A dramatic Einstein ring seen by Webb | Hacker News Reader

A dramatic Einstein ring seen by Webb

phys.org

122 pointsprogramd28 comments

https://esawebb.org/images/potm2503a/ ("Spying a spiral through a cosmic lens")

https://www.esa.int/ESA_Multimedia/Images/2025/03/Webb_spies... ("Webb spies a spiral through a cosmic lens")

Some clarifying context not present in this OP (phys.org): this is a composite of Hubble visible-light images with Webb data.

Has someone come up with a way to de-warp an object seen as an Einstein ring? I thought I had read someone doing this, but maybe it was they were trying to do this. Maybe it was during the discussion on using Sol as a gravitational lens like this?? Seems like some interesting math to put the image in TFA back into the shape of a galaxy.

Dewarping it mathematically should be fairly easy if the lens' gravitational field is sufficiently uniform. Problem is more the amount of detail we actually have in these pictures to expand the most compressed parts.

I wonder if correctly dewarping would help get a measurement of distance of the lensing object. Would that then be able to help recalibrate/confirm our understood distances/scale/etc?

Can someone with the knowledge explain, is the close elliptical galaxy actually just the small dot of light in the centre and the spiral galaxy is behind it but dramatically magnified by the lens effect?

Yes the elliptical galaxy is the fuzzy blob in the middle; blended with the galaxy behind, it's difficult to see the diffuse outer parts of it. I'm not sure how much the apparent size of the spiral is affected by magnification, vs how much is just relative size difference. I guess it would be useful to know the distance between them.

Wow I get the distances aren’t shown, but still, the magnification is impressive.

Yep, although the elliptical galaxy also includes the diffuse glow around the small dot of light.

The galaxy behind it is magnified, and also distorted.

> Of course, this image is only possible because of our vantage point. Astronomers in other galaxies wouldn't catch such a wondrous image.

Well no, but they probably would catch other wondrous images we can't catch due to our vantage point.

Are diffraction spikes of light not present because everything in the picture is a galaxy and not stars? Or do they remove them now with processing?

Here’s what I mean: https://webbtelescope.org/contents/media/images/01G529MX46J7...

"While all stars can create these patterns, we only see spikes with the brightest stars when a telescope takes an image."

These distant galaxies are incredibly faint, so I imagine that's the reason there are no obvious diffraction effects.

Yeah, the diffraction spikes in Webb/Hubble images are clues that those stars are nearby within the Milky Way.

Because the aperture isn't made up of nice straight edges.

Can somebody knowledgeable please tell me what's the distance from Earth to these galaxies?

> beauty is not only in the eye of the beholder, but also where that beholder is.

I love this

this should be able to be used to test dark matter theories.

They're not collecting all of this data to make pretty pictures, it's going to be used to test all sorts of theories. Ones that explain Dark Matter as well.

(I do agree with Angela Collier, youtuber nee physicst, Dark Matter is not a theory, it's an observation. We've looked out into the universe and have seen something that we call Dark Matter that our current theories don't match up with.)

it's a theory. when you present multiple observations just the fact that you group them together is not a value-free action and implies a common cause. calling it an observation is a crude and philosophically improper attempt to elevate it to a less refutable status.

This feels like you'd say that just because apples fall from trees and a bowling ball falls in much the same way when tossed off a building, that grouping those things together implies a common cause and that we should call that cause a theory because we aren't 100% certain that they are caused by the same effect.

They could be two different reasons.

I do prefer Occom's razor for these things. We've seen a bunch extremely large celestial objects move in ways that our models cannot account for with the things that we can see. Sure, there could be more than one thing out there causing all of those extremely similar effects. But that's far less likely than there just being one reason.

It's pretty reasonable to invoke occam's razor for claiming that in general unexpected galaxy rotation curves have a common explanation. It's another thing to claim without blinking an eye that these are phenomenologically connected to baryon acuoustic oscillations in the CMB (which is what Angela does)

Since it's been a _long_ time since my physics undergrad I honestly can not speak to how baryon acoustic oscillations tie into dark matter. Hell the paper describing it came out after my first trip through college!

I'll confess the paper is a bit over my head. Astrophysics was never my passion and I became a software engineer right out of college anyways, so I'm a little rusty. However, in the 2005 paper they state that the BAO, specifically the way that the BAO has propagated, can't be explained by baryonic matter alone, which in their words would show a much larger effect than observed. This seems to be yet another observation that is consistent with dark matter.

However, since you must be a working astrophysicist, could you enlighten me with what you think is wrong with the interpretation of those observations? Do you think the >3 sigma confidence isn't enough for astrophysics?

I am genuinely curious.

This is, in fact, part of the support for Dark Matter, both with galaxies (the amount of lensing requires the galaxy to include a lot of Dark Matter) and between galaxies, where other lensing effects occur that can only be explained by filaments of Dark Matter between galaxies and galaxy clusters.

This is a great podcast, with episode 6 concentrating specifically on Dark Matter and the evidence for it: https://podcasts.apple.com/us/podcast/crash-course-pods-the-...

no. you can't say it's evidence for dark matter versus any given other theory until after you have computed the expected metrics created by any alternative theory.

in any case, you can't say it's support for dark matter in this specific case without actually running the numbers (what are the rotational speeds and what is the bending curvature)

dark matter halos must have a somewhat specific distribution that goes beyond the perimeter of the visible galaxy itself.

however the more that i think about it this example is likely to be unhelpful. the closer galaxy looks elliptical and most dense elliptical galaxies "have no dark matter" (in basic MOND this is a phenomenon that falls out if the gravity law). We'd really need lensing from a more "normal" looking galaxy.

I wasn't saying, as a layman, that this is evidence for Dark Matter. I'm saying that the current thinking in astrophysics is that this is evidence for Dark Matter. Katie Mack, the astrophysicist in the podcast I linked, is a reknowned expert, and discusses how running the numbers on exactly these things provides evidence for Dark Matter, and how alternatives fail.

then she is being misleading, at best. To date no observed galaxies (versus galaxy clusters) have had the arrangement (as is in this image) wherein the galaxy is so perfectly in line with a background galaxy and close enough to estimate the rotation curves (and the background galaxy is of the right disposition to know if dark matter halos extend beyond the galaxy and estimate by how much space). Without both those factors it's really difficult to do a proper correlation of dark matter distribution around galaxies and the observed light bending.

She does not specifially address this scenario. I offered the link as a general dive into the evidence behind Dark Matter as it relates to lensing.

I regret that now.

>I regret that now.

I, on the other hand, am thankful for it. I love watching Anton Petrov, PBS Space Time, and various other experts and communicators in anything space-related. This looks like a great podcast that slipped me by, so I appreciate the link.

ok I apologize. She is not being misleading intentionally, but it's pretty clear, then, that it's easy to be misled into overly broad generalizations about the confidence we should have about cosmology by the things that she says.

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