# Questions tagged [gravitational-lensing]

Questions regarding the bending of light by mass or energy.

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### Newtonian vs General Relativistic light deflection angle

The Newtonian prediction and GR prediction of light deflection angles are $\frac{2GM}{c^2 R}$ vs. $\frac{4GM}{c^2 R}$. One gives 0.8 arcsec and the other 1.7 arcsec for deflection around the Sun, and ...
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### Light deflection during solar eclipse

On this website they describe how the "deflection" is measured during the solar eclipse. https://eclipse2017.nasa.gov/testing-general-relativity I'm confused about the following: The last ...
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### Help me figure out how to solve the gravitational lens equations

I want to simulate gravitational lensing. In the article LENSINGGW: a PYTHON package for lensing of gravitational waves there is this fragment [page 3]: My research: As far as I understand, this is a ...
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### Is gravitational lensing "additive" in a line of sight?

As usually depicted, gravitational lensing implies, at least, three objects: a distant source, an observer, and a "massive enough" object in the middle, where enough is the mass needed to ...
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### For detection of distant galaxies by gravitational lensing-induced magnification, roughly what are the distance ratios from the lensing systems?

Discussion in comments under the question Does seeing a gravitationally lensed/magnified galaxy imply that they could also see us as well? have got me wondering about the geometry behind detection of ...
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### Does seeing a gravitationally lensed/magnified galaxy imply that they could also see us as well?

Does an observer in that galaxy see our galaxy magnified as well?
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### Cosmic shear: what is ellipticity for?

I understand that ellipticity is a very important concept in weak gravitational lensing because it describes the shape properties of the transformed galaxy. Shear, on the other hand, also describes ...
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### Would be possible to detect Planet Nine as a microlensing event along the line of its projected orbit?

Theoretically proposed by Konstantin Batygin and Mike Brown (@Caltech), Planet Nine could have a mass of $\sim 6.3 \pm 2 M_{\oplus}$. Even though I don't know if the hypothesis is still feasible at ...
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### Can we measure how fast space is expanding from how quickly gravitationally lensed galaxies or stars are blurring or getting sharper?

A galaxy that lenses another celestial body should as it moves away from Earth alter the sharpness of what it lenses by gravity. Could this be used to determine how quickly space is expanding?
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### Is gravitational lensing, optical in nature or topological?

If a large mass can adjust space geometry Like a blackhole or another star system Then is this effect optical in nature or topological? I know those sounds close, but a mirror reflects light. A mirror ...
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### If you were on a planet orbiting a star that has a black hole companion, could you see light from your host star bent 180 degrees?

I realize that there is a distance from a black hole where photons can orbit. I understand that this orbit is very unstable, but I am concerned with photons just outside this range. Could the black ...
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### Is it possible to detect gravitational lensing of both light and gravitational waves originating from the same event?

Is it theoretically possible to detect gravitational lensing of both light and gravitational waves, when both originate from the same source/event (merger of two stellar black holes or merger of two ...
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### Does the other side of the Big Bang factor into JWST observations?

Our (roughly) 13.6 billion light year view to the point of origin (big bang) is just along a radial axis. Assuming most matter ejected in a (roughly) spherical pattern, the diameter of the universe is ...
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### Can time variations in gravitational lens paths be observed & is this useful?

When strong gravitational lensing causes multiple images such as an "Einstein Cross", I understand there is difference in the time it takes the light to reach us along each path. I was ...
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### What is the galactocentric aberration?

At the Wikipedia about an aberration, there is the phrase: a recommended galactocentric aberration constant of 5.8 µas/yr What is the galactocentric aberration? How is it calculated correctly? An ...
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### Viewing black holes?

How could you possibly see a black hole when there are stars etc in front of it and then the matter being drawn into it , all you would view surely would be the objects in front of the black hole ?
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### Mega Telescope using gravitational lensing and interferometry

I have been thinking about this crazy telescope idea, but I am not smart enough to understand if it's technically possible. I understand from an engineering and practical point of view it's a long way ...
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### Is it theoretically possible to see a spiral galaxy head on, and side on, if there is a convenient gravitational lensing effect?

I was thinking this when I heard Professor Mike Merrifield say something to the effect of "unfortunately we've never seen the same galaxy side on and head on, so we can compare notes on our ...
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### Does gravitational lensing disprove the cosmic expansion theory [closed]

Recently there was a picture from the JWST that showed a galaxy that was 12.5 billion light years away. Its light had been lensed by a galaxy that was 5 billion light years away. In a static universe ...
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### Is there any method that enables us to observe the 3D large-scale spatial distribution of the dark matter?

Can we get the three-dimensional spatial distribution of dark matter through gravitational lensing? If not, is there any other way?
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### How much does foreground clumping affect the estimated sizes of high-redshift objects?

I've always converted angular to linear size by using the angular-diameter distance without really thinking about it. But in light of recent stories about high-$z$ galaxies observed by JWST being ...
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### Can two Stars form an Einstein Ring?

We know that when two galaxies are perfectly aligned they form an Einstein Ring by gravitational lensing but can two stars form it? We know gravitational bending by stars, but can two perfectly ...
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### If I can't unscramble an egg, how do Astronomers unscramble views gravitationally lensed by complex mass distributions?

Quanta Magazine's Two Weeks In, the Webb Space Telescope Is Reshaping Astronomy highlights two submissions to arXiv soon after the first images were released: "Three days later, just minutes ...
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### Gravitational mirroring: Can we theoretically see the Milky Way using a telescope?

As I am watching the beautiful deep field picture of the James Webb Space Telescope. I noticed the gravitational lensing. So I asked myself whether it is possible somehow a successive cluster of ...
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### Could "gravitational atom” black hole be detected using observation of gravitational microlensing?

D. Baumann et al., published the article hypothesizing existence of "gravitational atom” black holes (not sure whether those are just stellar ones or also those could be supermassive black holes ...
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### Black hole magnification factor

Given a black hole of mass $M$ which has a distance $D_1$ to Earth and $D_2$ to a galaxy being magnified, what is the magnification factor? And a follow-up question: Does it magnify across the ...
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### Is there a better explanation of this picture showing the very distant star "Earendel"?

"Close-up of the tiny region where Earendel happened to fall right on top of the narrow line where the magnification increases by (tens of) thousands of times. A cluster of many stars is seen ...
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### If the Sun was replaced with a sun-mass black hole, would it be visually detectable?

Assuming it had no accretion disk, could we still detect e.g. distortions of the background star field?
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### What is the maximum radius of an Einstein ring?

Is there an upper limit to how far out an Einstein ring can be visible? For black holes, is it a fixed multiple of their Schwarzschild radius?
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