White dwarf cooling and large extra dimensions (original) (raw)
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White Dwarfs as a Source of Constraints on Exotic Physics
Acta Physica Polonica Series B
In this paper we briefly review main ideas underlying the constraints on exotic physics coming from Astrophysics already used by the others. Next we present a new bound coming from the White Dwarf cooling. Such stringent bound is possible due to accurate measurements offered by astroseismology. Specifically we consider the G117-B15A pulsating white dwarf (ZZ Ceti star) for which the speed of the period increase has been accurately measured for its fundamental oscillation mode. It has been claimed that this mode detected in G117-B15A is perhaps the most stable oscillation ever recorded in the optical band. Then we review our result concerning the bounds on compactification scale in the theory with large extra dimensions according to Arkani-Hamed, Dimopoulos and Dvali. Because an additional channel of energy loss (Kaluza--Klein gravitons) would speed up the cooling rate, one is able to use the aforementioned stability to derive a bound on compactification scale. We find the lower boun...
White Dwarf Constraints On Exotic Physics
Astrophysics and Space Science, 2003
Nonstandard theories of fundamental interactions typically predict the existence of new kinds of weakly interacting particles. These can escape freely from stellar interiors and act as additional source of cooling. Considerable agreement of a variety of astrophysical observations with standard physics can serve as a source of constraints on non-standard ideas. In this paper we consider G117-B15A pulsating white dwarf for which the secular rate, at which the period of its fundamental mode increases, has been accurately measured. This star has been claimed the most stable oscillator ever recorded in the optical band. Because an additional channel of energy loss would speedup the cooling rate, one is able to use this stability to derive a bound on axion mass and on theories with large extra dimensions. We also point to the possibility of using similar arguments to constrain supersymmetric paticles.
Stellar evolution and large extra dimensions
Physics Letters B, 2000
We discuss in detail the information on large extra dimensions which can be derived in the framework of stellar evolution theory and observation. The main effect of large extra dimensions arises from the production of the Kaluza-Klein (KK) excitations of the graviton. The KK-graviton and matter interactions are of gravitational strength, so the KK states never become thermalized and always freely escape. In this paper we first pay attention to the sun. Production of KK gravitons is incompatible with helioseismic constraints unless the 4+n dimensional Planck mass M s exceeds 300 Gev/c 2 . Next we show that stellar structures in their advanced phase of H burning evolution put much more severe constraints, M s > 3 − 4 TeV/c 2 , improving on current laboratory lower limits.
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.
An upper limit to the secular variation of the gravitational constant from white dwarf stars
Journal of Cosmology and Astroparticle Physics, 2011
A variation of the gravitational constant over cosmological ages modifies the main sequence lifetimes and white dwarf cooling ages. Using an state-of-the-art stellar evolutionary code we compute the effects of a secularly varying G on the main sequence ages and, employing white dwarf cooling ages computed taking into account the effects of a running G, we place constraints on the rate of variation of Newton's constant. This is done using the white dwarf luminosity function and the distance of the well studied open Galactic cluster NGC 6791. We derive an upper boundĠ/G ∼ −1.8 × 10 −12 yr −1 . This upper limit for the secular variation of the gravitational constant compares favorably with those obtained using other stellar evolutionary properties, and can be easily improved if deep images of the cluster allow to obtain an improved white dwarf luminosity function.
Vibrational Instabilities and Pulsational Properties of Cool White Dwarfs
International Astronomical Union Colloquium
Attention is focused on those aspects of the theory that may be relevant in understanding the nature of ZZ Ceti-type variable white dwarfs. Recent calculations show that the opacity mechanism can drive a large variety of oscillation modes, including the ones that fit observed periods. An estimate of nonlinear effects shows that resonant mode coupling plays a dominant role in determining the finite amplitude behaviour of oscillations and is also probably responsible for rapid amplitude changes observed in these variables.
In-Stabilities of massive white dwarfs in modified gravity
arXiv (Cornell University), 2023
Super-Chandrasekhar white dwarfs are a timely topic in the last years in the scientific community due to its connection to supernovae type Ia (SN Ia). Some early studies tackled the possibility of white dwarfs surpassing the Chandrasekhar limit by means of a magnetic field. More recently modified gravity has been highlighted as the reason for these stars to surpass the Chandrasekhar limit and becoming a supernova progenitor. However, in general simple assumptions are considered for the stellar structure and equation of state (EoS), which can lead to unreliable conclusions. In this work we want to be rigorous and consider a realistic EoS to describe the white dwarfs in general relativity and modified gravity, taking into account nuclear instabilities that limit the maximum mass.
Observation of a variable, ZZ Ceti white dwarf: GD154
Astrophysics and Space Science, 1993
The ZZ Ceti stars form a class of variable white dwarfs: the hydrogen dominated atmosphere ones, which do pulsate in an instability strip in the effective temperature range 13000K-11500K. We know 22 such ZZ Ceti white dwarfs. Their variations are caused by nonradial g-mode pulsations with periods are in the range 100-1000 seconds. A subsample of the ZZ Ceti stars shows amplitude variations on time scales of the order of one month. These variations could be driven by nonlinear phenomena. One of these potentially non-linear pulsators, GD154, is on the red edge of the ZZ Ceti instability strip. It was first observed on May 1977 (Robinson et al. 1978). They obtained a power spectrum dominated by one mode
The structure and stability of massive hot white dwarfs
2021
We investigate the structure and stability against radial oscillations, pycnonuclear reactions, and inverse β-decay of hot white dwarfs. We regard that the fluid matter is made up for nucleons and electrons confined in a Wigner-Seitz cell surrounded by free photons. It is considered that the temperature depends on the mass density considering the presence of an isothermal core. We find that the temperature produces remarkable effects on the equilibrium and radial stability of white dwarfs. The stable equilibrium configuration results are compared with white dwarfs estimated from the Extreme Ultraviolet Explorer Survey and Sloan Digital Sky Survey. We derive masses, radii, and central temperatures for the most massive white dwarfs according to surface gravity and effective temperature reported by the survey. We note that these massive stars are in the mass region where the general relativity effects are important. These stars are near the threshold of instabilities due to radial osci...
Symposium - International Astronomical Union
The rate of change of period with time for the g-mode pulsations in ZZ Ceti stars depends directly on the cooling timescale for a DA white dwarf, and therefore a measurement of its value can yield an evolutionary timescale for the white dwarf. We have obtained an upper limit for the rate of change of the period of the dominant pulsation in the light curve of the ZZ Ceti star G117-B15A of |dP/dt| ≤ 9.9 × 10−15 s/s at the 68% confidence level, equivalent to a timescale for period change of