# Multiple star system, stable orbits?

Inspired by worldbuilding SE, I know that there are relatively stable star systems with two or three suns, but any more than that and they start to become very unstable (e.g. trapezium systems), but I'm more interested in the concept of >3 stars, each of similar mass. How could they be arranged in a stable (for a few billion years), non hierarchical manner? I tried sketching out a few possibilities but lack the understanding of how suns interact with each other (heat and pressure being the foggiest elements).

Are there any stable >3 star, star orbits, and if so, what do they look like?

edit to clarify: I am looking for an answer within a single solar system, not a star cluster / galaxy (which would fit the question)

• Well, you can do coreographies as in physics.stackexchange.com/questions/83633/…, but I'm unaware of any results on their stability and I'd be pretty surprised if they're stable. – Emilio Pisanty Mar 27 '17 at 19:26
• @Emilio Somewhat surprisingly, the 3 body figure 8 configuration is reasonably stable to small perturbations of position & velocity. However, it is quite sensitive to mass perturbations: if the masses of the 3 bodies are not identical, Bad Things happen fairly quickly. Sorry I don't remember the exact details, I read the paper (by Cris Moore, IIRC) several years ago. – PM 2Ring Jan 12 at 20:12

Perhaps this isn't the answer you're looking for, but star clusters (particularly globular clusters) and galaxies would seem to fit the bill. Galaxies are a bit more of a stretch since this is probably (1) much larger than what you have in mind and (2) typical galaxies are predominantly made of things other than stars, e.g. gas, dust and dark matter. Globular clusters, on the other hand, are thought to be of predominantly stellar composition. Typical clusters have somewhere in the range of $10^4-10^6$ stars. The clusters are not, strictly speaking, stable - they gradually lose stars - but it takes a long time for them to dissipate completely, longer than the few billion years you asked for. Here is a gratuitous pretty picture of M13, the "great globular":

Generically and qualitatively, the orbits of the individual stars look something like this:

It's easiest to think of the individual stars more like test particles orbiting in a smooth potential - there is no central massive object they all orbit, for instance - but in detail star-star "collisions" (more like close encounters) matter to the evolution of the system.

• I hadn't consider galaxies or star clusters, and you're right in that they do fit my question, however i had intended for an answer within a single solar system, i shall clarify my quesiton – Cursed Mar 27 '17 at 18:52
• @Cursed1701 If you have multiple stars, it's not a single solar system any more. Where do you draw the line? ;) – Kyle Oman Mar 27 '17 at 18:52

If space is not a concern (so no perturbations from the outside) then there should be no limit on the number of stars. Because you can always take a duplicate of your current system place them in orbit of each other far enough apart from each other such that the tidal perturbations can be neglected.

Instead of doubling the number of stars you might also be able to tipple the number of stars, for example by placing the copies into a figure eight pattern.

• This would seem to break the request for a "non hierarchical" solution. – Kyle Oman Mar 27 '17 at 18:53
• @KyleOman hmm, I skipped over that section of the question. – fibonatic Mar 27 '17 at 21:41