The rate of change of the gravitational constant and the cooling of white dwarfs

Astronomy and Astrophysics – Astronomy

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Gravitation, Stars: Evolution, White Dwarfs

Scientific paper

In this paper we examine the effects introduced in the luminosity function of white dwarf stars by a change of the gravitational constant during the life of the Universe. A decrease of G induces the expansion of the star and accelerates the cooling process. This effect has noticeable effects on the luminosity function and can be used to set upper bounds on the rate of change of G. The values of the derived upper limit depend on the adopted age of the galactic disc, the position of the cut-off of the white dwarf luminosity function, and the physics of cooling - such as the degree of previous stratification of the chemical constituents of white dwarfs and the phase diagram of the carbon/oxygen (C/O) mixture. For reasonable ages of the solar neighbourhood this method provides G_solar/G<=-(1+/-1)x10^-11 yr^-1 if previously stratified models are adopted and G_solar/G<=-(3^+1_-3)x10^-11 yr^-1 if the distribution of carbon and oxygen is assumed to be constant through the white dwarf. These values are comparable with the upper bound obtained from the binary pulsar, which is considered to be the best constraint on the rate of variation of the gravitational constant.

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