What behavior do galactic rotation curves exhibit to suggest the existence of dark matter in an extended halo?

The gravitational effects. For example, gravitational lensing; also, galaxies spin way too fast for the amount of known matter.

This is the correct answer I got it right in a test for school I took. Here it is The motions indicate a greater gravitational pull from what we see of it

The motions indicate a greater gravitation pull than from what we see.

Dark energy is the force that expands the universe. Dark matter is the force that keeps everything from crashing into one an other. Dark matter is what keeps galaxies together for example if you pour...

dark matter is what keeps galaxies together for example if you pour beads (representing stars planets etc) in a tub they spread out but if you get a fan (representing dark matter) it is possible to...