An upper limit to the secular variation of the gravitational constant from white dwarf stars (original) (raw)
Related papers
A new white dwarf constraint on the rate of change of the gravitational constant
Monthly Notices of The Royal Astronomical Society, 2004
In this paper we derive a bound on the rate of change of the gravitational constant G coming from the pulsating white dwarf G117-B15A. This star is a ZZ Ceti pulsator extensively studied with astroseismological techniques for last three decades. The most recent determination of {\dot P} = (2.3 \pm 1.4) * 10^{-15} s/s^{-1} for the 215.2s fundamental mode agrees very well with predictions of the best fit theoretical model. The rate of change of the oscillation period can be explained by two effects: the cooling (dominant factor) and change of gravitational binding energy (residual gravitational contraction). Since the white dwarfs are pulsating in g-modes whose frequencies are related to the Brunt-Vaisala frequency (explicitly dependent on G) observational determination of the change of the period (more precisely the difference between observed and calculated \dot P) can be used to set the upper bound on the rate of change of G. In the light of the current data concerning G117-B15A we derive the following bound: |{\frac {\dot G}{G}}| \leq 4.10 \times 10^{-10} yr^{-1}. Our result is model independent in the sense that it does not need to invoke a concrete physical theory (such like Brans-Dicke theory)underlying the temporal variability of G. We also demonstrate that varying gravitational constant G does not modify cooling of white dwarfs in a significant way. This result implies that some earlier claims present in the literature that varying G can be reflected in the WD luminosity function are not correct.
The evolution of white dwarfs with a varying gravitational constant
Astronomy & Astrophysics, 2011
Context. Within the theoretical framework of some modern unification theories the constants of nature are functions of cosmological time. White dwarfs offer the possibility of testing a possible variation of G and, thus, to place constraints to these theories. Aims. We present full white dwarf evolutionary calculations in the case that G decreases with time.
Journal of Cosmology and Astroparticle Physics, 2013
A secular variation of the gravitational constant modifies the structure and evolutionary time scales of white dwarfs. Using an state-of-the-art stellar evolutionary code and an up-to-date pulsational code we compute the effects of a secularly varying G on the pulsational properties of variable white dwarfs. Comparing the the theoretical results obtained taking into account the effects of a running G with the observed periods and measured rates of change of the periods of two well studied pulsating white dwarfs, G117-B15A and R548, we place constraints on the rate of variation of Newton's constant. We derive an upper boundĠ/G ∼ −1.8 × 10 −10 yr −1 using the variable white dwarf G117-B15A, anḋ G/G ∼ −1.3 × 10 −10 yr −1 using R548. Although these upper limits are currently less restrictive than those obtained using other techniques, they can be improved in a future measuring the rate of change of the period of massive white dwarfs.
Variation of fundamental constants and white dwarfs
Proceedings of the International Astronomical Union, 2019
Theories that attempt to unify the four fundamental interactions and alternative theories of gravity predict time and/or spatial variation of the fundamental constants of nature. Different versions of these theories predict different behaviours for these variations. In consequence, experimental and observational bounds are an important tool to check the validity of such proposals. In this paper, we review constraints on the possible variation of the fundamental constants from astronomical observations and geophysical experiments designed to test the constancy of the fundamental constants of nature over different timescales. We also focus on the limits that can be obtained from white dwarfs, which can constrain the variation of the constants with the gravitational potential.
Universe, 2017
Hot white dwarf stars are the ideal probe for a relationship between the fine-structure constant and strong gravitational fields, providing us with an opportunity for a direct observational test. We study a sample of hot white dwarf stars, combining far-UV spectroscopic observations, atomic physics, atmospheric modelling, and fundamental physics in the search for variation in the fine structure constant. This variation manifests as shifts in the observed wavelengths of absorption lines, such as quadruply ionized iron (FeV) and quadruply ionized nickel (NiV), when compared to laboratory wavelengths. Berengut et al. (Phys. Rev. Lett. 2013, 111, 010801) demonstrated the validity of such an analysis using high-resolution Space Telescope Imaging Spectrograph (STIS) spectra of G191-B2B. We have made three important improvements by: (a) using three new independent sets of laboratory wavelengths; (b) analysing a sample of objects; and (c) improving the methodology by incorporating robust techniques from previous studies towards quasars (the Many Multiplet method). A successful detection would be the first direct measurement of a gravitational field effect on a bare constant of nature. Here we describe our approach and present preliminary results from nine objects using both FeV and NiV.
White dwarf cooling sequences and cosmochronology
EPJ Web of Conferences, 2013
The evolution of white dwarfs is a simple gravothermal process. This means that their luminosity function, i.e. the number of white dwarfs per unit bolometric magnitude and unit volume as a function of bolometric magnitude, is a monotonically increasing function that decreases abruptly as a consequence of the finite age of the Galaxy. The precision and the accuracy of the white dwarf luminosity functions obtained with the recent large surveys together with the improved quality of the theoretical models of evolution of white dwarfs allow to feed the hope that in a near future it will be possible to reconstruct the history of the different Galactic populations.
