Answer to Question #173618 in Astronomy | Astrophysics for ANJU JAYACHANDRAN

Question

3e) Discuss the rotation curve of our Galaxy. What inferences can be drawn from it

about the structure of our Galaxy?

Answer 1

The rotation curve of the Galaxy is the dependence of the circular velocity on the galactocentric distance in the plane of the Galactic disk.

This picture taken from en.wikipedia.org shows the observed rotation curve in blue. We can see that the graph is not a straight line, so the Galaxy does not rotate like a solid body. It also rotates not like a keplerian disk, so not all the mass is situated at the center of the Galaxy. But the prominent increase of the curve at small distances is due to the bulge and the small radial scale of the disk.

We can also see that the curve does not decrease even at distances of 12-15 kpc from the Galactic center, so there may be a great mass at the outskirts of the Galaxy. We may note that a large fraction of galaxies has flat or even increasing rotation curves, so there may exist a great amount of the dark matter.