Gravitational Luminosity Research Articles

On the role of magnetars-like magnetic fields into the dynamics and gravitational wave emission of binary neutron stars

Modelling as a dipole the magnetic interaction of a binary system of neutron stars, we are able to include the magnetic effects in the Newtonian and in the inspiral dynamics of the system using an equivalent one-body description. Furthermore, in the inspiral stage we determine the role of the magnetic interaction in the waveforms generated by the system and obtain explicit formulas for the decrease in the separation of the stars, the time to reach a minimal radius, the gravitational luminosity and the change of gravitational wave frequency, all this within the quadrupole approximation. For the magnitude of the magnetic field that is consider to exist in these binaries $\sim 10^{16} {\rm G}$ we are able to show that its effect on the observable quantities is of the order of the 2PN correction, already close to the detection range of the gravitational waves observatories. %} We also discuss cases in which the magnetic field could have a more significant influence.

Does gravitational radiation impact the stellar habitable zone?

Substellar objects of ultrashort periods (less than 50 min) orbiting central stars and many ultracompact star binary systems of even smaller periods (less than 10 min) have been optically detected in the last few years. Their gravitational luminosities can be of the same order or even much greater than their electromagnetic counterparts thereby also comprising a special class of targets for the Large Interferometer Space Antenna (LISA). In this paper, it is argued that the “gravitational illumination” of such systems may alter significantly the standard electromagnetic stellar habitable zone as long as a fraction of its gravitational energy is converted into heat. An analytical formula for the habitable zone is derived by assuming that the planet is simultaneously irradiated by electromagnetic and gravitational luminosities. The effect is quantified and some examples are discussed based on the available observations.

Gravitational waves from fast-spinning white dwarfs

ABSTRACT Two mechanisms of gravitational waves (GWs) emission in fast-spinning white dwarfs (WDs) are investigated: accretion of matter and magnetic deformation. In both cases, the GW emission is generated by an asymmetry around the rotation axis of the star. However, in the first case, the asymmetry is due to the amount of accreted matter on the magnetic poles, while in the second case it is due to the intense magnetic field. We have estimated the GW amplitude and luminosity for three binary systems that have a fast-spinning magnetized WD, namely, AE Aquarii, AR Scorpii, and RX J0648.0−4418. We find that, for the first mechanism, the systems AE Aquarii and RX J0648.0−4418 can be observed by the space detectors BBO and DECIGO if they have an amount of accreted mass of δm ≥ 10−5 M⊙. For the second mechanism, the three systems studied require that the WD have a magnetic field above ∼109 G to emit GWs that can be detected by BBO. We also verified that, in both mechanisms, the gravitational luminosity has an irrelevant contribution to the spin-down luminosity of these three systems. Therefore, other mechanisms of energy emission are needed to explain the spin-down of these objects.

Gravitational waves from ultra-short period exoplanets

ABSTRACT In the last two decades, thousands of extrasolar planets were discovered based on different observational techniques, and their number must increase substantially in virtue of the ongoing and near-future approved missions and facilities. It is shown that interesting signatures of binary systems from nearby exoplanets and their parent stars can also be obtained measuring the pattern of gravitational waves (GWs) that will be made available by the new generation of detectors including the space-based LISA (Laser Interferometer Space Antenna) observatory. As an example, a subset of exoplanets with extremely short periods (less than 80 min) is discussed. All of them have gravitational luminosity, LGW ∼ 1030 erg s−1, strain h ∼ 10−22, frequencies fGW > 10−4 Hz, and, as such, are within the standard sensitivity curve of LISA. Our analysis suggests that the emitted GW pattern may also provide an efficient tool to discover ultra-short period exoplanets.

