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Universe
Special Issues
Gravitational Lensing and Astrometry
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Gravitational Lensing and Astrometry

A special issue of Universe (ISSN 2218-1997).

Deadline for manuscript submissions: closed (31 October 2017) | Viewed by 24939

Special Issue Editors

Dr. Valerio Bozza

E-Mail Website
Guest Editor
Dipartimento di Fisica "E.R. Caianiello", Università di Salerno, Via Giovanni Paolo II 132, I-84084 Fisciano, Italy
Interests: gravitational lensing; relativistic astrophysics; extrasolar planets
Dr. Francesco De Paolis

E-Mail Website
Guest Editor
1. Dipartimento di Matematica e Fisica “Ennio De Giorgi”, Università del Salento, CP 193, I-73100 Lecce, Italy
2. INFN, Sezione di Lecce, Via per Arnesano, I-73100 Lecce, Italy
Interests: gravitational lensing; relativistic astrophysics
Special Issues, Collections and Topics in MDPI journals
Dr. Achille A. Nucita

E-Mail Website
Guest Editor
Dipartimento di Matematica e Fisica “Ennio De Giorgi”, Università del Salento, CP 193, I-73100 Lecce, Italy
Interests: gravitational lensing; relativistic astrophysics

Special Issue Information

Dear Colleagues,

Albert Einstein's General Theory of Relativity, which celebrates the centenary in 2016, opened up many new windows on our comprehension of the Universe. One of these windows is represented by gravitational lensing, which is still an extremely powerful method of investigation in astrophysics and cosmology: It is adopted to study the distribution of the stellar component in the Milky Way and other galaxies, to study dark matter and dark energy on very large scales, to discover exoplanets, and there are perspectives to measure the physical parameters of supermassive black holes in galaxy cores. In all these achievements, astrometric measurements are playing a major role. Thanks to technological advancement, and in particular the launch of the GAIA space telescope, astrometry will allow scientists to achieve a three-dimensional map of the Milky Way and to measure the distance and proper motion of more than ten billions stars with unprecedented precision. Meanwhile, interferometry in radio and infrared bands are in rapid development, and more spacecraft are planned to conduct wide-field surveys in which astrometry and gravitational lensing will find new synergies, reaching the ability to probe strong lensing effects around the black hole in the center of the Milky Way. In extragalactic lensing, astrometry is essential for accurate reconstruction of mass distribution in galaxy halos and clusters and to ultimately constrain the nature of dark matter.

Dr. Valerio Bozza
Dr. Francesco De Paolis
Dr. Achille A. Nucita
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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Published Papers (5 papers)

