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At least 397 records · Page 22Linked to original sources
arXiv2007

Can the flyby anomalies be explained by a modification of inertia?

The flyby anomalies are unexplained velocity increases of 3.9, 13.5, 0.1 and 1.8 mm/s observed near closest approach during the Earth flybys of the Galileo, NEAR, Cassini and Rosetta spacecraft. Here, these flybys are modelled using a theory that assumes that inertia is caused by a form of Unruh radiation, modified by a Hubble-scale Casimir effect. This theory predicts that when the craft's accelerations relative to the galactic centre approached zero near closest approach, their inertial masses reduced for about 10^-7 s causing Earthward jumps of 2.6, 1.2, 1.4 and 1.9 mm/s respectively, and, to conserve angular momentum, increases in orbital velocity of a few mm/s that, except NEAR's, were quite close to those observed. However, these results were extremely sensitive to the Hubble constant used. As an experimental test of these ideas, it is proposed that metamaterials could be used to bend Unruh radiation around objects, possibly reducing their inertial mass.

astro-ph↗
arXiv2007

Heavy Cosmic Ray Nuclei from Extragalactic Sources above 'The Ankle'

A very recent observation by the Auger Observatory group claims strong evidence for cosmic rays above 56 EeV being protons from Active Galactic Nuclei. If, as would be expected, the particles above the ankle at about 2 EeV are almost all of extragalactic origin then it follows that the characteristics of the nuclear interactions of such particles would need to be very different from conventional expectation -- a result that follows from the measured positions of 'shower maximum' in the Auger' work. Our own analysis gives a different result, viz that the detected particles are still 'massive' specifically with a mean value of = 2.2 +- 0.8. The need for a dramatic change in the nuclear physics disappears.

astro-ph↗
arXiv2007

Segregation of isotopes of heavy metals due to light-induced drift: results and problems

Atutov and Shalagin (1988) proposed light-induced drift (LID) as a physically well understandable mechanism to explain the formation of isotopic anomalies observed in CP stars. We generalized the theory of LID and applied it to diffusion of heavy elements and their isotopes in quiescent atmospheres of CP stars. Diffusional segregation of isotopes of chemical elements is described by the equations of continuity and diffusion velocity. Computations of the evolutionary sequences for abundances of mercury isotopes in several model atmospheres have been made using the Fortran 90 program SMART, composed by the authors. Results confirm predominant role of LID in separation of isotopes.

astro-ph↗
arXiv2008

The Thickness of High-Redshift Quasar Ionization Fronts as a Constraint on the Ionizing Spectral Energy Distribution

High-redshift quasars (z >~ 6) drive ionization fronts into the intergalactic medium (IGM). If the thickness of the front can be measured, it can provide a novel constraint on the ionizing spectral energy distribution (SED). Here we follow the propagation of an I-front into a uniform IGM, and compute its thickness for a range of possible quasar spectra and ages. We also explore the effects of uniform and non-uniform ionizing backgrounds. We find that even for hard spectra, the fronts are initially thin, with a thickness much smaller than the mean free path of ionizing photons, but the thickness increases as the front approaches equilibrium in 10^8 - 10^9 years, and can eventually significantly exceed simple estimates based on the mean free path. With a high intrinsic hydrogen column density obscuring the source (log(N_H/cm^-2) >~ 19.2) or a hard power-law spectrum combined with some obscuration (e.g. dlog(F_ν)/dlog(ν) >~ -1.2 at log(N_H/cm^-2) >~ 18.0), the thickness of the front exceeds ~1 physical Mpc and may be measurable from the morphology of its redshifted 21cm signal. We find that the highly ionized inner part of the front, which may be probed by Lyman line absorption spectra, remains sharp for bright quasars unless a large obscuring column (log(N_H/cm^-2) >~ 19.2) removes most of their ionizing photons up to ~40 eV. For obscured sources with log(N_H/cm^-2) >~ 19.8, embedded in a significantly neutral IGM, the black Lyman-alpha trough (where the neutral fraction is ~10^-3) underestimates the size of the HII region by a factor of >~4.

