Multiple Sun Planetary System

[ParanoiA]

Is it possible for a planet to orbit a "group" of stars?

 

Seems like I remember some sci-fi I read as a teenager that involved a planetary system with multiple suns. It seemed to make sense at the time, but now that I've enjoyed a little popular science in my life, not that I understand it really, it seems like it wouldn't be possible.

 

So, what gives?

[Sisyphus]

It's possible (they've actually found some), although not in all cases, and the number of orbits it can have is limited. You, can, for example, have planets orbiting just one of the stars in a binary system, or multiple stars at a much greater distance than the stars are from one another, but not like a "figure eight" or something.

[ParanoiA]

Cool. Hmm..I guess I didn't think it was possible for stars to get too close together without their respective gravatic forces locking them in orbit together - or whatever they call that. (I remember seeing it on the science channel or something but I don't remember).

 

So, basically it's possible for a group of stars to sort of...uh, form a "virtual" single source of gravity for a planet to then get locked into? That's how I'm picturing it anyway. A ball of stars, as if they were one big star.

 

Of course, I guess you have to consider how hot that planet is going to be. I don't suppose you could get a distance away that would give you the same effective result as Earth's one sun...

[ecoli]

Seems like I remember some sci-fi I read as a teenager that involved a planetary system with multiple suns

 

Tatooine (from star wars) has two suns.

 

Cool. Hmm..I guess I didn't think it was possible for stars to get too close together without their respective gravatic forces locking them in orbit together - or whatever they call that. (I remember seeing it on the science channel or something but I don't remember).

 

So, basically it's possible for a group of stars to sort of...uh, form a "virtual" single source of gravity for a planet to then get locked into? That's how I'm picturing it anyway. A ball of stars, as if they were one big star.

 

Of course, I guess you have to consider how hot that planet is going to be. I don't suppose you could get a distance away that would give you the same effective result as Earth's one sun...

 

Wouldn't the planet orbit around the binary star system's center of mass?

[Klaynos]

Our solar system is relatively unusual, the majority of solar systems that we've looked closely at have been binary systems which by definition have 2 suns.

[ParanoiA]

No kidding. I had no idea. How about more than two?

[Klaynos]

No kidding. I had no idea. How about more than two?

 

I'm sure sure if we've discovered any tri-star systems... There's none that I'm aware of, and they were not mentioned in my course on stars.

[D H]

Tatooine (from star wars) has two suns.

 

Funny you should mention Star Wars ... From Ask an Astrophysicist

The Question

Binary stars are popular in science fiction. Star Wars' Tatooine' date=' for example. I'm wondering about the orbit of a planet around binary stars. Is it possible?

[b']The Answer[/b]

There are stable orbits for planets in binary star systems. There are various stability criteria which say when an orbit is stable. One such criteria (and I don't know the actual numbers) says that if all orbits are circular and the stars are the same size, then the planet must orbit one of them at less than /some fraction/ of the inter-star distance, or must orbit both combined at more than /whatever/ times the inter-star distance. Figure-eight orbits are unstable, and can eject the planet from the system.

 

Wouldn't the planet orbit around the binary star system's center of mass?

No. There is no attraction toward the center of mass, only to the two stars individually.

 

One scenario for planetary formation in a binary system is a wide binary system -- a pair of stars orbiting each other at with tens of AUs between the stars (e.g., the Centauri system). Planets can form close to one of the stars and remain in relatively stable orbits for quite some time. As an analogy, think ofJupiter being a star and its moons being planets.

 

The other scenario for planetary formation in a binary system is a close binary system -- a pair of stars orbiting each other at fractions of an AU. Planets can still form, but only at some distance from both stars. The stars will distort the orbits of close-in planets significantly; Kepler's laws will not hold in such a system.

 

A paper: http://www.astroscu.unam.mx/rmaa/RMxAC..22/PDF/RMxAC..22_lissauer.pdf

[Sisyphus]

Cool. Hmm..I guess I didn't think it was possible for stars to get too close together without their respective gravatic forces locking them in orbit together - or whatever they call that. (I remember seeing it on the science channel or something but I don't remember).

 

Well sure. That's what a multiple star system is: stars orbiting one another.

 

So, basically it's possible for a group of stars to sort of...uh, form a "virtual" single source of gravity for a planet to then get locked into? That's how I'm picturing it anyway. A ball of stars, as if they were one big star.

 

Well, sort of. That would be the close to the case with two stars closely orbiting one another, and a planet distantly orbiting them both. It's still the individual stars' gravity, though.

 

Of course, I guess you have to consider how hot that planet is going to be. I don't suppose you could get a distance away that would give you the same effective result as Earth's one sun...

 

I don't see why not. Stars are all different sizes and temperatures, by many orders of magnitude. Why not two half-suns? Or two suns, with the planet farther away?

 

One problem you would have though is temperature variation. Earth doesn't have a very eccentric orbit, and is always pretty close to the same distance from our sun, relatively speaking. With multiple stars, on the other hand, I think it's pretty inevitable that you'd be getting nearer and farther away from each of them much more dramatically.

 

No kidding. I had no idea. How about more than two?

 

Yup. According to Wikipedia, we've discovered up to six.

 

http://en.wikipedia.org/wiki/Multiple_star_system

[ParanoiA]

One problem you would have though is temperature variation. Earth doesn't have a very eccentric orbit, and is always pretty close to the same distance from our sun, relatively speaking. With multiple stars, on the other hand, I think it's pretty inevitable that you'd be getting nearer and farther away from each of them much more dramatically.

 

That makes sense. But is it possible for the conditions to be just right so that a planet could orbit a multiple star system and be relatively stable in terms of temperature, climate?

 

Yup. According to Wikipedia' date=' we've discovered up to six.

 

http://en.wikipedia.org/wiki/Multiple_star_system[/quote']

 

That's very cool. I don't know why I didn't look that up myself, wikipedia is usually my first quickie source.

 

The way these star systems work is fascinating, and confusing. A binary pair in a distant orbit of two closer binary pairs? I just don't grasp gravity and spacetime enough to have imagined such a scenario. Or the two triple systems in orbit together with a single star. Crazy.

 

So...for the sake of discussion, let's just say I'm working on a little fiction piece for fun. And I need a plausible system of 9 "suns", and at least one stable planet to support life. I put suns in quotes because it could even be the illusion of 9 suns - an effective result. Is that just an outright impossibility? Or could I actually study this subject area enough and come up with my own system that is at least "possible", in the fiction sense?

[Sisyphus]

I think that can be done, but it might be tricky. You can definitely have a stable nine-star system (improbable, but nothing fundamentally wrong with it) and put a planet in it, but I'm thinking the requirements for the stable configurations would mean that some stars would be have to be many times farther away than others, and so they wouldn't really all have the same status to someone on the planet. I'm not sure, though, Maybe something with very different stars, from white dwarfs to supergiants, perhaps an extremely unusual "planet" of some kind, depending on how exotic you're willing to get. Sounds like a problem Larry Niven would enjoy.