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International Workshop on From Quantum to Cosmos : Fundamental Physics Research in Space
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Gravitational lensing for interstellar power transmission
Get PDFWe investigate light propagation in the gravitational field of multiple
gravitational lenses. Assuming these lenses are sufficiently spaced to prevent
interaction, we consider a linear alignment for the transmitter, lenses, and
receiver. Remarkably, in this axially-symmetric configuration, we can solve the
relevant diffraction integrals -- result that offers valuable analytical
insights. We show that the point-spread function (PSF) is affected by the
number of lenses in the system. Even a single lens is useful for transmission
either it is used as a part of the transmitter or it acts on the receiver's
side. We show that power transmission via a pair of lenses benefits from light
amplification on both ends of the link. The second lens plays an important role
by focusing the signal to a much tighter spot; but in practical lensing
scenarios, that lens changes the structure of the PSF on scales much smaller
than the telescope, so that additional gain due to the presence of the second
lens is independent of its properties and is govern solely by the transmission
geometry. While evaluating the signal-to-noise ratio (SNR) in various
transmitting scenarios, we see that a single-lens transmission performs on par
with a pair of lenses. The fact that the second lens amplifies the brightness
of the first one, creates a challenging background for signal reception.
Nevertheless, in all the cases considered here, we have found
practically-relevant SNR values. As a result, we were able to demonstrate the
feasibility of establishing interstellar power transmission links relying on
gravitational lensing - a finding with profound implications for applications
targeting interstellar power transmission.Comment: 20 pages, 4 figure
Relativistic Navigation: A Theoretical Foundation
Get PDFWe present a theoretical foundation for relativistic astronomical measurements in curved space-time. In particular, we discuss a new iterative approach for describing the dynamics of an isolated astronomical N-body system in metric theories of gravity. To do this, we generalize the Fock-Chandrasekhar method of the weak-field and slow-motion approximation (WFSMA) and develop a theory of relativistic reference frames (RF's) for a gravitationally bounded many-extended-body problem. In any proper RF constructed in the immediate vicinity of an arbitrary body, the N-body solutions of the gravitational field equations are formally presented as a sum of the Riemann-flat inertial space-time, the gravitational field generated by the body itself, the unperturbed solutions for each body in the system transformed to the coordinates of this proper RF, and the gravitational interaction term. We develop the basic concept of a general WFSMA theory of the celestial RF's applicable to a wide class of metric theories of gravity and an arbitrary model of matter distribution. We apply the proposed method to general relativity. Celestial bodies are described using a perfect fluid model; as such, they possess any number of internal mass and current multipole moments that explicitly characterize their internal structures. The obtained relativistic corrections to the geodetic equations of motion arise because of a coupling of the bodies' multiple moments to the surrounding gravitational field. The resulting relativistic transformations between the different RF's extend the Poincare group to the motion of deformable self-gravitating bodies. Within the present accuracy of astronomical measurements we discuss the properties of the Fermi-normal-like proper RF that is defined in the immediate vicinity of the extended compact bodies. We further generalize the proposed approximation method and include two Eddington parameters (gamma, Beta). This generalized approach was used to derive the relativistic equations of satellite motion in the vicinity of the extended bodies. Anticipating improvements in radio and laser tracking technologies over the next few decades, we apply this method to spacecraft orbit determination. We emphasize the number of feasible relativistic gravity tests that may be performed within the context of the parameterized WFSMA. Based on the planeto-centric equations of motion of a spacecraft around the planet, we suggested a new null test of the Strong Equivalence Principle (SEP). The experiment to measure the corresponding SEP violation effect could be performed with the future Mercury Orbiter mission. We discuss other relativistic effects, including the perihelion advance and the redshift and geodetic precession of the orbiter's orbital plane about Mercury, as well as the possible future implementation of the proposed formalism in software codes developed for solar-system orbit determination. All the important calculations are completely documented, and the references contain an extensive list of cited literature
Search for gravitationally lensed interstellar transmissions