astro-ph↗
arXiv2008

The Sunyaev-Zel'dovich Effect On Elliptical Galaxies

The history of discovering of hot gas in galaxies is traced briefly, its main properties are described and the desirability to make them more precise, in particular to obtain additional data on the mass of such gas is pointed out. For this purpose observations of the Sunyaev-Zel'dovich effect on hot gas of coronas of elliptic galaxies are proposed. The absolute and relative disturbances of the cosmic microwave radiation spectrum due to scattering of relic photons by Maxwellian electrons are calculated according the formula of the article. With the example of three elliptic galaxies it is shown that observation of the SZ effect on such galaxies is quite possible. Kinematic SZ effect arising due to peculiar movement and rotation of galaxies is available for observation as well. Such observations combined with X-ray data would make it possible to get more about properties of galactic gas, to obtain additional information on rotation of galaxies, on possible accreting gas flows and on hot galactic wind.

astro-ph↗
arXiv2007

Black hole entropy and the holographic principle

Black holes monopolize nowadays the center stage of fundamental physics. Yet, they are poorly understood objects. Notwithstanding, from their generic properties, one can infer important clues to what a fundamental theory, a theory that includes gravitation and quantum mechanics, should give. Here we review the classical properties of black holes and their associated event horizons, as well as the quantum and thermodynamic properties, such as the temperature, derived from the Hawking radiation, and the entropy. Then, using the black hole properties we discuss a universal bound on the entropy for any object, or for any given region of spacetime, and finally we present the arguments, first given by 't Hooft, that, associating entropy with the number of quantum degrees of freedom, i.e., the logarithm of quantum states, via statistical physics, leads to the conclusion that the degrees of freedom of a given region are in the area A of the region, rather than in its volume V as naively could be thought. Surely, a fundamental theory has to take this in consideration.

gr-qc↗
arXiv2007

A Survey of Compact Star Clusters in the S-W Field of the M31 Disk. Structural Parameters. II

The King and the EFF (Elson, Fall & Freeman 1987) analytical models are employed to determine the structural parameters of star clusters using an 1-D surface brightness profile fitting method. The structural parameters are derived and a catalogue is provided for 51 star cluster candidates from the survey of compact star clusters in the South-West field of the M31 disk performed by Kodaira et al. (2004).

astro-ph↗
arXiv2007

Effect of muon-nuclear inelastic scattering on high-energy atmospheric muon spectrum at large depth underwater

The energy spectra of hadron cascade showers produced by the cosmic ray muons travelling through water as well as the muon energy spectra underwater at the depth up to 4 km are calculated with two models of muon inelastic scattering on nuclei, the recent hybrid model (two-component, 2C) and the well-known generalized ector-meson-dominance model for the comparison. The 2C model involves photonuclear interactions at low and moderate virtualities as well as the hard scattering including the weak neutral current processes. For the muon scattering off nuclei substantial uclear effects, shadowing, nuclear binding and Fermi motion of nucleons are taken into account. It is shown that deep nderwater muon energy spectrum calculated with the 2C model are noticeably distorted at energies above 100 TeV as compared to that obtained with the GVMD model.

astro-ph↗
arXiv2008

1122 Hz rotation of XTE J1739-285 as a probe of quark matter in the interior of the neutron star

The recent discovery of burst oscillation at 1122Hz in the X-ray transient XTE J1739-285 supports the suggestion that it contains a submillisecond pulsar. In our estimations of the enormous dissipation effect in the transition boundary layer between quark matter core and hadron matter envelope, combing the viscosities of bulk mater in previous works, we show that XTE J1739-285 can be uniquely restricted to a quark star masquerading as a neutron star (hybrid star) that contains a pure quark matter or mixed quark-hadron matter core from minimizing gravitational wave radiation (r-mode) instability and Keplerian motion constraints at 1122Hz level through a three-parameters image. Such constraints allow the stellar radii in the range $9{\rm km}\leq R\leq 12{\rm km}$ and the stellar masses in the range $1.2M_\odot\leq M\leq 2.0M_\odot$. It perhaps implies that submillisecond pulsars are just probes of quark matter.

