Dark Matter

So V_rot ~ constant over the disk of the Galaxy. This should confuse the hell out of you. Why?

What does the rotation curve of the Solar System look like? V_rot ~ 1/sqrt(r). Why?

What should the rotation curve of the Milky Way look like?

What does it mean that the rotation curve is flat? Look at the dynamical mass:

So as we go further and further out in the galaxy, there is more and more mass. But what does the distribution of stars do?

Our Galaxy isn't the only one that does this:

Dark Matter

There's a lot of stuff out there.

Dynamical mass estimates: 5-10 x 10¹¹ M_sun
Star + Gass mass: < 10¹¹ M_sun

So 80-90% of the Milky Way's mass is invisible. Whoa....

What could dark matter be?