The Motion of other Stars
- The motion of stars in the range of 1 kpc to
16 kpc from the galactic centre has been measured.
- The stars move approximately on circular orbits about the
galactic centre along with small peculiar velocities.
- For most of the stars, the velocities range between
200 km/s to 250 km/s.
- The plot of velocity versus distance from the centre
of the galaxy is called a rotation curve.
- The most important feature of the rotation curve
is that the velocity of stars far away from the galactic centre
stays at a large value near 220 km/s.
- This is not what was expected, because there is almost no
stars at 16kpc, where we still see 220 km/s rotational velocity.
According to Kepler's Laws, the velocity on circular orbit that encompasses
all gravitation mass is
i.e should drop as square root of radius,
- while angular velocity should drop as