Seventeenth Marcel Grossmann Meeting

Session

Gravitational lensing, shadows and photon rings

EG2

8 Jul 2024, 15:00

Aurum, the ‘Gabriele d’Annunzio’ University and ICRANet

Conveners

Gravitational lensing, shadows and photon rings: Monday block 1

• Oleg Tsupko (ZARM, Bremen University, Germany)
• Volker Perlick

Gravitational lensing, shadows and photon rings: Monday block 2

• Oleg Tsupko (ZARM, Bremen University, Germany)
• Volker Perlick

Gravitational lensing, shadows and photon rings: Friday block 1

• Oleg Tsupko (ZARM, Bremen University, Germany)
• Volker Perlick

Gravitational lensing, shadows and photon rings: Friday block 2

• Volker Perlick
• Oleg Tsupko (ZARM, Bremen University, Germany)

Description

This session is devoted to gravitational lensing, shadows and photon rings. Emphasis is expected to be on analytical and numerical studies. In particular, we will discuss the shadows of black holes and other compact objects, higher-order images produced by lensing and the influence of a plasma on lensing effects. Talks on other aspects of light propagation in gravitational fields are welcome as well.

533. Light bending around a gravitating object immersed in a moving medium

Barbora Bezdekova (Charles University)

08/07/2024, 15:00

Gravitational lensing, shadows and photon rings

Invited talk in a parallel session

A well-known effect confirmed by astrophysical observations is the light deflection in the gravitational field. In the recent years, the Hamiltonian formalism has been frequently applied in analytical studies to discuss how a medium that surrounds the gravitating object changes the light bending compared to the absence of the medium. Within this formalism, the medium is usually regarded as a...

401. Gravitational lensing by wormholes

Volker Perlick

08/07/2024, 15:25

Gravitational lensing, shadows and photon rings

Talk in a parallel session

In this talk I consider the propagation of light rays, either in vacuum or in a non-magnetised pressure-less plasma, in axially symmetric and stationary spacetimes that describe wormholes. Among other things, I discuss the necessary and sufficient conditions for separability of the Hamilton-Jacobi equation (i.e., for the existence of a Carter constant) which allows complete integrability. For...

314. Shadows of supermassive dark compact objects at galaxy centers

Carlos Raúl Argüelles (Universidad Nacional de La Plata)

08/07/2024, 15:50

Gravitational lensing, shadows and photon rings

Talk in a parallel session

Current images of the supermassive black hole (SMBH) candidates observed at the center of our Galaxy and M87, have opened an unprecedented era to study both, gravity in its strong regime and the very nature of the relativistic sources. Very-long-baseline interferometry (VLBI) data show images consistent with a central black hole as predicted by General Relativity (GR). However, it is important...

301. Shape of higher-order photon rings in image of Schwarzschild black hole

Oleg Tsupko (ZARM, Bremen University, Germany)

08/07/2024, 17:00

Gravitational lensing, shadows and photon rings

Talk in a parallel session

Higher-order photon rings can be expected to be detected in a more detailed image of the black hole found in future observations. These rings are lensed images of the luminous matter surrounding the black hole and are formed by photons that loop around it. We have succeeded to derive an analytical expression for the shape of the higher-order rings in the form that is most convenient for...

90. Constraining spherically symmetric metrics by the gap between photon rings

Fabio Aratore (Università degli studi di Salerno)

08/07/2024, 17:25

Gravitational lensing, shadows and photon rings

Talk in a parallel session

Gravitational lensing of luminous matter that surrounds a black hole or some other sufficiently compact object produces an infinite sequence of images. Besides the direct (or primary) image, it comprises demagnified and deformed replicas of the original known as photon rings which are progressively nearing the boundary of the socalled shadow.
We present analytical approximation formulas for...

449. Gravitational Lensing in the Kerr Spacetime: The Standard Observer

Torben Frost (Kavli Institute for Astronomy and Astrophysics - Peking University)

08/07/2024, 17:50

Gravitational lensing, shadows and photon rings

Talk in a parallel session

The Kerr spacetime is one of the most relevant spacetimes in contemporary astrophysics and describes the spacetime of a rotating black hole. When light rays pass by or are emitted in the close vicinity of a Kerr black hole they are gravitationally lensed and this leads to characteristic lensing features on the sky of a distant observer. While it is a common assumption that the observer is...

511. Extended source effect with thin light bundles

Dr Nezihe Uzun (Polish Academy of Sciences, Center for Theoretical Physics)

12/07/2024, 15:00

Gravitational lensing, shadows and photon rings

Invited talk in a parallel session

Geometric optics limit is considered to be a good-enough approximation for the calculation of distances and image distortions in curved spacetime. It is usually assumed that spherical waves are emitted from a point source and we observe a section of the wavefront. In the geometric optics limit, this section is represented by a thin bundle of rays. Accordingly, the intensity profile on the...

