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Questions tagged [gravitational-lensing]

Gravitational lensing occurs when light from a distant object is bent as it travels to an observer, due to passing through the gravitational field of a massive object (such as a galaxy, or black hole).

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Gravitational Lensing: Up, Down or Sideways

I have been reading about Eddington and his measurement of 1.75 arc seconds in 1919. What I am wondering is why was the measurement lateral? I picture a beam of star light entering a curvature of ...
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Superradiant scattering in ergosphere?

In a black hole there is a region of space where only energy can escape, the ergosphere. I read superradiant scattering can allow lights to gain energy much like gravity assist, what is the different ...
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Propagation of gravitaional waves near black holes [duplicate]

As we know near black holes light gets strongly deflected. And if the gravity of the black hole is strong enough, the light can move in circles around the black hole. How the gravitational wave ...
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Flattening a curved space

It is possible, apparently, to describe gravitational lensing as if gravitational potential induces an effective refractive index change in the vacuum, and spacetime is flat. As pointed out by @...
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Gravitational potential, effective refractive index, and vacuum charge density

In an earlier question, I asked about how to explain gravitational lensing to a layman in terms of propagating wave fronts, in a way analogous to the way an optical lens can be explained: the ...
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How to explain gravitational lensing to a layman?

This question is about how to explain gravitational lensing to a layman, not about exact theoretical correctness. I am accustomed to explaining optical refraction in terms of wavefronts and the fact ...
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Can gravitational lensing also applied to gravitational wave?

We know light travels in a straight line but spacetime around an object with mass is curved, anyhow I'm wondering gravitational wave going at speed of light could also be bended by stars and probably ...
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Is gravitational lensing affected by dark energy?

Is gravitational lensing affected by dark energy? I mean, despite the effect if cause on the expanding Universe, could dark energy cause gravitational or anti-gravitational lensing?
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Does the Sun cause star to appear in the sky on two different positions?

So, I was reading A brief history of time and it was talking about the sun bending the light of a star causing it to appear on a different place from where it actually was located. I was wondering if ...
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Gravitational Lenses in External Shear Fields

I am reading Massimo Meneghetti's notes on gravitational lenses, available here: http://www.ita.uni-heidelberg.de/~massimo/sub/Lectures/gl_all.pdf On page 38 he begins discussing embedding a lens in ...
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Could you actually see the event horizon of a Black Hole?

For years I thought to myself that surely you'd be able to see the event horizon of a Black Hole when looking at it against the surrounding light. I thought that it would be similar to this: Where ...
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Does 'special relativity + newtonian gravity' predict gravitational bending of light?

It seems to me that special relativity (SR) already predicts that gravity will bend light rather than this effect being a proof of general relativity (GR). Photons have energy proportional to their ...
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Is it possible to see the Milky Way galaxy through a gravitational lens? [duplicate]

I have been thinking about these amazing images of ancient galaxies we can see because of gravitational lensing. Some of them even have multiple images of the same galaxy in two different places ...
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Convergence and shear in weak gravitational lensing

When we try to reconstruct the surface mass density distribution of a lens, we can do the following: Divide the picture into a grid, and for each "pixel" assign an effective distortion by finding $g$ ...
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Gravitational lensing of gravity

I have read these questions: Do gravitational lenses work on gravitational waves? Are gravitational waves effected by the curvature of space time (gravitational lensing)? And it made me curious. I ...
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Can the double slit experiment be answered with Einstein's gravitational lensing effect?

Since the original double slit experiment was done over 100 years ago, it probably wasn't done in a vacuum. I've noticed that the Einstein's lensing effect (or something similar) happens by looking ...
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Dark Matter and Gravity

If gravitational lensing implies that Dark Matter exerts gravity onto light then why are the stars and regular matter not clustering around Dark Matter?
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Doubts about gravitational lens magnification

A gravitational lens approximately follows a $1/r$-curve, meaning that rays closer to the lensing object get bent more than those away. My question is, wouldn't that shrink any image as opposed to ...
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What would the sky look like if the Sun was a black hole?

As a complement of this Phys.SE question. What kind of lensing and diffractions effects from space would be perceived on earth?
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why gravitational lensing preserve surface brightness?

Textbook tells me that the gravitational lensing preserve surface brightness due to the Liouville theorem. I don't understand why the Liouville theorem indicate a preservation of surface brightness? ...
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Heuristic formula to compute geodesic deviation for rays close to a galaxy

I'm looking for a way to quickly estimate geodesic deviation of light rays passing close to a galaxy. For simplicity I'm assuming the geodesic is passing through the center of the galaxy and leaving ...
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Observing an event in the past?

I'm writing a Sci Fi novel and I'm trying to come up with a (fairly) realistic or at least vaguely plausible mechanism for this person's ability to exist and function. Hypothetically, would it be ...
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Is there evidence the great attractor isn't just gravitationally lensed gravity?

Is there any evidence that the great attractor isn't just gravitationally lensed gravity? It seems odd that it would be directly on the other side of the black hole at the center of our galaxy and ...
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Magnification associated with axially symmetric gravitational lens

I am reading someone's notes on gravitational lensing, in particular the section on point masses as lenses. In this case the deflection angle is $$\hat{\alpha} = \frac{4GM}{c^2b} = \frac{4GM}{c^2 D_\...
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Integrating a laplacian over $\mathbb{R}^2$ (related to gravitational lensing)

I am reading somebody's notes on gravitational lensing, and I come across the following: \begin{equation} \kappa = \frac{1}{2} \nabla^2_x \Psi \end{equation} \begin{equation} \Rightarrow \Psi ...
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Gravitational waves' path and interaction with black holes

As a gravitational wave propagates away from its source, how does its path get affected if a black hole is in its way? I was trying to picture it visually and here was my 'before' (with the line being ...
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Orbital mechanics of light

So with traditional orbit mechanics, an object coming in from outside a system will follow a hyperbolic path, and have greater speed when closer to the body. But my question is, how exactly does ...
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(How) does gravitational lensing affect red shift?

