Globular clusters younger than thought?

Globular clusters are thought to be some of the oldest objects in the Universe at about 13 billion years old. But a new study suggests they might be nine billion years old, potentially changing what we know about the evolution of our Galaxy.

An illustration of a binary star system within a globular cluster. Credit: Mark A. Garlick/University of Warwick

Globular clusters may be four billion years younger than previously thought, according to a new study.


Globular clusters are tight pockets containing hundreds of thousands of densely-packed stars, and are thought to be just slightly younger than the Universe itself, which is estimated to be 13.8 billion years old.

The current understanding is that globular clusters formed around the same time as galaxies, which explains why we find them peppered around the centre of the Milky Way.

But this new study by scientists at the University of Warwick suggests that globular clusters could be as young as nine billion years old.

Between 150 – 180 clusters are thought to exist in the Milky Way alone, so re-calculating their estimated age could bring into question astronomers’ knowledge of how the Galaxy and the Universe formed.

The team used computer simulation software called Binary Population and Spectral Synthesis (BPASS) to look at the evolution of a binary star system (two stars orbiting one another) within a globular cluster.

This showed the two stars interacting, where one star expands while the smaller star strips away the larger star’s atmosphere.

Calculating the age of the binary star systems, the scientists were able to show that the stars were formed at the same time as the globular cluster.

Determining ages for stars has always depended on comparing observations to the models which encapsulate our understanding of how stars form and evolve,” says Dr Elizabeth Stanway of the University of Warwick.

Globular cluster Omega Centauri is thought to contain about ten million stars. These ancient objects may not be as old as once thought.Credit: ESO
Globular cluster Omega Centauri is thought to contain about ten million stars. These ancient objects may not be as old as once thought. Credit: ESO

“That understanding has changed over time, and we have been increasingly aware of the effects of stellar multiplicity – the interactions between stars and their binary and tertiary companions.

“If true, [this study] changes our picture of the early stages of galaxy evolution and where the stars that have ended up in today’s massive galaxies, such as the Milky Way, may have formed.


“We aim to follow up this research in future, exploring both improvements in modelling and the observable predictions which arise from them.”