A proof of concept for hidden mass

33:06uh that's producing a a strong gravitational lensing effect. >> Mhm. >> So, here uh there's G1 through G4. You see them labeled there. And then there's this giant blue arc. >> Yes. >> So, that blue arc is a galaxy that's behind this this cluster. >> Mhm. >> So, that background galaxy is being lensed around, you know, and it forms this distorted arc. And you see there in the bottom right that galaxy G4, which is associated with this other group of galaxies >> Yes. >> It happens to be right on top of the arc. >> Yes. >> And you can see that the arc does this

33:47little, you know, jog around G4, right? So, the G4 is here splits this arc in two. Uh and you can imagine that even if you didn't see uh G4 at all, here we can see it because it has enough stars to be detected directly. But, even if we couldn't see G4 there, we could infer that there's some massive object at that position because the arc is split around it. >> would be split split around it. And And this And the the arc is massive. I mean, it's so And so, would would this be an example of strong gravitational lensing? >> Yeah, that's right. So, the here G1 through G3 and uh yeah, G1, G2, and G3,

34:29they are massive enough to produce two images uh of this background galaxy. You see that there's another little counter arc there on the left. >> On the left, yep. >> Uh so, here those guys are producing the the lensing effect and then we're we can detect this the presence of this other clump because it's impinging on the lensed image of this background source. >> Yes. Makes sense. Makes sense. This is so fascinating. It's like kind of a hard thing to visualize or to mentally uh track. I think the fish tank analogy was very helpful in trying to create some grounding. Um you know, because I think what you're

35:10part of what your point is in if we look at this image and I think where we're going with this is let's imagine G4, which is right on the arc, which is the lens from the background galaxy that G1 through G3 are creating. If G4 was not had no light, there was no point light source, because it's so massive, it's having its own almost mini lens on the other lens, we could subsequently make some characterizations about G4 being there because it is impacting the larger lens from G1 through G3. Is that Is that correct? >> Yeah, exactly. So, here, you know, it Here G4 is so big that it has a galaxy

35:52in it and we can see the galaxy, right? So, this is just a proof of concept. What we're really interested in is these dark matter clumps that don't have galaxies. Conceptually, it's it's very similar, right? They would introduce some perturbation or some small deformation of the lensed image, right? It wouldn't be as obvious as as this case, but the idea is is the same. >> I I I get it now. I get it the the the canvas on which you're trying to paint is the lens itself. You can look at the light arcs, you know, that are happening and see do we see anything any perturbations in the light arcs or the lens where there are not necessarily point light sources like

36:33a large galaxy? Because if you do see that, that is a potentially good candidate or indicator of underlying dark matter clumps uh on the lens. >> Yeah, exactly. Very interesting. >> you know, >> Very interesting. >> And what helps what helps look at smaller clumps is actually having a more compact source. >> Okay. How do you How do you mean?