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"Then there are cases of galaxies which don't contain any dark matter..." You mean zero at ALL, or with little measurable effects?
by thegabriele 6y ago
"Then there are cases of galaxies which don't contain any dark matter..."
You mean zero at ALL, or with little measurable effects?
- occamrazor 6y agoWe don’t know, more likely the latter. We can see that some galaxies rotate as if they had no dark matter, but we don’t know why their dark matter isn’t there.The prevalent, but still speculative, hypothesis is that it was “stolen” by a bigger galaxy in a close pass-by.
- enkid 6y agoSo does dark matter interact with itself outside of gravity? If not, how does the visible matter separate from dark matter.
- antepodius 6y agoIf you imagine that dark matter and visible matter both start out basically smoothly distributed in a big cloud, they'll both tend to collapse inwards. The matter forms a rotating disk because the particles of matter interact through non-gravitational means; so ones that get close can exchange (and cancel!) momentum. But if dark matter only interacts gravitationally, it won't do this; the particles will just fall through the center of the future galaxy, 'passing through' each other (and the matter). Gravitational drag presumably adds some rotation to the dark matter over time; I don't know. But that's how dark matter and regular matter could separate. >So does dark matter interact with itself outside of gravity? There are different ideas about what dark matter could be. Some have it interacting through other forces (WIMPs interacted through the weak force, for example), some are purely gravitational. There's always talk of 'dark matter candidates', theoretical or otherwise particles that could plausibly be dark matter.