33 research outputs found
Detection of compact objects by means of gravitational lensing in binary systems
We consider the gravitational magnification of light for binary systems
containing two compact objects: white dwarfs, a white dwarf and a neutron star
or a white dwarf and a black hole. Light curves of the flares of the white
dwarf caused by this effect were built in analytical approximations and by
means of numerical calculations. We estimate the probability of the detection
of these events in our Galaxy for different types of binaries and show that
gravitational lensing provides a tool for detecting such systems. We propose to
use the facilities of the Sloan Digital Sky Survey (SDSS) to search for these
flares. It is possible to detect several dozens compact object pairs in such a
programme over 5 years. This programme is apparently the best way to detect
stellar mass black holes with open event horizons.Comment: 15 pages, 11 figures; Accepted for publication in Astronomy &
Astrophysic
Using microlensed quasars to probe the structure of the Milky Way
This paper presents an investigation into the gravitational microlensing of
quasars by stars and stellar remnants in the Milky Way. We present predictions
for the all-sky microlensing optical depth, time-scale distributions and event
rates for future large-area sky surveys. As expected, the total event rate
increases rapidly with increasing magnitude limit, reflecting the fact that the
number density of quasars is a steep function of magnitude. Surveys such as
Pan-STARRS and LSST should be able to detect more than ten events per year,
with typical event durations of around one month. Since microlensing of quasar
sources suffers from fewer degeneracies than lensing of Milky Way sources, they
could be used as a powerful tool for recovering the mass of the lensing object
in a robust, often model-independent, manner. As a consequence, for a subset of
these events it will be possible to directly `weigh' the star (or stellar
remnant) that is causing the lensing signal, either through higher order
microlensing effects and/or high-precision astrometric observations of the lens
star (using, for example, Gaia or SIM-lite). This means that such events could
play a crucial role in stellar astronomy. Given the current operational
timelines for Pan-STARRS and LSST, by the end of the decade they could
potentially detect up to 100 events. Although this is still too few events to
place detailed constraints on Galactic models, consistency checks can be
carried out and such samples could lead to exciting and unexpected discoveries.Comment: 11 pages, 8 figures. MNRAS (in press). Minor revisions according to
referee's report; mainly presentational issues and clarification of a few
items in the discussion; results and conclusions remain unchange
Scattering of gravitational radiation
Aims.The effect of gravitational microlensing on the intensity of gravitational radiation as it propagates through an inhomogeneous medium is considered. Lensing by both stars and a power law spectrum of density perturbations is examined.
Methods.The long wavelengths characteristic of gravitational radiation mandate a statistical, physical-optics approach to treat the effect of the lensing.
Results.A model for the mass power spectrum of a starfield, including the effects of clustering and allowing for a distribution of stellar masses, is constructed and used to determine both the amplitude of fluctuations in the gravitational wave strain and its associated temporal fluctuation spectrum. For a uniformly distributed starfield the intensity variance scales linearly with stellar density, σ, but is enhanced by a factor \ga when clustering is important, where rF is the Fresnel scale. The effect of lensing by a power law mass spectrum, applicable to lensing by small scale fluctuations in gas and dark matter, is also considered.
For power law mass density spectra with indices steeper than -2 the wave amplitude exhibits rms fluctuations %, where is the variance in the mass surface density measured in and Deff is the effective distance to the lensing medium. For shallower spectra the amplitude of the fluctuations depends additionally on the inner length scale and power law index of the density fluctuations. The intensity fluctuations are dominated by temporal fluctuations on long timescales. For lensing material moving at a speed v across the line of sight the fluctuation timescale exceeds . Lensing by small scale structure induces at most ≈15% rms variations if the line of sight to a gravitational wave source intersects a region with densities ~, which are typically encountered in the vicinity of galaxy clusters
Notes on Hidden Mirror World
A few remarks on Dark Matter (DM) models are presented. An example is Mirror
Matter which is the oldest but still viable DM candidate, perhaps not in the
purest form. It can serve as a test-bench for other analogous DM models, since
the properties of macroscopic objects are quite firmly fixed for Mirror Matter.
A pedagogical derivation of virial theorem is given and it is pointed out that
concepts of virial velocity or virial temperature are misleading for some
cases. It is shown that the limits on self-interaction cross-sections derived
from observations of colliding clusters of galaxies are not real limits for
individual particles if they form macroscopic bodies. The effect of the heating
of interstellar medium by Mirror Matter compact stars is very weak but may be
observable. The effect of neutron star heating by accretion of M-baryons may be
negligible. Problems of MACHOs as Mirror Matter stars are touched upon.Comment: Latex, revtex, 24 pages, 1 figure, references updated and adde