I was reading about starclusters and superclusters. These terms seem very vague to me. For example how is Laniakea called a supercluster but shapley (which is massive but tiny compared to Laniakea) also a supercluster. And starclusters seems like an even more vague term to me. The definition is a group of stars that are bound by each other with gravity. That would mean that every multistar system is also a star cluster but that is (according to AI) not correct since star clusters have more stars. But I cannot find any exact data on what defines the terms starclusters and superclusters. does it need a minimum amount of stars, does it need to meet a height/width criteria?
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That is one heck of a good question and i have no idea what the answer actually is, but if i was a guessing man i would say that it has to do with the number of stars involved. A handful of stars bound together by gravity is a multi star system. Get to a dozen or more bound by gravity and now you have an open cluster. Get hundreds to hundreds of thousands bound by gravity and you have a globular cluster. Not saying this is the correct answer, but it makes sense to me.
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The diference is in size and structure.
The maximum number of stars in a multistar system is 6 and a starcluster can contain Up to millions of stars.
The distances in multistars systems reaches 1 or 2 light years. An starcluster, tens of light years or more.
A multistar system is born when a Bok globule breaks Up into many protostars bound gravitationally, inside a molecular cloud. A starcluster is created when many Bok globules start to form in a molecular cloud and they are bound by gravity.
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These are great questions! I didn’t study stars very extensively, but here’s my quick take: A multi-star system would be something like the star Castor, which has six stars that were born together at the same time out of the same molecular cloud. Star groups like the Ursa Major Moving Group are small(ish) gaggles of stars that may not have been born exactly at the same time, but did come from the same region of a single molecular cloud. And star clusters are even larger groups of stars that are all generally the same age but not exactly the same age — if you look at, say, a globular cluster, there are stars of many different ages — but are all gravitationally bound.
Superclusters are a sort of different beast, but also sort of similar: They are huge groups of galaxies, not just stars. Admittedly, they’re still stuff that’s clumped together by gravity, but now on a much larger (extragalactic) scale. Again, galaxies come in groups (like the Local Group, a relatively small number of galaxies), clusters (like the Coma Cluster, a lot more galaxies), and superclusters (a cluster of galaxy clusters, so lots and lots of galaxies!).
To your most important point, though, I don’t know off the top of my head if there is a number cutoff, as in five stars is a group but 10 stars is a cluster, etc. If you’re interested in having us find someone to answer this, please email your question to askastro[at]astronomy[dot]com and we’ll try to find an expert to weigh in!
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@aklesman consider this the request to find someone to get us the definitive answer
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Wonderful! To publish it in the magazine (i.e., to be able to officially solicit an answer from a pro), we’ll need a name and location to go with the question. So, whoever feels like it can shoot us an email at askastro or go here and fill out the form at the bottom of the page! Ask Astro | Astronomy.com
Once I’ve got the official question/name/location of someone asking it, I’ll see what I can do!
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@aklesman … Email sent
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Received! I’ll start looking for someone to answer it as soon as I’m able. It’s not always a fast process, but I’m on it.
We may need to break it into two questions (one about stars and one about galaxies), since people who study star clusters generally don’t study galaxy clusters, and vice versa. But we’ll see!
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