How do Astronomers Work Out the Age of Stars?

This is a common question I often receive during my stargazing talks.

So, how can we accurately determine the age of stars that are millions or even billions of years old? It’s a fascinating process that involves a combination of scientific methods and advanced technology. Let’s dive into the world of astronomy and explore the various techniques used by astronomers to uncover the age of stars.

This is the spectrum of our Sun

Stars, like living beings, go through a life cycle known as stellar evolution. Just like humans grow from infants to adults, stars also undergo different stages of development. By studying these stages, we can estimate the age of a star.

One of the primary methods used to determine a star’s age is through spectral analysis. This involves studying the light emitted by a star and analyzing its spectrum. By examining the elements present in the star’s spectrum, scientists can determine its chemical composition and infer its age. Knowing what stars are made of not only helps determine their age but also provides insights into how they formed, whether they are moving towards or away from us, and what type of star they are.

Another important tool in determining stellar age is the Hertzsprung-Russell (H-R) diagram. This diagram plots a star’s brightness (luminosity) against its temperature. By comparing a star’s position on the H-R diagram with theoretical models, we can estimate its age. Stars follow specific evolutionary tracks on the diagram, allowing us to determine their stage of development.

In the case of stars, you are truly judged by the company you keep. Studying star clusters, which are groups of stars born from the same molecular cloud, provides valuable insights into stellar ages.

Astronomers study the properties of star clusters, such as their colour and brightness, to estimate the age of the stars within them. Younger clusters contain hot, massive stars, while older clusters have cooler, less massive stars.

NGC4755 (Jewel Box) a group of young stars
Omega Centauri – a cluster of very old stars

These molecular clouds or star-forming regions are the result of supernovae.

Eta Carina a star forming region in southern Milky Way left over from a supernova

A supernova is the explosive death of massive stars. For example, stars like Betelgeuse, Sirius, and Antares are candidates for going supernova. After these stars explode, they leave behind remnants that can help determine the age of surrounding stars. By analysing the expansion rate of supernova remnants and comparing it to known supernova events, we can estimate the age of nearby stars.

Examples of Supernovae in other galaxies Credit: ESA

In summary, astronomers use a range of techniques to determine the age of stars, including spectral analysis, the Hertzsprung-Russell diagram, cluster analysis, and studying supernova remnants. By combining these methods with advanced technology and theoretical models, we can unlock the secrets of the universe and gain a deeper understanding of stellar evolution.

So, the next time you gaze up at the night sky, remember that behind the twinkling stars lies a wealth of knowledge waiting to be discovered. The age of stars is just one piece of the cosmic puzzle that astronomers are working to solve. That is one of coolest things about being an astronomer – there is so much to learn, so much we don’t know and the possibility of discovering new objects as well as adding to our overall knowledge