ A New Short-Period Blue Variable, Arlo U. Landolt, The Astrophysical Journal 153, #1 (July 1968), pp. 151–164.
↑ Detection of non-radial g-mode pulsations in the newly discovered PG 1159 star HE 1429-1209, T. Nagel and K. Werner, Astronomy and Astrophysics 426 (2004), pp. L45–L48.
↑ The Extent and Cause of the Pre-White Dwarf Instability Strip, M. S. O'Brien, The Astrophysical Journal 532, #2 (April 2000), pp. 1078–1088.
↑ 91.0 91.1 How Massive Single Stars End Their Life, A. Heger, C. L. Fryer, S. E. Woosley, N. Langer, and D. H. Hartmann, The Astrophysical Journal 591, #1 (2003), pp. 288–300.
↑ The End of the Main Sequence, Gregory Laughlin, Peter Bodenheimer, and Fred C. Adams, Astrophysical Journal 482, #1 (June 10, 1997), pp. 420–432.
↑ 93.0 93.1 Stars Beyond Maturity, Simon Jeffery, online article. Accessed on line May 3, 2007.
↑ Helium core white dwarf evolution—including white dwarf companions to neutron stars, M. J. Sarna, E. Ergma, and J. Gerskevits, Astronomische Nachrichten 322, #5/6 (December 2001), pp. 405–410.
↑ The formation of helium white dwarfs in close binary systems - II, O. G. Benvenuto, M. A. De Vito, Monthly Notices of the Royal Astronomical Society 362, #3 (September 2005), pp. 891–905.
↑ Formation of undermassive single white dwarfs and the influence of planets on late stellar evolution, G. Nelemans and T. M. Tauris, Astronomy and Astrophysics 335 (July 1998), pp. L85–L88.
↑ "Planet diet helps white dwarfs stay young and trim", NewScientist.com news service (18 January 2008).
↑ the evolution of low-mass stars, Vik Dhillon, lecture notes, Physics 213, University of Sheffield. Accessed on line May 3, 2007.
↑ the evolution of high-mass stars, Vik Dhillon, lecture notes, Physics 213, University of Sheffield. Accessed on line May 3, 2007.
↑ Strange quark matter in stars: a general overview, Jürgen Schaffner-Bielich, Journal of Physics G: Nuclear and Particle Physics 31, #6 (2005), pp. S651–S657; also arXiv:astro-ph/0412215v1.
↑ Evolution of 8–10 solar mass stars toward electron capture supernovae. I - Formation of electron-degenerate O + Ne + Mg cores, Ken'ichi Nomoto, The Astrophysical Journal 277 (February 15, 1984), pp. 791–805.
↑ The evolution and explosion of massive stars, S. E. Woosley, A. Heger, and T. A. Weaver, Reviews of Modern Physics 74, #4 (October 2002), pp. 1015–1071.
↑ Chandra and FUSE spectroscopy of the hot bare stellar core H 1504+65, K. Werner, T. Rauch, M. A. Barstow, and J. W. Kruk, Astronomy and Astrophysics 421 (2004), pp. 1169–1183.
↑ On the interpretation and implications of nova abundances: an abundance of riches or an overabundance of enrichments, Mario Livio and James W. Truran, The Astrophysical Journal 425, #2 (April 1994), pp. 797–801.
↑ 105.0 105.1 105.2 A dying universe: the long-term fate and evolution of astrophysical objects, Fred C. Adams and Gregory Laughlin, Reviews of Modern Physics 69, #2 (April 1997), pp. 337–372.
↑ Comet clash kicks up dusty haze, BBC News, February 13, 2007. Accessed on line September 20, 2007.
↑ A Debris Disk around the Central Star of the Helix Nebula?, K. Y. L. Su, Y.-H. Chu, G. H. Rieke, P. J. Huggins, R. Gruendl, R. Napiwotzki, T. Rauch, W. B. Latter, and K. Volk, The Astrophysical Journal 657, #1 (March 2007), pp. L41–L45.
↑ The Dust Cloud around the White Dwarf G29-38, William T. Reach, Marc J. Kuchner, Ted von Hippel, Adam Burrows, Fergal Mullally, Mukremin Kilic, and D. E. Winget, The Astrophysical Journal 635, #2 (December 2005), pp. L161–L164.
↑ Presupernova Evolution of Accreting White Dwarfs with Rotation, S.-C. Yoon and N. Langer, Astronomy and Astrophysics 419, #2 (May 2004), pp. 623–644. Accessed on line May 30, 2007.
↑ Theoretical light curves for deflagration models of type Ia supernova, S. I. Blinnikov, F. K. Röpke, E. I. Sorokina, M. Gieseler, M. Reinecke, C. Travaglio, W. Hillebrandt, and M. Stritzinger, Astronomy and Astrophysics 453, #1 (July 2006), pp.229–240.
↑ Imagine the Universe! Cataclysmic Variables, fact sheet at NASA Goddard. Accessed on line May 4, 2007.
↑ 112.0 112.1 Introduction to Cataclysmic Variables (CVs), fact sheet at NASA Goddard. Accessed on line May 4, 2007.
White Dwarf Stars, Steven D. Kawaler, in Stellar remnants, S. D. Kawaler, I. Novikov, and G. Srinivasan, edited by Georges Meynet and Daniel Schaerer, Berlin: Springer, 1997. Lecture notes for Saas-Fee advanced course number 25. ISBN 3540615202.
Black holes, white dwarfs, and neutron stars: the physics of compact objects, Stuart L. Shapiro and Saul A. Teukolsky, New York: Wiley, 1983. ISBN 0471873179.
Asteroseismology of white dwarf stars, D. E. Winget, Journal of Physics: Condensed Matter 10, #49 (December 14, 1998), pp. 11247–11261, doi:10.1088/0953-8984/10/49/014.
White Dwarfs and Dark Matter, B. K. Gibson and C. Flynn, Science 292, #5525 (June 22, 2001), p. 2211, doi:10.1126/science.292.5525.2211a, PMID 11423620.
White dwarf stars with carbon atmospheres, P. Dufour, James Liebert, G. Fontaine, and N. Behara, Nature 450 (November 22, 2007), pp. 522–524, doi:10.1038/nature06318, arΧiv:0711.3227.

References: §1
 §2
 V. 
 V. 
 V. 
 V.