According to globular clusters, the universe is 13.35 billion years old.

It is a widely accepted theory today that when the first stars formed in our universe approximately 13 billion years ago, they quickly came together to form globular clusters. These clusters joined together to form the first galaxies, which have been growing through mergers and evolving ever since. For this reason, astronomers have long suspected that the oldest stars in the universe are found in globular clusters.

Therefore, studying the stars in these clusters is a means of determining the age of the universe, which is still subject to some conjecture. In this sense, an international team of astronomers and cosmologists recently carried out a study of globular clusters to infer the age of the universe. Their results indicate that the universe is about 13.35 billion years old, a result that could help astronomers learn more about the expansion of the cosmos.

Their study, titled “Inferring the Age of the Universe with Globular Clusters,” recently appeared online and was submitted for consideration to the Journal of Cosmology and Astroparticle Physics. The study was led by David Valcin, predoctoral researcher at the Institute of Cosmos Sciences of the University of Barcelona (ICCUB), who was joined by a team from France, Spain and the United States.

As noted, globular clusters are of particular interest to astronomers given their unusual nature. These spherical collections of stars are located in the halo of a galaxy that orbits beyond the galactic nucleus and are considerably denser than open clusters (found in the galaxy’s disk). Most globular clusters are also of uniform age, and contain older stars that have entered their giant red branch (RGB) phase.

In fact, studies of globular clusters in the Milky Way Galaxy have shown that some of the oldest stars in our galaxy exist within them. While the origins of globular clusters and their role in galactic evolution remain a mystery, astronomers believe that studying these collections of ancient stars will yield valuable information about both. As Valcin and colleagues shared with Universe Today via email:

“Globular clusters are among the earliest star structures formed in the universe and therefore can be used as a good estimator of the time of galaxy and star formation to infer the age of the universe. From one point of view astrophysicist, they provide a wealth of information on the formation and evolution of galaxies and stars. “

For the sake of their study, the team examined 68 galactic globular clusters, which were observed by the Advanced Survey Camera (ACS) of the Hubble Space Telescope. Specifically, they studied the distribution of stars in these clusters based on their magnitude, which was obtained by using a modified version of isochrones to model the data.

This software package takes synthetic photometry provided by stellar models and then interpolates their magnitude based on where stars of the same mass are found on the evolutionary trajectory at the same age. Valdin explained:

“Using the catalog from the Sarajedini et al (2007) survey of globular clusters with the Hubble Space Telescope, we extracted information from the Color Magnitude Diagram of Globular Clusters using theoretical isochrones (the isochrones are a set of stellar models calculated at the same age for a range of different masses.) In fact, the way stars are distributed on the diagram according to their magnitude and color may restrict the sensitivity of the parameters of stellar isochrones, which correspond to a population of stars with the same age. “

Similarly, the team relied on the Mesa Isochrones and Stellar Tracks (MIST) stellar model, as well as the Dartmouth Stellar Evolution Database (DSED). In the end, they obtained an estimate of the average age of the oldest global groups of 13.13 billion years. After taking into account the amount of time it would take for these globular clusters to form, they were able to infer an age estimate of 13.35 billion years.

This result has a confidence level of 68% and includes an uncertainty range of ± 0.16 trillion years (statistical) and ± 0.5 trillion years (systemic). This value is consistent with the previous age estimate of 13.8 ± 0.02 billion years, which was inferred by data obtained by Planck’s mission in the cosmic microwave background (CMB): the remaining background radiation created by the Big Bang that is visible in all directions.

Furthermore, the above estimate depends on the CDM cosmological model, a version of the Big Bang model that contains three main components: dark energy, “cold” dark matter (CDM), and ordinary matter. This essentially means that globular clusters can precisely constrain the age of the universe in a way that does not depend on theoretical models.

Furthermore, since their age estimates are consistent with estimates based on cosmic expansion, this information could also provide clues to the latter. Of course, Valdin and his colleagues acknowledge that more observations and data are needed if scientists hope to discover why there has historically been a discrepancy between age estimates in the first place:

“In the current uncertainty about the expansion of the universe, it is important to collect more data on which interpretation is as independent from cosmology as possible to understand the origin of the discrepancy. Although globular clusters do not provide a direct measure of expansion, we allow limiting the age of the universe, which may be related to expansion. The age of the universe is also determined by CMB observations, but this determination is highly model dependent. A valuable aspect of estimating expansion is the fact that it is obtained without assuming any cosmological model. The agreement between these two measurements can be used to confirm important aspects of the cosmological model. ”