Comment by throwawaymaths
Comment by throwawaymaths 2 days ago
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.