White Dwarfs as a Source of Constraints on Exotic Physics (original) (raw)
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White dwarf cooling and large extra dimensions
Physical Review D, 2002
Theories of fundamental interactions with large extra dimensions have recently become very popular. Astrophysical bounds from the Sun, red-giants and SN1987a have already been derived by other authors for the theory proposed by Arkani-Hamed, Dimopoulos and Dvali. In this paper we consider G117-B15A pulsating white dwarf (ZZ Ceti star) for which the secular rate at which the period of its fundamental mode increases has been accurately measured and claimed that this mode of G117-B15A is perhaps the most stable oscillation ever recorded in the optical band. 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 theories with large extra dimensions. Within the framework of the theory with large extra dimensions proposed by Arkani-Hamed, Dimopoulos and Dvali we find the lower bound on string comapctification scale which is more stringent than solar or red-giant bounds.
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.
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 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...
Compact objects for everyone: I. White dwarf stars
European Journal of Physics, 2005
Based upon previous discussions on the structure of compact stars geared towards undergraduate physics students, a real experiment involving two upper-level undergraduate physics students, a beginning physics graduate, and two advanced graduate students was conducted. A recent addition to the physics curriculum at Florida State University, The Physics of Stars, sparked quite a few students' interests in the subject matter involving stellar structure. This, coupled with Stars and Statistical Physics by Balian and Blaizot [1] and Neutron Stars for Undergraduates by Silbar and Reddy [2], is the cornerstone of this small research group who tackled solving the structure equations for compact objects in the Summer of 2004. Through the use of a simple finite-difference algorithm coupled to Microsoft Excel and Maple, solutions to the equations for stellar structure are presented in the Newtonian regime appropriate to the physics of white dwarf stars. PACS numbers: 1 I. OVERVIEW OF THE PROJECT
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.
Astronomische Nachrichten, 2002
We discuss basic ideas which were fundamental for the black hole concept. The major goal of the historical part is an attempt to explain the long way to the birth of the black hole concept, since the black hole solution was already found in 1916 by K. Schwarzschild, but the black hole concept was only introduced in 1967 by J.A. Wheeler. We discuss the basic notations of the black hole theory and observational manifestations of black holes. We analyse the possibility to interpret the very peculiar distortion of the Fe ë-line in such a way.
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.
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.
White Dwarf Constraints on Dark Matter Particles
Acta Physica Polonica Series B
Matter budget in the Universe together with primordial nucleosynthesis bounds on baryonic density suggests that dark matter in galaxies should have non-baryonic nature. On the other hand, considerable agreement of a variety of astrophysical observations with standard physics can serve as a source of constraints on non-standard ideas. In this context we consider G117-B15A pulsating white dwarf for which the rate of period change of its fundamental mode has been accurately measured. This star has been claimed the most stable oscillator ever recorded in the optical band. Here we use this object to derive a bound on theories with large extra dimensions as well as to constrain supersymmetric dark matter.