N-body simulations of gravitational redshifts and other relativistic distortions of galaxy clustering

Large redshift surveys of galaxies and clusters are providing the first opportunities to search for distortions in the observed pattern of large-scale structure due to such effects as gravitational redshift. We focus on non-linear scales and apply a quasi-Newtonian approach using N-body simulations to predict the small asymmetries in the cross-correlation function of two galaxy different populations. Following recent work by Bonvin et al., Zhao and Peacock and Kaiser on galaxy clusters, we include effects which enter at the same order as gravitational redshift: the transverse Doppler effect, light-cone effects, relativistic beaming, luminosity distance perturbation and wide-angle effects. We find that all these effects cause asymmetries in the cross-correlation functions. Quantifying these asymmetries, we find that the total effect is dominated by the gravitational redshift and luminosity distance perturbation at small and large scales, respectively. By adding additional subresolution modelling of galaxy structure to the large-scale structure information, we find that the signal is significantly increased, indicating that structure on the smallest scales is important and should be included. We report on comparison of our simulation results with measurements from the SDSS/BOSS galaxy redshift survey in a companion paper.

Gravitational luminosity of a hot plasma in $$R^{2}$$ R 2 gravity

The R^{2}-gravity contribution to energy loss of a hot plasma due to the gravitational bremsstrahlung is calculated in the linearized theory on the basis of classical Coulomb scattering of plasma constituents in small-angle scattering approximation. The explicit dependence of the gravitational luminosity on the plasma temperature is derived and its relevance to the Einstein gravity is demonstrated. The result when applied to the Sun as a hot plasma, shows very good agreement with available data.

Gravitational effects from earthquakes

Two types of propagating gravitational effects, from the mass redistribution within the Earth due to a large earthquake, are investigated: (i) the velocity of the change of the Newtonian potential field; and (ii) the gravitational luminosity of the seismic source. The mass redistribution caused by an earthquake and the resulting change in the gravitational potential field is computed through application of geophysical dislocation theory. The global mass redistribution is postulated to be progressive, starting at the instant (and location) of the nucleation of the earthquake fault rupture, and then spreading globally at the velocities of various seismic waves. Information about the changes of the gravitational potential is postulated to travel at the velocity of light. Superconducting gravimeters (SG) can resolve changes of the order of 10 nGal, i.e., (10–9 cm/s2) (1 Gal = 0.001 0197g), sufficient to detect the changes in the potential field. The time difference between observation of the change of the potential field and the arrival of the primary seismic wave from the earthquake would allow a crude estimation of the velocity of the gravitational effect. A preliminary search for the preseismic gravitational signal using an SG has given inconclusive results, primarily due to the limitations of the spline curve fitting methods. Despite this, we suggest that the observation of preseismic gravitational potential changes should be feasible, with the existing array of SGs in the Global Geodynamics Project (GGP) network, and by detectors designed to observe gravitational radiation (e.g., the Laser Interferometer Gravitational-wave Observatory (LIGO)). We have used published values of the changes in the Earth's inertia tensor due to the Alaska earthquake of 1964 to estimate the magnitude of the metric perturbation of the gravitational wave produced by such an earthquake. The gravitational luminosity is estimated at 1.90 × 10–10erg/s (1 erg/s = 10–7 W = 1 J/s). PACS Nos.: 95.55.Ym, 04.80.Nn, 91.30.Px

Gravitational radiation from dual neutron star elliptical binaries

General expressions are derived for the gravitational radiation incident on earth due to elliptical binary systems in the Galaxy. These results are applied to dual neutron star elliptical binaries. Calculations show that eccentric dual neutron star binaries lead to a moderate increase in gravitational flux density compared with circular systems for frequencies above approximately 0.0001 Hz. Tables of various quantities such as average gravitational luminosity, number of sources per unit bandwidth, energy spectral flux density, and gravitational wave strain density are given.

