Image caption Most stars are formed in stellar clusters like this one

Using the Hubble Space Telescope, astronomers have managed to measure the motion of stars in a stellar cluster.

Most stars are formed in these clusters, and this particular one, in the nebula NGC 3603, is one of the largest and most dense in the Milky Way.

The scientists discovered that stars in the cluster were not moving in the way they anticipated.

The discovery sheds new light how these stellar nurseries evolve and disperse.

Boyke Rochau from the Max Planck Institute for Astronomy in Heidelberg, Germany, who led the research, explained that the cluster contained thousands of stars with masses between a tenth of the mass and 120 times the mass of our Sun.

He said that he and his colleagues sought to track their movement, "to look at the dynamic evolution of these important objects and see how long clusters survive".

Mr Rochau explained the "extraordinary precision" of Hubble allowed them to do this.

Image caption The cluster is one of the most massive and dense in the Milky Way

"We were also able to study two images of the cluster that were captured [by Hubble] a decade apart," he explained.

Using these images, taken in 1997 and 2007, the scientists measured the precise speeds of more than 800 stars. These measurements revealed that the cluster had not yet "settled down" as the team had expected.

"When the cluster reaches equilibrium, we would expect that the lower mass stars move [faster] than the higher mass stars, but this wasn't the case," Mr Rochau explained to BBC News.

This, he suggested, is because the conditions in the cluster still reflect those from the time it was formed, approximately one million years ago.

The researchers hope that by monitoring such objects for an even longer period of time, they will be able to provide new clues about how clusters eventually "dissolve" into galaxies.