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Research

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17 pages, 7680 KiB  
Article
Accurate Mass Measurements for Planetary Microlensing Events Using High Angular Resolution Observations
by Jean-Philippe Beaulieu
Universe 2018, 4(4), 61; https://doi.org/10.3390/universe4040061 - 24 Apr 2018
Cited by 10 | Viewed by 3661
Abstract
The microlensing technique is a unique method to hunt for cold planets over a range of mass and separation, orbiting all varieties of host stars in the disk of our galaxy. It provides precise mass-ratio and projected separations in units of the Einstein [...] Read more.
The microlensing technique is a unique method to hunt for cold planets over a range of mass and separation, orbiting all varieties of host stars in the disk of our galaxy. It provides precise mass-ratio and projected separations in units of the Einstein ring radius. In order to obtain the physical parameters (mass, distance, orbital separation) of the system, it is necessary to combine the result of light curve modeling with lens mass-distance relations and/or perform a Bayesian analysis with a galactic model. A first mass-distance relation could be obtained from a constraint on the Einstein ring radius if the crossing time of the source over the caustic is measured. It could then be supplemented by secondary constraints such as parallax measurements, ideally by using coinciding ground and space-born observations. These are still subject to degeneracies, like the orbital motion of the lens. A third mass-distance relation can be obtained thanks to constraints on the lens luminosity using high angular resolution observations with 8 m class telescopes or the Hubble Space Telescope. The latter route, although quite inexpensive in telescope time is very effective. If we have to rely heavily on Bayesian analysis and limited constraints on mass-distance relations, the physical parameters are determined to 30–40% typically. In a handful of cases, ground-space parallax is a powerful route to get stronger constraint on masses. High angular resolution observations will be able to constrain the luminosity of the lenses in the majority of the cases, and in favorable circumstances it is possible to derive physical parameters to 10% or better. Moreover, these constraints will be obtained in most of the planets to be discovered by the Euclid and WFIRST satellites. We describe here the state-of-the-art approaches to measure lens masses and distances with an emphasis on high angular resolution observations. We will discuss the challenges, recent results and perspectives. Full article
(This article belongs to the Special Issue Gravitational Lensing and Astrometry)
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11548 KiB  
Article
Gravitational Lensing in Presence of Plasma: Strong Lens Systems, Black Hole Lensing and Shadow
by Gennady S. Bisnovatyi-Kogan and Oleg Yu. Tsupko
Universe 2017, 3(3), 57; https://doi.org/10.3390/universe3030057 - 17 Jul 2017
Cited by 99 | Viewed by 9769
Abstract
In this article, we present an overview of the new developments in problems of the plasma influence on the effects of gravitational lensing, complemented by pieces of new material and relevant discussions. Deflection of light in the presence of gravity and plasma is [...] Read more.
In this article, we present an overview of the new developments in problems of the plasma influence on the effects of gravitational lensing, complemented by pieces of new material and relevant discussions. Deflection of light in the presence of gravity and plasma is determined by a complex combination of various physical phenomena: gravity, dispersion, refraction. In particular, the gravitational deflection itself, in a homogeneous plasma without refraction, differs from the vacuum one and depends on the frequency of the photon. In an inhomogeneous plasma, chromatic refraction also takes place. We describe chromatic effects in strong lens systems including a shift of angular position of image and a change in magnification. We also investigate high-order images that arise when lensing on a black hole surrounded by homogeneous plasma. The recent results of analytical studies of the effect of plasma on the shadow of the Schwarzschild and Kerr black holes are presented. Full article
(This article belongs to the Special Issue Gravitational Lensing and Astrometry)
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226 KiB  
Article
Etherington’s Distance Duality with Birefringence
by Frederic P. Schuller and Marcus C. Werner
Universe 2017, 3(3), 52; https://doi.org/10.3390/universe3030052 - 6 Jul 2017
Cited by 11 | Viewed by 2948
Abstract
We consider light propagation in a spacetime whose kinematics allow weak birefringence, and whose dynamics have recently been derived by gravitational closure. Revisiting the definitions of luminosity and angular diameter distances in this setting, we present a modification of the Etherington distance duality [...] Read more.
We consider light propagation in a spacetime whose kinematics allow weak birefringence, and whose dynamics have recently been derived by gravitational closure. Revisiting the definitions of luminosity and angular diameter distances in this setting, we present a modification of the Etherington distance duality relation in a weak gravitational field around a point mass. This provides the first concrete example of how the non-metricities implied by gravitational closure of birefringent electrodynamics affect observationally testable relations. Full article
(This article belongs to the Special Issue Gravitational Lensing and Astrometry)
1004 KiB  
Article
Gravitational Lensing of Rays through the Levitating Atmospheres of Compact Objects
by Adam Rogers
Universe 2017, 3(1), 3; https://doi.org/10.3390/universe3010003 - 1 Jan 2017
Cited by 32 | Viewed by 3639
Abstract
Electromagnetic rays travel on curved paths under the influence of gravity. When a dispersive optical medium is included, these trajectories are frequency-dependent. In this work we consider the behaviour of rays when a spherically symmetric, luminous compact object described by the Schwarzschild metric [...] Read more.
Electromagnetic rays travel on curved paths under the influence of gravity. When a dispersive optical medium is included, these trajectories are frequency-dependent. In this work we consider the behaviour of rays when a spherically symmetric, luminous compact object described by the Schwarzschild metric is surrounded by an optically thin shell of plasma supported by radiation pressure. Such levitating atmospheres occupy a position of stable radial equilibrium, where radiative flux and gravitational effects are balanced. Using general relativity and an inhomogeneous plasma we find the existence of a stable circular orbit within the atmospheric shell for low-frequency rays. We explore families of bound orbits that exist between the shell and the compact object, and identify sets of novel periodic orbits. Finally, we examine conditions necessary for the trapping and escape of low-frequency radiation. Full article
(This article belongs to the Special Issue Gravitational Lensing and Astrometry)
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Review

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618 KiB  
Review
Microlensing and Its Degeneracy Breakers: Parallax, Finite Source, High-Resolution Imaging, and Astrometry
by Chien-Hsiu Lee
Universe 2017, 3(3), 53; https://doi.org/10.3390/universe3030053 - 7 Jul 2017
Cited by 7 | Viewed by 3809
Abstract
First proposed by Paczynski in 1986, microlensing has been instrumental in the search for compact dark matter as well as discovery and characterization of exoplanets. In this article, we provide a brief history of microlensing, especially on the discoveries of compact objects and [...] Read more.
First proposed by Paczynski in 1986, microlensing has been instrumental in the search for compact dark matter as well as discovery and characterization of exoplanets. In this article, we provide a brief history of microlensing, especially on the discoveries of compact objects and exoplanets. We then review the basics of microlensing and how astrometry can help break the degeneracy, providing a more robust determination of the nature of the microlensing events. We also outline prospects that will be made by on-going and forth-coming experiments/observatories. Full article
(This article belongs to the Special Issue Gravitational Lensing and Astrometry)
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