Presence Of Strong Gravitational Fields Research Articles

Measuring the fine structure constant on a white dwarf surface; a detailed analysis of Fe V absorption in G191-B2B

Abstract The gravitational potential φ = GM/Rc2 at the surface of the white dwarf G191-B2B is 10,000 times stronger than that at the Earth’s surface. Numerous photospheric absorption features are detected, making this a suitable environment to test theories in which the fundamental constants depend on gravity. We have measured the fine structure constant, α, at the white dwarf surface, used a newly calibrated Hubble Space Telescope STIS spectrum of G191-B2B, two new independent sets of laboratory Fe V wavelengths, and new atomic calculations of the sensitivity parameters that quantify Fe V wavelength dependency on α. The two results obtained are: Δα/α0 = (6.36 ± 0.35stat ± 1.84sys) × 10−5 and Δα/α0 = (4.21 ± 0.48stat ± 2.25sys) × 10−5. The measurements hint that the fine structure constant increases slightly in the presence of strong gravitational fields. A comprehensive search for systematic errors is summarised, including possible effects from line misidentifications, line blending, stratification of the white dwarf atmosphere, the quadratic Zeeman effect and electric field effects, photospheric velocity flows, long-range wavelength distortions in the HST spectrum, and variations in the relative Fe isotopic abundances. None fully account for the observed deviation but the systematic uncertainties are heavily dominated by laboratory wavelength measurement precision.

Comment on “Neutrino decoherence in presence of strong gravitational fields”

The present work can be regarded as a corollary to the paper titled “Neutrino decoherence in presence of strong gravitational fields”. Specifically, we investigate the gravitationally-induced decoherence on neutrino oscillation from the point of view of a locally inertial observer at rest with neutrino propagation. In so doing, we observe that in the aforementioned reference frame the effects of gravity can become manifest in a non-trivial manner with respect to an observer placed at infinity.

Spectra of Ni V and Fe V in the Vacuum Ultraviolet.

This work presents 97 remeasured Fe V wavelengths (1200-1600 Å) and 123 remeasured Ni V wavelengths (1200-1400 Å) with uncertainties of approximately 2 mÅ. An additional 67 remeasured Fe V wavelengths and 72 remeasured Ni V wavelengths with uncertainties greater than 2 mÅ are also reported. A systematic calibration error is also identified in the previous Ni V wavelengths and is corrected in this work. Furthermore, a new energy level optimization of Ni V is presented that includes level values as well as Ritz wavelengths. This work improves upon the available data used for observations of quadruply ionized nickel (Ni V) in white dwarf stars. This compilation is specifically targeted toward observations of the G191-B2B white dwarf spectrum that has been used to test for variations in the fine structure constant, , in the presence of strong gravitational fields. The laboratory wavelengths for these ions were thought to be the cause of inconsistent conclusions regarding the variation limit of as observed through the white dwarf spectrum. These inconsistencies can now be addressed with the improved laboratory data presented here.

Constraining the magnetic field on white dwarf surfaces; Zeeman effects and fine structure constant variation

ABSTRACT White dwarf (WD) atmospheres are subjected to gravitational potentials around 105 times larger than occur on Earth. They provide a unique environment in which to search for any possible variation in fundamental physics in the presence of strong gravitational fields. However, a sufficiently strong magnetic field will alter absorption line profiles and introduce additional uncertainties in measurements of the fine structure constant. Estimating the magnetic field strength is thus essential in this context. Here, we model the absorption profiles of a large number of atomic transitions in the WD photosphere, including first-order Zeeman effects in the line profiles, varying the magnetic field as a free parameter. We apply the method to a high signal-to-noise, high-resolution, far-ultraviolet Hubble Space Telescope/Space Telescope Imaging Spectrograph spectrum of the WD G191−B2B. The method yields a sensitive upper limit on its magnetic field of B < 2300 G at the 3σ level. Using this upper limit, we find that the potential impact of quadratic Zeeman shifts on measurements of the fine structure constant in G191−B2B is 4 orders of magnitude below laboratory wavelength uncertainties.

Nonlinear wave breaking in self-gravitating viscoelastic quantum fluid

The stability of a viscoelastic self-gravitating quantum fluid has been studied. Symmetry breaking instability of solitary wave has been observed through ‘viscosity modified Ostrovsky equation’ in weak gravity limit. In presence of strong gravitational field, the solitary wave breaks into shock waves. Response to a Gaussian perturbation, the system produces quasi-periodic short waves, which in terns predicts the existence of gravito-acoustic quasi-periodic short waves in lower solar corona region. Stability analysis of this dynamical system predicts gravity has the most prominent effect on the phase portraits, therefore, on the stability of the system. The non-existence of chaotic solution has also been observed at long wavelength perturbation through index value theorem.

