Stellar discovery could prompt a rethink on the universe

A binary star evolution within a globular cluster. These star-packed balls could be billions of years younger than we think. Image / Mark A Garlick, University of Warwick

Powerful new models co-developed by a University of Auckland astrophysicist have led to a discovery that could change what we understand about the universe.

Findings detailed in a just-published study brings into question current theories on how galaxies, including our own Milky Way, were formed.

The discoveries centre on what are called globular clusters - effectively tight balls densely packed with up to a million stars each.

Between 150 to 180 of these are thought to exist in our galaxy alone, and they've long thought to be almost as old as the universe itself.

But thanks to newly developed research models it has been shown that they could be as young as nine billion years old, rather than 13 billion.

Within a globular cluster, Binary Population and Spectral Synthesis (BPASS) models are able to explore the colours of light from old binary star populations, as well as the traces of chemical elements seen in their spectra.

Previous versions have focused on massive stars because they were brighter, bigger and are easier to see in more distant galaxies.

They also had short lifetimes of a few million years and die in luminous supernovae, so scientists deemed them more important to look at first.

An updated BPASS model, which the University of Auckland's Dr JJ Eldridge helped develop, instead concentrated on "intermediate" mass stars similar in size to the Sun.

These have lifetimes of billions of years, so dominated the light that could be seen in very old galaxies and old star clusters.

The new model ultimately allowed the scientists to study stars that were 100 times older than they could previously.

"We've compared our model star clusters to those that we observe and found that the ages from this comparison are at least a few billion years younger than previous estimates," Eldridge said.

"Our re-evaluation of ages indicates that any study where we use the stars we detect in a galaxy or star cluster to estimate its age may have overestimated the ages of those galaxies.

"While this is a tentative result, we really need to check this as it would have important implications for how galaxies evolve and form - even our understanding of how our own Galaxy evolved may change."

The next steps would be to look at nearby globular clusters in which all stars could be observed, allowing scientists to understand the ages of the clusters in much greater detail.

"We really need to understand exactly why we've had this big change in the estimated age."

Study lead author Dr Elizabeth Stanway, of the University of Warwick's Astronomy and Astrophysics Group, said the findings pointed to many new avenues of inquiry.

"It's important to note that there is still a lot of work to do - in particular looking at those very nearby systems where we can resolve individual stars rather than just considering the integrated light of a cluster - but this is an interesting and intriguing result," Stanway said.

"If true, it 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."