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BPM 37093
BPM 37093 (V886 Centauri) is a variable white dwarf star of the DAV, or ZZ Ceti, type, with a hydrogen atmosphere and an unusually high mass of approximately 1.1 times the Sun's. It is about 50 light-years from Earth, in the constellation Centaurus, and vibrates; these pulsations cause its luminosity to vary.〔〔 Like other white dwarfs, BPM 37093 is thought to be composed primarily of carbon and oxygen, which are created by thermonuclear fusion of helium nuclei in the triple-alpha process.〔(Late stages of evolution for low-mass stars ), Michael Richmond, lecture notes, Physics 230, Rochester Institute of Technology, accessed online May 3, 2007.〕
In the 1960s, it was predicted that as a white dwarf cools, its material should crystallize, starting at the center.〔Testing White Dwarf Crystallization Theory with Asteroseismology of the Massive Pulsating DA Star BPM 37093, T. S. Metcalfe, M. H. Montgomery, and A. Kanaan, ''Astrophysical Journal'' 605, #2 (April 2004), pp. L133–L136. 〕 When a star pulsates, observing its pulsations gives information about its structure. BPM 37093 was first observed to be a pulsating variable in 1992,〔The discovery of a new DAV star using IUE temperature determination, A. Kanaan, S. O. Kepler, O. Giovannini, and M. Diaz, ''Astrophysical Journal Letters'' 390, #2 (May 10, 1992), pp. L89–L91. 〕 and in 1995 it was pointed out that this yielded a potential test of the crystallization theory.〔The Status of White Dwarf Asteroseismology and a Glimpse of the Road Ahead, D. E. Winget, ''Baltic Astronomy'' 4 (1995), pp. 129–136. 〕 In 2004, Antonio Kanaan and a team of researchers of the Whole Earth Telescope estimated, on the basis of these asteroseismological observations, that approximately 90% of the mass of BPM 37093 had crystallized.〔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., ''Astronomy and Astrophysics'' 432, #1 (March 2005), pp. 219–224. .〕〔〔(BBC News: Diamond star thrills astronomers )〕〔(Press release ), 2004, Harvard-Smithsonian Center for Astrophysics.〕 Other work gives a crystallized mass fraction of between 32% and 82%.〔P. Brassard, G. Fontaine, Asteroseismology of the Crystallized ZZ Ceti Star BPM 37093: A Different View, ''Astrophysical Journal'' 622, #1, pp. 572–576. 〕 Any of these estimates would result in a total crystalline mass in excess of 5 kilograms.
Crystallization of the material of a white dwarf of this type is thought to result in a body-centered cubic lattice of carbon and/or oxygen nuclei, which are surrounded by a Fermi sea of electrons.〔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. 〕
==Nickname and press coverage==
*Since a diamond also consists of crystallized carbon, the star BPM 37093 has been nicknamed ''Lucy'' after The Beatles' hit ''Lucy in the Sky with Diamonds''.〔
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