Colloquium: Search for a drifting proton-electron mass ratio fromH2

An overview is presented of the H$_2$ quasar absorption method to search for a possible variation of the proton--electron mass ratio $\mu=m_p/m_e$ on a cosmological time scale. Details of the analysis of astronomical spectra, obtained with large 8--10 m class optical telescopes, equipped with high-resolution echelle grating based spectrographs, are explained. The methods and results of the laboratory molecular spectroscopy of H$_2$, in particular the laser-based metrology studies for the determination of rest wavelengths of the Lyman and Werner band absorption lines, are reviewed. Theoretical physics scenarios delivering a rationale for a varying $\mu$ will be discussed briefly, as well as alternative spectroscopic approaches to probe variation of $\mu$, other than the H$_2$ method. Also a recent approach to detect a dependence of the proton-to-electron mass ratio on environmental conditions, such as the presence of strong gravitational fields, will be highlighted. Currently some 56 H$_2$ absorption systems are known and listed. Their usefulness to detect $\mu$-variation is discussed, in terms of column densities and brightness of background quasar sources, along with future observational strategies. The astronomical observations of ten quasar systems analyzed so far set a constraint on a varying proton-electron mass ratio of $|\Delta\mu/\mu| < 5 \times 10^{-6}$ (3-$\sigma$), which is a null result, holding for redshifts in the range $z=2.0-4.2$. This corresponds to look-back times of 10--12.4 billion years into cosmic history. Attempts to interpret the results from these 10 H$_2$ absorbers in terms of a spatial variation of $\mu$ are currently hampered by the small sample size and their coincidental distribution in a relatively narrow band across the sky.

Black holes as QCD laboratories

A precise description of black hole evaporation requires a quantitative understanding of chiral symmetry breaking and confinement in the presence of strong gravitational fields. In this paper, we present a brief review of our recent work on the subject and explain our results in terms of the recently discussed chiral gap effect.

Modified gravity black holes and their observable shadows

The shadows cast by non-rotating and rotating modified gravity black holes are determined by the two parameters mass $$M$$ and angular momentum $$J=Ma$$ . The sizes of the shadows cast by the spherically symmetric static modified gravity–Schwarzschild and modified gravity–Kerr rotating black holes increase significantly as the free parameter $$\alpha $$ is increased from zero. The Event Horizon Telescope shadow image measurements can determine whether Einstein’s general relativity is correct or whether it should be modified in the presence of strong gravitational fields.

Line-driven winds in the presence of strong gravitational fields

We propose a general physical mechanism which could contribute to the formation of fast line-driven outflows at the vicinity of strong gravitational field sources. We argue that the gradient of the gravitational potential plays the same role as the velocity gradient plays in the Sobolev approximation. Both the Doppler effect and gravitational redshifting are taken into account in the Sobolev approximation. The radiation force becomes a function of the local velocity gradient and the gradient of the gravitational potential. The derived equation of motion has a critical point that is different from that of Castor, Abbott and Klein (CAK). A solution, which is continuous through the singular point, is obtained numerically. A comparison with CAK theory is presented. It is shown that the developed theory predicts terminal velocities which are greater than those obtained from the CAK theory.

Matter effects on neutrino oscillations in gravitational and magnetic fields

When neutrinos propagate in a background, their gravitational couplings are modified by their weak interactions with the particles in the background. In a medium that contains electrons but no muons or taons, the matter-induced gravitational couplings of neutrinos are different for the various neutrino flavors, and they must be taken into account in describing the phenomena associated with the neutrino oscillations in the presence of strong gravitational fields. Here we incorporate those couplings in that description, including also the effects of a magnetic field, and consider the implications that they have for the emission of high energy neutrinos in the vicinity of Active Galactic Nuclei.

Neutrino oscillations in strong gravitational fields.

Neutrino oscillations in the presence of strong gravitational fields are studied. We look at very high energy neutrinos ($\sim $1 TeV) emanating from Active Galactic Nuclei (AGN). It is observed that spin flavor resonant transitions of such neutrinos may occur in the vicinity of AGN due to {\it gravitational} effects and due to the presence of a large magnetic field ($\sim $1 Tesla). A point to note is that matter effects (normal MSW transitions) become negligible in comparison o gravitational effects in our scenario.

Transient relativistic thermodynamics and kinetic theory

The paper develops, from both the phenomenological and kinetic points of view, a generalized formulation of irreversible thermodynamics applicable to the description of thermal phenomena in the presence of strong gravitational fields, fast rotation and rapid fluctuations. The coefficients in the generalized transport equations are evaluated explicitly for a relativistic quantum gas.