Star clusters age differently

Much like their human equivalents, scientists have found that not all star clusters age at the same rate.


Scientists at the University of Bologna, Italy, studied 21 clusters of stars from images collected by NASA’s Hubble Space Telescope and the European Southern Observatory. Based on a new type of analysis they found that some clusters are younger-looking than their age would suggest while others are looking a bit old for their years.

They used a particular type of star known as ‘Blue stragglers’ which are so heavy they tend to drift towards the core of the cluster as time passes. This allowed the astronomers to use Blue stragglers as a type of ‘cosmic clock’, based on their distribution, to gauge the average age of the stars in that cluster.

“By studying the distribution of a type of blue star that exists in the clusters, we found that some clusters had indeed evolved much faster over their lifetimes, and we developed a way to measure the rate of aging,” says Francesco Ferraro, of the University of Bologna in Italy.

The astronomers knew that all the clusters were roughly the same age but they found that some clusters had much less drift from Blue stragglers than there should have been, while others had ‘prematurely aged’ with all their blue stars clumped at their centre – the cosmic equivalent of middle-age spread. 

“Since these clusters all formed at roughly the same time, this reveals big differences in the speed of evolution from cluster to cluster,” co-author Barbara Lanzoni, also of the University of Bologna, told

“In the case of fast-aging clusters, we think that the sedimentation process can be complete within a few hundred million years, while for the slowest it would take several times the current age of the universe.”

While it is early days for this type of analysis, the scientists hope that their findings could be used to develop a ‘dynamic clock’ that measures the ages of different stellar systems. The findings are published in a paper in the journal Nature.