Globular Clusters - The Stars that tell us the History of the Universe

Vinny Vince explores a newly observable facet of our ever-expanding universe and how it could tell the beginnings of time!

Globular clusters are groups of stars found in close proximity to one another. They are roughly spherical, made up primarily of low-mass red stars and intermediate-mass yellow stars. Within these clusters are some of the oldest stars in the Universe.

In the Milky Way, we are aware of around 150 different clusters. With traditional telescopes, they used to appear as blurry masses, but now, thanks to advances like the Hubble Telescope, they appear much clearer such that we can see their beauty.

Hubble also helped us realise that clusters don’t just have stars of similar ages – in fact, we now know that globular clusters take material from their surroundings and use it to birth new stars. Thus, older stars are found closer to the centre, whilst newer ones make up the peripherals of the complexes.

So how are these clusters formed?

When a star collapses, huge masses of gas emerge – this gas can draw together groups of stars, as they consume it. When these stars die, they eject the gas once again. However, it takes so long for a star’s life to end that we rarely ever see any new clusters form.

The clouds of gases that form clusters do not rotate “significantly” – this means that although the clusters do rotate, it is much slower than a galaxy, at around 3–6 mph. We can observe this slight motion because the clusters are slightly flattened in shape despite their spherical nature.

Recent investigations show that there is still much to learn about these star groups. A study by NASA investigated the elliptical galaxy M87, in the Virgo galaxy cluster. M87 has a massive population of globular clusters and through observing these, it was found that the formation of the clusters depends on the environment. It was also discovered that the clusters can be “snatched” by galaxies coming too close – indeed, M87 lost many of its clusters this way.

Further proof of this phenomenon came from studying the chemical composition of the clusters. M87 had three times as many clusters that were deficient in heavier elements than those that were rich in them. Nearby dwarf galaxies had many clusters deficient in the elements too, so it could be inferred that some of them were stolen by M87.

Research into globular clusters is always ongoing, and there is hope that we can use our knowledge of them to help us to understand the beginnings and growth of our universe.

References:

1) https://phys.org/news/2021-05-chemical-properties-globular-cluster-ngc.html

2) https://www.space.com/29717-globular-clusters.html

3) https://www.nasa.gov/mission_pages/hubble/science/virgo_cluster.html

4) http://www.messier.seds.org/glob.html

This article was written by Vinny Vince.