Globular clusters rotate around common axis

Washington: 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.