In all the measurements taken over the years, has anyone ever observed any effect of gravitational lensing on red shift? So: if we would look at 2 galaxies at, say, 250 million lightyears away, where ...
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Gravitational Lensing equivalent refractive index vs. 9 more free variables in GR

Reading about gravitational lensing here and here, its seems that it can be explained well by assuming a refractive index created by a gravitional potential $$n(\vec{x}) = 1+2\frac{\phi(\vec{x})}{c^2}$...
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Is matter - dark matter symmetry possible?

The gravitational lensing evidence suggests massive and relatively dense accumulations of dark matter in space. However, dark matter collapsing to dense regions is unlikely due to energy conservation. ...
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In gravitational lensing, if the source is infinitely far away how can we have an image on the same side of the lens?

In the standard picture of gravitational lensing, we have a picture like the one you can see as Figure 1 of this paper (I don't know if I can copy/paste it). In it, the source S and the observer O are ...
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Gravitational lenses and two slit experiment

When an image of a distant galaxy is split by a gravitational lens are the photons from the two images capable of displaying interference? This may not be possible in real conditions because of ...
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Do we have real photos of gravitational lensing or microlesnsing caused by black holes?

I have seen real photos of gravitational lensing caused by galaxies or Galaxy clusters and I have seen artistic photos of gravitational lensing caused by black holes. But I am not sure if I have ever ...
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Are black holes black or invisible? [duplicate]

This may be a really basic question with the simplest of answers, but as much sense as it makes to think that black holes are not, in fact, black but invisible - because light would be gravitationally ...
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A simple example and explanation of gravitational lensing

I've recently been looking into gravitational lensing for the purpose of creating interesting visual effects through cgi. However, the wikipedia page doesn't go into much detail about the mathematical ...
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Help to understand the derivatiopn of the solution of this equation

Please, help here people. Im reading this article Wave Optics in Gravitational Lensing (T. T. Nakamura, 1999) . In the article start work with \begin{equation} (\nabla ^2 +\omega)\tilde\phi = 4\...
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Could there be a physical explanation for a relatively large tangential shear value at large distances from a galaxy cluster?

Shown here is a plot of a tangential shear profile, generated by stacking the tangential shear profiles of 64 fields of galaxy clusters. The outer distance is about 2.5 times the radius of a cluster ...
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Black holes are transparent?

Are black holes in a sense transparent? Meaning, they don't 'hide' any stars that happen to be 'behind' them? A regular object obviously blocks a point source of light emanating from 'behind' it. ...
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Can something you see through a telescope be behind you?

I read somewhere that gravity is able to bend light. Is there a chance that, if the conditions are right, the light from one star could bend so much through space that when it reaches the telescope ...
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Weak lensing: Can tangential shear be negative?

I am studying the stacked tangential shear profiles of a field of ~30,000 galaxies, with the aim of plotting the tangential shear profiles as a function of distance from the centre of the field. We ...
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Can a (micro) black hole be used to make a microscope?

We have seen that black-holes can be used as a telescope. Is there a chance that light bending from a micro black-hole can be used to create a microscope?
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Gravity will bend light. But will bent/curved light create gravity? [duplicate]

The first bit is well documented. Einstein (and others) supposed that gravity could bend light. We first observed it around the sun at total solar eclipse, and now it is a tool for astronomers and ...
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Gravitation wave lensing [duplicate]

Can black holes act as a lens for gravitational waves? If space-time dips around a black hole or any source of gravity then can the gravitational waves be affected by that?
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Gravitons unaffected by gravitational lensing?

Photons have energy, and so they are affected by gravitational lensing. More generally, they feel the force of gravity. Gravitons have energy too, but it seems preposterous to assume they will swerve ...
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In weak gravitational lensing, how is the magnification of a source the sum of the magnifications of all its images?

From Gravitational Lensing: Strong, Weak and Micro by Schneider, Kochanek and Wambsganss we are told that the images of a small source are magnified by $|\mu(\vec{\theta_i})|$. Then it follows that ...
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Optical distortion caused by a vortex: “gravitational lensing” in a swimming pool?

Falaco solitons were accidentally discovered by professor R. M. Kiehn while he was visiting a friend's swimming pool. He describes them as [...] a pair of globally stabilized rotational ...
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How is the distortion matrix determined in weak gravitational lensing?

Problem For a weak lensing system, with deflection potential $\psi(\theta)$, the distortion matrix is given by $$\vec{A}(\vec{\theta})=\delta_{ij}-\frac{\partial^2\psi}{\partial\theta_i\partial\...
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Treating gravitational lensing as index of refraction

In Einstein's theory of gravity, an electromagnetic wave passing near a massive object is bent from its rectilinear path. We may regard this bending equivalently as due to a medium of refractive index ...
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Derivation of the Poisson equation for weak gravitational lensing

In my BSc project we studied the derivation of deflection potential for a weak lensing system, which is $$\psi(\vec{\theta})=\frac{1}{\pi}\int_{R^2}d^2\theta' \kappa(\vec{\theta'})\ln{|\vec{\theta}-\...
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Help with this geometrical approach to deriving the lens equation for weak lensing

All images and quotations are from Schneider, Kochanek and Wambsganss. Here is an image of a typical weak lensing setup. Since $D_{ds}$ and $D_s$ are much larger than the extent of the lens and ...