Rotation Curves

The rotation curve of a galaxy is the variation in the orbital circular velocity of stars or gas clouds at different distances from the center. The manner in which the velocities vary with radius reflects the distribution of mass in the galaxy:

Most galaxies have rotation curves that show solid body rotation in the very center, following by a slowly rising or constant velocity rotation in the outer parts. Very few galaxies show any evidence for Keplerian decline. A flat rotation curve implies that the mass continues to increase linearly with radius. Therefore, the rotation curves of galaxies present strong evidence for dark matter.

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