Superclusters and their galaxies

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Discussion Overview

The discussion revolves around the characteristics and composition of superclusters, specifically focusing on the number of galaxies within them. Participants explore the definition of superclusters, the specific case of the Laniakea supercluster, and the implications of varying estimates of galaxy counts.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions the average number of galaxies in a supercluster, noting that Laniakea has 47,000 galaxies and asks if this is considered large or small.
  • Another participant cites Wikipedia, suggesting that if there are approximately 2 trillion galaxies in the observable universe and around 10 million superclusters, then an average supercluster might contain at least 200,000 galaxies.
  • There is mention of conflicting information regarding the number of galaxies in Laniakea, with estimates ranging from 100,000 to 150,000 galaxies, leading to a discussion about the normalcy of Laniakea's size.
  • A participant highlights the complexity of counting galaxies, referencing the Milky Way's history of consuming other galaxies and noting the discovery of Antlia 2, suggesting that galaxy counts in superclusters may be incomplete due to observational limitations.
  • Another participant reiterates the conflicting information about the number of galaxies in the local supercluster, emphasizing the need for clarity.
  • Discussion includes the hierarchical structure of superclusters, with the Virgo Cluster being part of the Virgo Supercluster, which is in turn part of Laniakea, and how galaxies are grouped by their motion rather than their spatial location.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the exact number of galaxies in superclusters, with multiple competing views on the estimates for Laniakea and the implications of these figures. The discussion remains unresolved with no consensus on the average number of galaxies in superclusters.

Contextual Notes

Participants note limitations in the accuracy of galaxy counts due to observational challenges, such as the "zone of avoidance" caused by dust in the Milky Way, which may obscure parts of Laniakea.

Powehi
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TL;DR
Average number of galaxies in a supercluster
I’ve been looking pretty much everywhere on the internet but I can’t find any answer to this question. How many galaxies are in average in a supercluster ? Knowing that laniakea has 47000 galaxies is it considered as a big or a little supercluster?
 
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Wikipedia:
The number of superclusters in the observable universe is estimated to be 10 million.
Wikipedia:
There are at least 2 trillion galaxies in the observable universe.

So if both quotes are correct then at least 200,000.

Wikipedia also says Laniakea has 100,000 to 150,000 galaxies. So Laniakea is probably somewhat normal.

The Milky way has eaten multiple galaxies. Andromeda and the Milky Way are going to become Milkomeda in a few billion years.
Antlia 2 galaxy was discovered in 2018. The distance is only a few multiples of the Milky Way's radius. That is a good reason to suspect that the number of galaxies in other superclusters is not counted perfectly. Large parts of Laniakea are blocked by "the zone of avoidance" a dusty swath in the Milky Way.
 
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Wiki also says the local super-cluster contains 47,000 galaxies. Seems to have conflicting info then.

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phinds said:
Wiki also says the local super-cluster contains 47,000 galaxies. Seems to have conflicting info then.

View attachment 250252

The Virgo Cluster is inside of the Virgo Supercluster which is inside of Laniakea. The Virgo, Hydra, Centaurus, and Pavo-Indus superclusters all got Plutoed.

This video has some nice pictures. Laniakea is a grouping of the galaxies by motion instead of location. If a galaxy is moving more towards Perseus-Pisces it is in that supercluster. If it is moving more toward the great attractor then it is in Laniakea. It is more like a watershed. Northern Ohio has rivers going to both the St-Lawrence and the Mississippi. You might not expect water in the Allegheny river to be in the same system as water in the Bighorn river but both are flowing toward New Orleans.
 
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