163. A seven Parameter Kerr-Newman-like Metric

Francisco Frutos-Alfaro (Escuela de Fisica, Universidad de Costa Rica)

12/07/2024, 15:25

Gravitational lensing, shadows and photon rings

Talk in a parallel session

In this contribution a new metric with seven parameters is found.
The metric possess the following features: mass, rotation, charge,
magnetic dipole, massive quadrupole, octupole, and hexadecapole.
These spacetime is versatile and realistic for representing compact objects like neutron stars. It has several astrophysical applications, for
example to study the chaotic behavior of geodesics...

305. The Optical Appearance of a Black Hole

Mr Muhammad Ali Raza (COMSATS University Islamabad, Lahore Campus)

12/07/2024, 15:50

Gravitational lensing, shadows and photon rings

Talk in a parallel session

Since the first theoretical proposition of a black hole solution, it has been one of the most investigated questions that what would be the appearance of a black hole. There have been hundreds of black hole solutions in various frameworks for which studies are available dealing with the optical images of these black hole models. Currently, we call it the black hole shadow as it turns out due...

215. Polarized image of equatorial emission in horizonless spacetimes

Valentin Deliyski (Sofia University "st. Kliment Ohridski")

12/07/2024, 17:00

Gravitational lensing, shadows and photon rings

Talk in a parallel session

We study the linear polarization from the accretion disk around horizonless compact objects. Previous works have shown that these spacetimes can have significantly different lensing properties from black holes. In particular, their relativistic images can exibit a qualitatively new ring structure, inside what would be the shadow region. We search for characteristic signatures which could...

148. Shadows of rotating hairy Kerr black holes coupled to time periodic scalar fields with a nonflat target space”

Dr Galin Gyulchev (Sofia University "St. Kliment Ohridski")

12/07/2024, 17:25

Gravitational lensing, shadows and photon rings

Talk in a parallel session

We study the shadows cast by rotating hairy black holes with two non-trivial time-periodic scalar fields having a non-flat Gaussian curvature of the target space spanned by the scalar fields. Such black holes are a viable alternative to the Kerr black hole, having a much more complicated geodesic structure and resulting shadows. We investigate how a nontrivial Gauss curvature alters the...

111. Semiclassical lensing and Radiative Lense Equations

claudio coriano (Universita del Salento)

12/07/2024, 17:50

Gravitational lensing, shadows and photon rings

Talk in a parallel session

We present phenomenological analysis of photon lensing in an external gravitational background in the case of photons and neutrinos, and propose a method to incorporate radiative effects in the classical lens equations. The study is performed for a Schwarzschild metric, generated by a point-like source, and expanded in the Newtonian potential at first order. We use a semiclassical approach,...

476. Can relativistic effects explain galactic dynamics without dark matter?

Filipe Costa (CAMGSD - Instituto Superior Técnico, Universidade de Lisboa)

Gravitational lensing, shadows and photon rings

Talk in a parallel session

In a growing number of recent works, it has been claimed that "gravitomagnetism"/frame-dragging and/or non-linear general relativistic effects can play a leading role in galactic dynamics, partially or totally replacing dark matter. Using the 1+3 "quasi-Maxwell" formalism (and generalizing it for null geodesics), we show, on general grounds, such hypothesis to be impossible. We demonstrate...

204. Geometry of trapped photon region in the phase space of Kerr-Newman and Kerr-Sen spacetime

Karim Mosani (Ruhr University (Bochum), Germany)

Gravitational lensing, shadows and photon rings

Talk in a parallel session

In Einstein’s general relativity, extremely strong gravity can trap light. In a spacetime admitting a singularity, we say that light (or a “photon”) is trapped if it neither escapes to spatial infinity nor falls into the singularity. Null geodesics govern the trajectories of light. In the Schwarzschild spacetime with positive mass $M$, there exist (unstable) circular orbits of trapped photons...

378. Least model-dependent strong lensing properties of galaxy clusters

Jenny Wagner (Bahamas Advanced Study Institute and Conferences)

Gravitational lensing, shadows and photon rings

Invited talk in a parallel session

Strong gravitational lenses are massive cosmic objects, like galaxies or galaxy clusters, which can map an extended background source, like a galaxy, into several highly distorted and magnified images. Analysing the properties of those images yields important information about the distribution of the deflecting mass and the background source. Common approaches to reconstruct the source or the...