What are collections of galaxies called?
A collection of solar systems is called a galaxy. A collection of galaxies is called ------?
Galaxies are actually not grouped together in quite the same way as stars are grouped together in galaxies. Stars are generally confined to galaxies, with few (if any) existing in the space between galaxies. In general, it's not difficult to determine what galaxy a star belongs to.
With "collections of galaxies", it's a little more complicated. It's not always so easy to determine what group a galaxy belongs to, or even where one group ends and another begins.
Astronomers classify "collections of galaxies" in the following way:
galaxy groups - Groups are sets of just a few galaxies packed into a region that's a few million light-years across.
galaxy clusters - Clusters are sets of a few *hundred* galaxies packed into a region that's a few million light-years across (making them much denser than groups).
There are intermediate cases between groups and clusters, and no strict rule about where you draw the line. It's just like distinguishing between cities and villages. You have to make *some* distinction, but exactly how you define the cutoff is going to be somewhat arbitrary.
I should also add that there are even larger associations of galaxies called "superclusters", which are large associations of galaxies that can extend over distances of more than 100 million light-years. Superclusters contain many groups and clusters in them. But that's as high up as the hierarchy goes. Astronomers don't have any reason to believe that there are larger structures than superclusters.
Get More 'Curious?' with Our New PODCAST:
- Podcast? Subscribe? Tell me about the Ask an Astronomer Podcast
- Subscribe to our Podcast | Listen to our current Episode
- Cool! But I can't now. Send me a quick reminder now for later.
- What is the largest structure in the universe?
- Do galaxies orbit around anything?
- Are there any 'lonely galaxies'?
- How do we know that superclusters are the largest structures in the universe?
- Is the Great Wall the largest galaxy cluster?
How to ask a question:
If you have a follow-up question concerning the above subject, submit it here. If you have a question about another area of astronomy, find the topic you're interested in from the archive on our site menu, or go here for help.Table 'curious.Referrers' doesn't existTable 'curious.Referrers' doesn't exist
This page has been accessed 20019 times since November 21, 2002.
Last modified: June 4, 2003 9:54:14 PM
Ask an Astronomer is hosted by the Astronomy Department at Cornell University and is produced with PHP and MySQL.
Warning: Your browser is misbehaving! This page might look ugly. (Details)