I think what’s happening is basically that the pink shows where the visible mass is, but the purple shows where the mass should be according to gravitational lensing. Dark matter should pass straight through, and that is what we see according to lensing, even though the pink lags behind because it can collide (since it’s mostly the hot plasma).
At least, I think that’s what’s happening… I myself am really confused and am pretty unconfident in that explanation.
I’m also confused as to what modified gravity predicts, and how bullet clusters disprove it. I guess what we’d see is that modified gravity would alter the gravity around the visible mass, not just make it magically act like it just passed through. Ie, a lot about gravity would have to change for such a drastic difference between the mass as perceived through x-rays and the mass as perceived through gravitational lensing.
I think what’s happening is basically that the pink shows where the visible mass is, but the purple shows where the mass should be according to gravitational lensing. Dark matter should pass straight through, and that is what we see according to lensing, even though the pink lags behind because it can collide (since it’s mostly the hot plasma).
At least, I think that’s what’s happening… I myself am really confused and am pretty unconfident in that explanation.
I’m also confused as to what modified gravity predicts, and how bullet clusters disprove it. I guess what we’d see is that modified gravity would alter the gravity around the visible mass, not just make it magically act like it just passed through. Ie, a lot about gravity would have to change for such a drastic difference between the mass as perceived through x-rays and the mass as perceived through gravitational lensing.
Here’s a link that seems to confirm what I wrote: https://chandra.harvard.edu/graphics/resources/handouts/lithos/bullet_lithos.pdf