Relaxation of Mass-Gaining Stars

The study of relaxing low-mass stars, after gaining mass, to their corresponding main-sequence counterparts is presented. An initial mass of the star was 0.56 M⊙ which was gaining mass at a rate increasing gradually from about 10−10 to about 10−8 M⊙y−1 . The initial chemical composition used for computation was: 75% H, 22.3% He, and 2.7% heavy elements. The mass-gaining stellar model is assumed to be spherically symmetric and in hydrostatic and thermal equilibrium; also it is assumed that mass is absorbed through the stellar envelope from a uniformly distributed outer shell. A sequence of static models was calculated with time steps between the models chosen in such a way as to maintain the changes in physical variables with certain limits from one model to the next. This series of mass-gaining calculations was carried out to the model of 0.835 M⊙. Another series of calculations was carried out in order to investigate the effects of stopping the mass transfer and allowing the star to relax. Each of the twelve selected mass-gaining models was used as the starting point for one of these relaxation sequences; and for each of these twelve masses, a zero-age main sequence model was calculated. The relaxation models were calculated from the same evolutionary technique except that the mass-transfer rate was set to zero. The criterion for stopping these relaxation runs was that the gravitational luminosity term in the envelope should have returned to the main sequence value. An interesting result of these calculations is the finding that in this region of the main sequence where stars have radiative cores, mass-gaining stars develop convective cores. In this particular model sequence, the convective instability first became evident in the model of 0.7125 M⊙ with the logorithm of the central temperature of 7.047. The result of the relaxation calculations shows that, in each case, the star did relax to its corresponding main sequence position. In general, the relaxation process compares favorably with the thermal time scale for these stars. For the model of 0.745 M⊙ at the time when the luminosity increases, indicating that the effective source is reaching the surface, the convective core begins to disappear. The star then decreases its surface temperature, moving to the right in the H-R diagram, while the convective core disappears completely. The H-R diagram track then turns upward toward its proper main sequence location while the contral density and temperature and the luminosity due to nuclear energy generation decrease to their normal values. During this time, the radius and the total luminosity increase to their normal main sequence values.

Gravitational lensing in observational cosmology

This paper reviews some previous theoretical and observational results concerning the various effects of gravitational lensing, and also presents still unpublished results in this field. The theoretical section deals with the Optical Scalar Equation (OSE) approach. We recall the form of these equations, which relate the deformations of the cross sectional area of a light beam to the material and energetic distribution it encounters, via the two basic contributions to lensing, the matter or Ricci term and the shear term. The introduction of a new distance, the optical distance, allows to write the OSE in a simplified way from which new solutions are easily derived. We demonstrate here that a general form may be obtained for the amplification formula in the exact relativistic treatment, provided the Universe is assumed to be Friedmannian in the mean. New results are also presented concerning the probability distribution of amplifications, the relation from matter term to shear terms (the first ones give the mean of the second ones) and the problem of energy conservation. We recall how our method let to an analytical formula yielding the amplification by any number of lenses placed anywhere along the line of sight and present new general solutions for lensing by large scale density inhomogeneities. The gravitational redshift effects are also considered, either due to the crossing by photons of inhomogeneities, or intrinsic to them ; generalized solutions to the last problem are given. Some observational evidence concerning various lensing effects, either statistical or applying to individual sources, are considered. We first recall how the dependence of the amplification formula on the various physical parameters points towards the optimisation of lensing by very rich clusters of galaxies lying at redshifts around 0.7, which may give rise to very large amplifications for reasonable values of the density parameter. Recent results concerning a statistical effect of amplification of Brightest Cluster Galaxies by foreground clusters are analysed, including the discussion of a selection effect precisely due to gravitational luminosity amplification. It results in an artificial increase of the deceleration parameter of the Universe measured from the Hubble diagram of these objects. We recall our proposal that the sample of distant 3C radiogalaxies of redshift > 1 is strongly perturbed by lensing effects, mostly by foreground clusters of galaxies (i.e. only the luminosity is changed without image multiplication), but also for some objects by galaxies, producing gravitational mirages. The case of 3C324, for which definite evidence for multiple imaging has been recently obtained, is described, including detailed modelling of the lensing configuration. We present a highly significant statistical effect of lensing on absorption line QSOs due to matter lying at the absorption redshifts. Microlensing is also considered, and we recall our recent proposal that the variability of some among the OVV QSOs turning to BL Lac at maximum brightness, like the eruptive object 0846 +51W1, is a consequence of microlensing by stars or compact objects constituting foreground galaxy halos. Finally, discrepant redshift associations are considered. We recall how the case of anomalous quintets of galaxies have been explained by the gravitational lensing effects of quartets halos on background galaxies. Then we present evidence that the Arp QSO-galaxy associations may be the result of the combined lensing effects of several superposed galaxies, groups and clusters.

