The Universe Revealed

Why do galaxies cluster?

Why do galaxies cluster?

A galaxy cluster is by definition a group of galaxies that are bound to one another by gravity. There typically contain 100 to 1000 galaxies and have lots of dark matter and X-ray emitting sources, usually from ionized gas, and they take up a lot of space, typically 2 to 10 million parsecs.

The current thought is that galaxies clustered many billions of years ago because they formed at the same time in the same area of space and just felt lonely enough to come together because they were attracted to one another.

A typical nearby galaxy cluster is the Virgo Cluster, which contains at least 1300 galaxies and possibly 2000. This huge galaxy cluster's center is 53 million light years away. That sounds distant, but as astronomical distances go, it's relatively close.

What's really wild about these galaxy clusters is what is between them. It turns out that it's a hot (30 million Kelvin degrees) rarefied gas in the form of plasma (ionized hydrogen) that emits X-rays. It's mot really clear where this hot gas came from, but it was more than likely stripped out of smaller dwarf galaxies or nebulae.

One of the brightest galaxies in the Virgo group is M98, a spiral galaxy approximately 44 million light years away. This galaxy is an intermediate spiral, which means that it has some barred and non-barred characteristics. A barred galaxy has a an arm that runs through the center.

The largest and brightest elliptical galaxy in the Virgo Cluster is M87. Elliptical galaxies are what most spiral galaxies end up becoming.

What's even wilder is that the Virgo Cluster of galaxies is a member of the Virgo supercluster, which also contains the Local group that the Milky Way belongs to. This supercluster contains around 100 galaxy clusters, and yet it is only one of millions of superclusters in the observable universe.

All of the billions of galaxies in this Virgo supercluster contain hundreds of billions of stars. It's mind boggling, but it illustrates how tiny we are in the scheme of things, and the main thing is that all of the objects in this massive group of galaxies were brought together by gravity and dark energy.

The Virgo supercluster is only an arm of an even larger Laniakea supercluster. Besides the Virgo supercluster, this monster contains the Hydra-Centarus supercluster, Hydra supercluster, Centaurus supecluster, Pavo-Indus supercluster, and the Southern supercluster. The Laniakea supercluster contains nearly 500 known galaxy clusters. Basically, it contains 100,000 galaxies over a distance of 520 million light years.

Surely, there has to be another intelligent civilization in this many galaxies. My guess is that there are millions of them, but they're so far away from us we'll never know that they existed.

Maybe this is the way it's supposed to be. If some intelligent alien species lived nearby to us, we would eventually be involved in a war with them. The immense distance to these galaxy clusters is a way to prevent that from happening.

Thanks for reading.