The Theory of Nothing

What the heck are star clusters?

What the heck are star clusters?

Star clusters are not gatherings of celebrities. They're astronomical objects. Basically, a star cluster is what its name suggests, a group of stars, but it's not just any old group of stars. It's stars that are gravitationally bound to one another.

There are two main types of star clusters: globular and open. Globular clusters are spherical in shape and consist of up to a million stars. A globular cluster can be up to 30 light years in diameter, which is not all that much space to stuff that many stars into.

Our galaxy, the Milky Way, has around 150 globular clusters, some of which are out at the edge of the galaxy in the so-called galactic halo, and also near the center, where they travel in highly elliptical orbits around the center.

Open star clusters are not well defined and they usually hang around the arms of the galaxy in the galactic plane. They only have up to a hundred stars that are more widely separated.

Why do astronomers care about star clusters? The reason is simple. They have stars that were born at roughly the same time, which gives us a clue as to how they formed. By studying star clusters, astronomers have made inroads into understanding the life cycle of stars. In other words, they tell us how stars age and how to categorize stars as to population (where they are on the main sequence, which is when they are fusing hydrogen to helium).

A super star cluster is thought to be the beginning of a globular star cluster. Basically, a super star cluster is a region is apace that contains a large number of young, massive stars.

It turns out that every galaxy has a group of globular clusters. They appear to be part of the galaxy formation process because they have older stars populations, stars that have formed after the original massive stars have gone supernova. However, the role of star clusters is still not fully understood. Although many star clusters have stars that are of the same age, this is not universally true, and clusters with different aged stars suggests a much more dynamic formation process.

Globular star clusters tend to have population II stars. Population II stars don't have the metallic elements in their atmospheres like our sun, which is a population I star. This means that globular clusters have aged stars, and these clusters are out at the edge of the galaxy, which suggest that they were captured from other smaller so-called satellite galaxies. There are around a thousand of these open clusters in our galaxy, but astronomers believe that there are many more.

Globular star clusters have very high star densities. This means that the stars are relatively close and may occasionally collide. If nothing else, many of them are involved in multiple star associations, such as binary and ternary stars systems. Astronomers don't expect to find many solar systems in globular clusters because these stars don't contain enough heavier elements to form rocky planets.

Giant molecular clouds, which are produced by supernovae, are where star nurseries are located, and these are thought to be the source of open star clusters. The evidence for this is the fact that open clusters have stars of similar age. These are of interest to astronomers because they are a source of understanding about star evolution. Open star clusters contain stars more widely separated and are only loosely gravitationally bound. This type of cluster contains massive stars that don't last very long, and thus open clusters are short lived.

The main thing to remember about star clusters is that they are part of the star formation process and perhaps even participate in galaxy formation.

Thanks for reading.