Globular clusters rotate around common axis

While studying some of the oldest star clusters in our galaxy, astronomers from the University of Texas at Austin and Germany's Max Planck Institute for Extraterrestrial Physics (MPE) found that the stars at the centers of these clusters are rotating around a common axis.

It was previously thought any central rotation would have been long erased, leaving the central stars to random orbits.

These "globular clusters" are ancient collections of up to a million old stars with simple chemical compositions, tightly bound together by gravity.

Globular clusters orbit most galaxies, including our own Milky Way. Due to these clusters' old age and fairly spherical shape, with a strong concentration of stars towards the center, they have historically been viewed as simple systems. However, new observations keep revealing surprising results.

The team, led by MPE's Maximilian Fabricius and including Texas' Eva Noyola, observed 11 globular clusters from the University of Texas at Austin's McDonald Observatory with the Harlan J. Smith Telescope. They found that all of the clusters show this central rotation.

This result is "astonishing," Fabricius said. "We did not expect this; originally we observed these globular clusters to measure their central velocity dispersions"-that is, the random motions of stars within a cluster.

The findings are set to be published in the Astrophysical Journal Letters.