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NOND and alternatives are less and less likely with more evidence. The fact that there seems to be galaxies without dark matter formed after high velocity coll
by nabla9 4y ago
NOND and alternatives are less and less likely with more evidence.
The fact that there seems to be galaxies without dark matter formed after high velocity collisions is clear indicator that dark matter is weakly interacting matter.
When two galaxies collide in high velocity, gases in these galaxies collide and slow down while most stars and dark matter continue with higher speed. Gases from new galaxies without dark matter, remaining galaxies have stars and dark matter but no gases.
A trail of dark-matter-free galaxies from a bullet-dwarf collision
https://www.nature.com/articles/s41586-022-04665-6 https://www.nature.com/articles/s41586-022-04665-6
- Ygg2 4y agoSure that's the issue. The old models are wrong and the new models can't compete.
- nabla9 4y agoSo far there is nothing saying old models are wrong. Only the mainstream dark matter hypotheses that matches all the evidence is some type of particle that is not interacting. The difficulty is in detecting. Weakly interacting massive particles are by definition hard to detect directly. MaCHOs, modified gravity etc. match some, never all the evidence.
- ccvannorman 4y agoIt matches all the evidence because we looked at the available evidence and highly tweaked the model until it matched. There has been no direct observation of Dark Matter, so saying "it matches all the evidence" may be redundant, since by definition, we said "Let's create something that matches all the evidence and look for it."
- nabla9 4y ago>It matches all the evidence because we looked at the available evidence and highly tweaked the model until it matched. This is just wrong. This is not question of parameter tuning. There is class of theories that include weakly interacting particles, you may tune or select model among these. But the most evidence (even newly discovered) points toward dark matter being particles because they behave like particles.
- Ygg2 4y agoI don't follow. The theories made prediction that came empty handed again and again. Sure, absence of evidence isn't evidence of absence, but you can search for star spangled swan only so much, before looking into alternatives.
- towaway15463 4y agoWhat if the effect is dependent on the concentration of high mass objects like the stars themselves? Instead of the stars being embedded in dark matter they are in a field that modifies gravity.
- throwawaymaths 4y agoThey are all faint galaxies, so any estimates on their baryonic mass are in the "challenge your assumptions" regime. And that "line" is pretty spurious, if I'm reading the paper correctly they are saying the chance of the line happening randomly is 0.6% -- not very low, the sky is a huge place. the bullet galaxy that has the "rest of the dark matter" hasn't been found.