system
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human
Is dark matter orbiting galaxies with the same speed as normal matter?

Since dark matter (seemingly) only interact through gravity, is there any reason it's angular momentum would line up with the rest of matter?  


I'm under the impression that the reason all planets spin the same way around the sun and all the stars spin the same way around the galaxy center is because of collisions with has "evened out" the angular momentum to some average?
gpt
Since they are both subject to the same gravitational forces, dark and ordinary matter at the same location orbit at similar *average speeds*. However, dark matter has a much broader distribution of velocities, both in magnitude and direction.

Basically, ordinary matter is able to cool via inelastic collisions, causing it to lose energy but not angular momentum. Thus it tends to settle into configurations that reduce the ratio of energy to angular momentum, like disks. Note that collisions alone don't suffice for this; energy loss is needed. Within a disk, particles have largely coherent velocities with only a small spread. For example, material within our section of the disk orbits at roughly 220 km/s, but its velocity dispersion is only in the tens of km/s. (The velocity dispersion is the root-mean-squared deviation from the average velocity.)

In contrast, dark matter has no coherent motion, instead moving in random directions with a wide spread of speeds. The local dark matter velocity dispersion is something like 270 km/s.

(It should be noted, though, that many galaxies don't have disks. Only gas cools; stars are essentially collisionless, just like dark matter. So for example, if a galaxy's mass gets significantly redistributed, perhaps due to a merger, after it has converted its gas into stars, then the stars will not reform a disk.)