astro-ph↗
arXiv2007

Sunyaev-Zeldovich and Cosmic Microwave Background

Since its original formulation the Sunyaev-Zeldovich (SZ) effect has been recognized as a ``powerful laboratory'' for our comprehension of physical processes in cosmic structures and to derive crucial information on some general properties of the universe. After a discussion of the fundamental concepts and of some well established applications of the SZ effect towards galaxy clusters, I will focus on dedicated themes related to the SZ effect and other features in the cosmic microwave background (CMB) of particular interest in the view of the extremely high angular resolution observations achievable in the future with the Square Kilometre Array (SKA). SKA will allow the mapping of the thermal and density structure of clusters of galaxies at radio and centimetre bands with unprecedented resolution and sensitivity and with an extremely accurate control of extragalactic radio source contamination. The signatures from SZ effects and free-free emission at galactic scales and in the intergalactic medium probe the structure evolution at various cosmic times. The detection of these sources and their imaging at the high resolution and sensitivity achievable with SKA will greatly contribute to the comprehension of crucial cosmological and astrophysical aspects, as the physical conditions of early ionized halos, quasars and proto-galactic gas. The spectacular improvement in our understanding of the properties of extragalactic radio sources at very faint fluxes achievable with SKA will allow to accurately model their contribution to the diffuse radio background, greatly contributing to the interpretation of next generation of CMB spectrum experiments devoted to probe the thermal plasma history at early times.

astro-ph↗
arXiv2007

Status and Results from AMANDA/IceCube

IceCube is a cubic kilometer-scale neutrino telescope under construction at the South Pole since the austral summer 2004/2005. At the moment it is taking data with 22 deployed strings. The full detector is expected to be completed in 2011 with up to 80 strings each holding 60 digital optical modules. The progenitor detector AMANDA has been operating at the same site since 1997 and is still running as an integral part of IceCube. A summary of AMANDA science for its 10 years of standalone operations is presented, as well as the status and first physics results of the IceCube project.

astro-ph↗
arXiv2007

SOLIS Vector Spectromagnetograph: status and science

The Vector Spectromagnetograph (VSM) instrument has been recording photospheric and chromospheric magnetograms daily since August 2003. Full-disk photospheric vector magnetograms are observed at least weekly and, since November 2006, area-scans of active regions daily. Quick-look vector magnetic images, plus X3D and FITS formated files, are now publicly available daily. In the near future, Milne-Eddington inversion parameter data will also be available and a typical observing day will include three full-disk photospheric vector magnetograms. Besides full-disk observations, the VSM is capable of high temporal cadence area-scans of both the photosphere and chromosphere. Carrington rotation and daily synoptic maps are also available from the photospheric magnetograms and coronal hole estimate images.

astro-ph↗
arXiv2007

String-Like Electrostatic Interaction from QED with Infinite Magnetic Field

In the limit of infinite external magnetic field B the static field of an electric charge is squeezed into a string parallel to B. Near the charge the potential grows like |x_3|(ln |x_3| + const) with the coordinate x_3 along the string. The energy of the string breaking is finite and very close to the effective photon mass.

hep-th↗
arXiv2008

Minimal gauge inflation

We consider a gauge inflation model in the simplest orbifold M4 x S1/Z2 with the minimal non-Abelian SU(2) hidden sector gauge symmetry. The inflaton potential is fully radiatively generated solely by gauge self-interactions. Following the virtue of gauge inflation idea, the inflaton, a part of the five dimensional gauge boson, is automatically protected by the gauge symmetry and its potential is stable against quantum corrections. We show that the model perfectly fits the recent cosmological observations, including the recent WMAP 5-year data, in a wide range of the model parameters. In the perturbative regime of gauge interactions (g_{4D} <= 1/(2pi R M_P)) with the moderately compactified radius (10 <= R M_P <= 100) the anticipated magnitude of the curvature perturbation power spectrum and the value of the corresponding spectral index are in perfect agreement with the recent observations. The model also predicts a large fraction of the gravitational waves, negligible non-Gaussianity, and high enough reheating temperature.

hep-ph↗
arXiv2008

An evolution of the IR-Radio correlation?

Using extremely deep (rms 3.3 microJy/bm) 1.4GHz sub-arcsecond resolution MERLIN + VLA radio observations of a 8'.5 by 8'.5 field centred upon the Hubble Deep Field North, in conjunction with Spitzer 24 micron data we present an investigation of the radio-MIR correlation at very low flux densities. By stacking individual sources within these data we are able to extend the MIR-radio correlation to the extremely faint (~microJy and even sub-microJy) radio source population. Tentatively we demonstrate a small deviation from the correlation for the faintest MIR sources. We suggest that this small observed change in the gradient of the correlation is the result of a suppression of the MIR emission in faint star-forming galaxies. This deviation potentially has significant implications for using either the MIR or non-thermal radio emission as a star-formation tracer at low luminosities.

astro-ph↗