Submitted by karmagheden t3_11yjstz in space
boundegar t1_jd81ldo wrote
But... dark matter also doesn't interact with normal matter, so how would it create friction?
luckybipedal t1_jd8vyjo wrote
They talk about dynamical friction, which is a result of gravitational interactions. It's new to me too. I found this high level explanation: https://astronomy.swin.edu.au/cosmos/D/Dynamical+Friction
magnamed t1_jd9s85y wrote
Just wanted to shoot you a thanks for the link.
the_funambule t1_jda2h67 wrote
you had me in the first half ngl
magnamed t1_jda6fxh wrote
Yeah I guess that doesn't really come across all that well over text. Didn't mean anything bad by it.
the_funambule t1_jdal86e wrote
Oh I am just messing around! I know what you meant :)
Optimal_Ganache8605 t1_jdahzaz wrote
This sounds like tidal heating in a way.
cratermoon t1_jd9hzvx wrote
As noted in the other comment, this isn't the common mechanical friction. It's the same "friction" of the moon's gravity causing the earth's rotation to slow down at a barely perceptible rate.
s1ngular1ty2 t1_jd9r2h7 wrote
It's not normal friction. It's dynamical friction. Friction from gravity. Dark matter is matter and therefore creates gravity. It interacts with any other matter via gravity.
75MillionYearsAgo t1_jd8huam wrote
No idea. Universe is wierd as hell though so i’m sure its possible. I mean we don’t even know why gravity happens, we just know how it works. Maybe smth similar with the friction thing.
Mighty-Lobster t1_jdat4zw wrote
>But... dark matter also doesn't interact with normal matter, so how would it create friction?
Dark matter interacts via gravity. Dynamical friction is a byproduct of gravity. When you have a large massive body inside a sea of much smaller particles, the large body's gravity changes the orbits of the particles near it in a way that creates an overdensity of small particles behind the large object. That overdensity creates a gravitational pull from those particles, in the direction opposite to the body's motion. Therefore, it behaves similar to a friction force.
Dynamical friction happens in any N-body system with a sea of "small" particles and some large particles. For example, it is the reason why supermassive black holes have to always be at the center of their galaxy. Dynamical friction with the stars would bring them in.
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