X-Ray Emission from Cataclysmic Variables with Accretion Disks - Part Two - Extreme Ultraviolet Soft X-Ray Radiation

view Abstract Citations (162) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS X-ray emission from cataclysmic variables with accretion disks. II. EUV/soft X-ray radiation. Patterson, J. ; Raymond, J. C. Abstract About half of the gravitational luminosity released by gas accreting onto a white dwarf through a disk should emerge from the star/disk boundary layer. For the accretion rates present in many cataclysmic variables, theory predicts that this luminosity should be in the form of an optically thick EUV/soft X-ray component, with Te ≍ (1-3) x 105 K. We compare the theoretical predictions with presently available soft X-ray observations and find satisfactory agreement. Previous doubts on this point were based on inappropriate choices for several critical parameters: white dwarf mass, interstellar column density, and the space density of classical novae. We also attempt to constrain the boundary layer radiation by comparing observed and predicted strengths of the He II λ 1640 and λ 4686 emission lines, assuming that these are produced by photoionization in the upper layers of the disk. The results support the simple optically thick model for high-A systems, but may require complicated X-ray spectra in low-M systems. Publication: The Astrophysical Journal Pub Date: May 1985 DOI: 10.1086/163188 Bibcode: 1985ApJ...292..550P full text sources ADS | data products SIMBAD (14) Related Materials (1) Part 1: 1985ApJ...292..535P

Gravitational radiation of rapidly rotating drop of homogeneous magnetized gravitating liquid near bifurcation point

The total intensity of gravitational radiation of a rapidly rotating magnetized neutron star near the bifurcation point of its shape is calculated. Estimates of gravitational luminosities for recently discovered pulsars with millisecond periods are made.

Gravitational radiation of an isotropic elastic sphere

Within the framework of linearised elastodynamics and gravidynamics the gravitational radiation of an isotropic elastic sphere without internal damping is calculated. After thermal occupation of the energy eigenstates the authors find gravitational luminosities proportional to T2 and T for T<TD and T>>TD, respectively (TD is the Debye temperature). In both cases the luminosity is proportional to the surface of the sphere, although the material is transparent for gravitational radiation.

Thermal gravitational radiation of Fermi gases and Fermi liquids

In view of neutron stars the gravitational radiation power of the thermal ''zero-sound'' phonons of a Fermi liquid and the gravitational bremsstrahlung of a degenerate Fermi gas is calculated on the basis of a hard-sphere Fermi particle model. We find for the gravitational radiation power per unit volume P/sub( s/)approx. =((9..pi..)/sup 1/3//5) x GQ n/sup 5/3/(kT)/sup 4/ h/sup 2/c/sup 5/ and P/sub( g/)approx. =(4/sup 5//5/sup 3/)(3/..pi..)/sup 2/3/ G a/sup 2/n/sup 5/3/(kT)/sup 4//h/sup 2/c/sup 5/ for the cases of ''zero sound'' and bremsstrahlung, respectively. Here Q = 4..pi..a/sup 2/ is the total cross section of the hard-sphere fermions, where a represents the radius of their hard-core potential. The application to very young neutron stars results in a total gravitational luminosity of about 10/sup 31/ erg/sec.