What do globular clusters’ radial velocities show about their orbits around the Milky Way?

Radial velocities of globular clusters, measured via the Doppler effect from their integrated spectra, provide critical insight into their motion through the Milky Way Galaxy. These measurements indicate that globular clusters travel around the galactic centre in highly elliptical orbits.12

While the globular cluster system as a whole exhibits a rotational velocity of approximately 180 km/sec relative to the Sun, or 30 km/sec on an absolute basis, individual clusters show significant variation in their speeds. For example, observed radial velocities range from large negative values, such as 411 km/sec for NGC 6934, to large positive values, such as 494 km/sec for NGC 3201. These high velocities and the resulting orbital paths are fundamental to understanding the dynamics of these ancient star clusters within the galactic halo.123