Get PDFWe explore interstellar light transmission facilitated by gravitational lensing, focusing on axially-symmetric lensing configurations where the transmitter, lens, and receiver are nearly aligned. Positioning an optical transmitter in the lens\u27s focal region, we investigate the caustic formed by a diffraction-limited annular beam of light emitted by the transmitter. We analyze the impact of the lens\u27s point spread function (PSF) on the projected beam\u27s structure, estimate the power delivered to a receiver at interstellar distances, and assess the major noise sources. We determine detection sensitivity in both noise- and signal-dominated regimes. Considering realistic assumptions about the transmitter\u27s performance, we explore signal detection strategies enhanced by the spatial broadening of the received beam, a result of the transmitting lens\u27s PSF. Our findings indicate that detecting lensed optical signals from nearby stars is achievable using established optical engineering technologies. A network of spatially distributed astronomical facilities capable of observations in multiple narrow spectral bands will enhance the search. Our results support the feasibility of interstellar power transmission via gravitational lensing, directly contributing to ongoing optical SETI efforts.13 pages, 3 figure
The Effect of Companions on the SIM Reference Frame
Get PDFThe Space Interferometry Mission (SIM) is a 10-m Michelson space-based optical interferometer designed for precision astrometry (4 microarcseconds, 3 microarcseconds/year) with better accuracy than before over a narrow field of view. One of the primary objectives of the SIM instrument is to determine accurately the directions to a grid of stars, together with their proper motions and parallax, improving a priori knowledge by nearly three orders of magnitude over Hipparcos and one order of magnitude over FAME's planned accuracy (Johnston, 2000). The instrument does not measure directly the angular separation between stars, but rather it measures the projection of each star's direction vector onto the interferometer baseline vector by measuring the pathlength delay of starlight as it passes through the two arms of the interferometer. The accuracy and stability of SIM's celestial reference frame is subject to degradation over the 5-year mission from the reflex motion induced by massive companions of the objects used to construct the celestial reference frame. The authors present the results of simulations that show the sensitivity of reference frame accuracy to companions as a function of mass and period. They assume that pre-launch ground surveys will eliminate all objects with RMS radial velocity greater than 10 m/s. They further assume that the standard astrometric parameters of position, parallax, and proper motion plus acceleration terms in right ascension and declination will be allowed to absorb reflex motion
Observational Model for Precision Astrometry with the Space Interferometry Mission
Get PDFThe Space Interferometry Mission (SIM) is a space-based 10-m baseline Michelson optical interferometer operating in the visible waveband that is designed to achieve astrometric accuracy in the single digits of the microarcsecond domain. Over a narrow field of view SIM is expected to achieve a mission accuracy of 1 microarcsecond. In this mode SIM will search for planetary companions to nearby stars by detecting the astrometric "wobble" relative to a nearby reference star. In its wide-angle mode, SIM will provide 4 microarcsecond precision absolute position measurements of stars, with parallaxes to comparable accuracy, at the end of its 5-year mission. The expected proper motion accuracy is around 3 microarcsecond/year, corresponding to a transverse velocity of 10 m/ s at a distance of 1 kpc. The basic astrometric observable of the SIM instrument is the pathlength delay. This measurement is made by a combination of internal metrology measurements that determine the distance the starlight travels through the two arms of the interferometer, and a measurement of the white light stellar fringe to find the point of equal pathlength. Because this operation requires a non-negligible integration time, the interferometer baseline vector is not stationary over this time period, as its absolute length and orientation are time varying. This paper addresses how the time varying baseline can be "regularized" so that it may act as a single baseline vector for multiple stars, as required for the solution of the astrometric equations
Recovering the mass distribution of an extended gravitational lens
Get PDFWe investigate the possibility of determining the mass distribution of a
gravitational lens via lensing observations. We consider an extended, compact
gravitational lens, representing its static external gravitational potential
via an infinite set of symmetric trace free (STF) multipole moments. Within the
wave-optical treatment, we evaluate the caustics formed in the lens's point
spread function (PSF). We study the only quantity that is available in
astronomical lensing observations: the image of that PSF formed by an imaging
telescope. This observable may be used to recover some physical characteristics
of the lens, including its shape, orientation and composition. Illustrating
this, we study exotic gravitational lenses formed by several well-known solids
with uniform density. We show that when moments beyond the quadrupole are
observed, some of the symmetry properties of the lens can be recovered. The
presence of an octupole moment implies breaking the "north-south" symmetry of
the mass distribution in the lens. The presence of a rotated hexadecapole
moment implies breaking axial symmetry. As such, if observations of lensed
images allow the reconstruction of these moments, important information about
the mass distribution and dynamics of the lens can be obtained. This may help
with choosing the most appropriate mass profile that is used to characterize
the mass distribution of astrophysical lenses, such as the dark matter halos
that are presumed to contain most of the mass of galaxies and clusters of
galaxies. Our results are novel and offer new insight into gravitational
lensing by realistic astrophysical systems.Comment: 21 pages, 11 figures, 1 tabl
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