A Gravitational Redshift Determination of the Mean Mass of White Dwarfs. Da Stars
The Astrophysical Journal, 2010
We measure apparent velocities (v app) of the Hα and Hβ Balmer line cores for 449 non-binary thin disk normal DA white dwarfs (WDs) using optical spectra taken for the ESO SN Ia Progenitor surveY (SPY; Napiwotzki et al. 2001). Assuming these WDs are nearby and co-moving, we correct our velocities to the Local Standard of Rest so that the remaining stellar motions are random. By averaging over the sample, we are left with the mean gravitational redshift, v g : we find v g = v app = 32.57 ± 1.17 km s −1. Using the mass-radius relation from evolutionary models, this translates to a mean mass of 0.647 +0.013 −0.014 M ⊙. We interpret this as the mean mass for all DAs. Our results are in agreement with previous gravitational redshift studies but are significantly higher than all previous spectroscopic determinations except the recent findings of Tremblay & Bergeron (2009). Since the gravitational redshift method is independent of surface gravity from atmosphere models, we investigate the mean mass of DAs with spectroscopic T eff both above and below 12000 K; fits to line profiles give a rapid increase in the mean mass with decreasing T eff. Our results are consistent with no significant change in mean mass: M hot = 0.640 ± 0.014 M ⊙ and M cool = 0.686 +0.035 −0.039 M ⊙ .
Evolution of white dwarfs as a probe of theories of gravitation: the case of Brans--Dicke
Monthly Notices of the Royal Astronomical Society, 1999
Theories with varying gravitational constant G have long been studied. Among them, the most promising candidates as alternatives to standard general relativity are known as scalar±tensor theories. They are consistent descriptions of the observed Universe as well as the low-energy limit of several pictures of uni®ed interactions. Thus, increasing interest in the astrophysical, gravitational wave and pulsar evolution consequences of such theories has been sparked over the last few years. In this work we study the evolution of white dwarf stars in the framework of the simplest model of scalar±tensor theory: Brans±Dicke gravity. We assume that the star is able to see the cosmological evolution of G (obtained from relativistic equations) while adopting a Newtonian model for describing its structure. This allows us to determine how the G variation affects the energetics of the stellar interior. The white dwarfs are analysed employing a well-tested computer code, with state-of-the-art data for the equation of state, opacities, neutrinos, etc.; all these characteristics are carefully described in the text. We compute the theoretical white dwarf luminosity function and use previous observational data to compare with and extract conclusions on the feasibility of the gravitational theory analysed. We ®nd several striking results. The cooling of white dwarfs is strongly accelerated, particularly for massive stars and low luminosities, even if the q parameter of Brans±Dicke theory is big enough to accord well with any other test of gravitation. This uncommon cooling process translates into several distinctive features of white dwarf evolution, among which are (a) a new pro®le of luminosity versus fractional mass and age, (b) different central temperature versus surface luminosity, (c) low masses of progenitors, and most importantly (d) an appreciable variation in the luminosity function. We ®nally analyse the possibilities of, when precise data with unique interpretation are available, converting this into a powerful new test of gravitation.
Astrophysics and Space Science, 2008
Motivated by the possibility that the fundamental "constants" of nature could vary with time, this paper considers the long term evolution of white dwarf stars under the combined action of proton decay and variations in the gravitational constant. White dwarfs are thus used as a theoretical laboratory to study the effects of possible time variations, especially their implications for the future history of the universe. More specifically, we consider the gravitational constant G to vary according to the parametric relation G = G 0 (1 + t/t ⋆ ) −p , where the time scale t ⋆ is the same order as the proton lifetime t P . We then study the long term fate and evolution of white dwarf stars. This treatment begins when proton decay dominates the stellar luminosity, and ends when the star becomes optically thin to its internal radiation.
New Cooling Sequences for Old White Dwarfs
The Astrophysical Journal, 2010
We present full evolutionary calculations appropriate for the study of hydrogen-rich DA white dwarfs. This is done by evolving white dwarf progenitors from the zero age main sequence, through the core hydrogen burning phase, the helium burning phase and the thermally pulsing asymptotic giant branch phase to the white dwarf stage. Complete evolutionary sequences are computed for a wide range of stellar masses and for two different metallicities: Z = 0.01, which is representative of the solar neighborhood, and Z = 0.001, which is appropriate for the study of old stellar systems, like globular clusters. During the white dwarf cooling stage we compute self-consistently the phase in which nuclear reactions are still important, the diffusive evolution of the elements in the outer layers and, finally, we also take into account all the relevant energy sources in the deep interior of the white dwarf, like the release of latent heat and the release of gravitational energy due to carbon-oxygen phase separation upon crystallization. We also provide colors and magnitudes for these sequences, based on a new set of improved non-gray white dwarf model atmospheres, which include the most up-to-date physical inputs like the Lyα quasi-molecular opacity. The calculations are extended down to an effective temperature of 2,500 K. Our calculations provide a homogeneous set of evolutionary cooling tracks appropriate for mass and age determinations of old DA white dwarfs and for white dwarf cosmochronology of the different Galactic populations.