Rotation Curves

Measured curves are rather flat:
Velocity remains constant as distance from center increases.
This is an unexpected result!

For a central mass velocity falls with distance like in the solar system.
Orbit of Pluto is 39 times longer than Earth's
But Pluto year is 247 Earth years because moves slower.

Although light in the plane is blocked we can also measure the rotation curve of our own galaxy using radio waves...