World set in a Binary Star System - Should I drop the idea?

[Vertigo]

As Chrispy mentions consider Jupiter. I believe it would not have needed to be much bigger than it is now to have "fired up".

However if you are dealing with the two stars having an elliptic orbit about their common centre of gravity then that is not quite a parallel to a a solor system where Jupiter is massive enough to be a binary star. Planets orbiting one star would travel round the elliptic with that star. I think the main issue is just how close they come to the centre of gravity and whether that puts the one star within the diameter of the orbits of the other star's planets:

Imagine a bunch of planets orbiting just one of the stars in the picture above (from wiki - see my earlier post for the link). If the two stars come too close then the planetary orbits could be disrupted. You could even have a situation where one sun "steals" a planet from the other sun as it passes. I guess a lot would depend on how long they remain that close and where the planet in question is at their closest approach. This is why I tend to think it would only be stable if the two stars' separation is quite large and their period of orbit also quite large. This would make it more likely that they never come that close. Though by no means certain, it would depend on just how elliptic the orbits are and how "tight" the overlap of those orbits is.

 

[Glitch]

Without looking at the physics. Having the planet swap between the suns would be interesting for mythology/religion.

If you were to implement a magic system; People's magic could be linked to each sun. One group only being powerful when in orbit of their sun. Of course the hero would be a special person who takes magic from both suns. But I would perhaps only allow the hero to do certain spells under the orbit of each sun; making the hero especially strong at the swap over point; or weak depending on the requirements.

 

[Vertigo]

Not sure any life would survive such a swap unfortunately. If they came close enough for it to happen there's a good chance the planet could get torn apart. Certainly axial tilts would go haywire and it is very unlikely you would end up in the other star's habitable zone.

 

[Glitch]

To keep with believable physics. We could still have ones magic affected by the suns. One group has their magical powers diminished by the proximity of the second star, while the other has it increased. Parts of my first post could still be implemented.

 

[Sapheron]

Bear in mind, as well, that depending on where life and the universe comes from in this story (and as always, magic messes things up) it is possible that everything being stable and able to last billions of years might not be necessary. On a world where gods created everything, the fact that in a million years time the planet is going to crash into a star doesn't come into it unless the story is set in the last few days before the disaster happens.

 

[mithril]

I wrote in my hospital bed a long exposé on the situation, but since I didn't have a computer, it's all longhand, in notebook, and I'm having trouble concentrating on anything now enough to get it typed up.

But note that the "nights of light" would slowly precess round the calendar, from winter through the cycle of seasons until it got back to where it started.

I hope you are feeling better and that it wasn't anything very serious ...

The idea that the 'bright nights' would slowly move over the year is quite fascinating Tell me if I've understood it correctly. Say the year is 400 days long and let's say each season is an even 100 days long. Then if on year 1, the bright nights period starts at day 1 and ends at day 199, then next year it might start at day 3 and end at day 202? I realize that the exact time the period would shift by each year should depend on the period of revolution of the suns so that when one revolution is done, the period of bright nights is again starting at day 1....

 

[TheEndIsNigh]

Vertigo's graphic is excellent however, would that be how it happens in actuality.

I suspect not, He mentions Jupiter. Had it 'Fired Up' it would still be orbiting the sun. There is no need for a mutual elliptical orbit as he shows.

I doubt that Jupiter would have reached critical mass though. Its size is dwarfed by the sun which has a diameter 10 times bigger.

If it were a star, I fancy it would still be hardly more than a pin prick of light given the distances involved which is 4 times that from the sun.

If they were orbiting in such a manner than I wouldn't give a snowball's chance in hell for any planets that orbit them.

The Earth is in a very critical position from the sun with regards to surface temperature. Almost like the three bears in fact.

Is your tale set around Ursa Major by any chance?

 

[mithril]

TIEN - the inspiration for the system was the Alpha Centauri system and as far as I understand, the two stars of Alpha Centauri do revolve around each other in the manner of the graphic provided by Vertigo. The theory is supposed to be that the secondary star doesn't get fired up later but that both stars are formed concurrently. The astronomers have gone on record saying that habitable zones can exist around both the stars. Also that the planets around each star would have stable orbits if they were within roughly 3 AU of the Sun. So I'm thinking that the system would have only a handful of planets relatively close to the sun, maybe as far out as the asteroid belt? Even though no planets have been found in the alpha centauri system yet, they might and that's what I'm taking as the premise for the setting.

Links - solstation

Sapheron, Glitch - I've related the magic system as well the core world religion to the creation myth where I've tried to channel big bang theory a bit. In rough note form it goes like -
Before time had a meaning, God existed as the Primeval Seed. The unimaginable potential inherent in the Seed burst forth at God's Will and so the Universe was born. Its birth was attended by a violent struggle between pure power and pure potential. To bring order out of this chaos, God set forth the laws of the Universe. Thus energy and matter were created. God transformed the left over power and potential into the much safer form of Raw Magic.

So the laws of physics still apply for the most part and unfortunately I can't relate the magic to the two suns in the form Glitch suggested, though that might make a great magical premise with another magic/religion system...

 

[Vertigo]

Vertigo's graphic is excellent however, would that be how it happens in actuality.

I suspect not, He mentions Jupiter. Had it 'Fired Up' it would still be orbiting the sun. There is no need for a mutual elliptical orbit as he shows.

I doubt that Jupiter would have reached critical mass though. Its size is dwarfed by the sun which has a diameter 10 times bigger.

If it were a star, I fancy it would still be hardly more than a pin prick of light given the distances involved which is 4 times that from the sun.

If they were orbiting in such a manner than I wouldn't give a snowball's chance in hell for any planets that orbit them.

The Earth is in a very critical position from the sun with regards to surface temperature. Almost like the three bears in fact.

Is your tale set around Ursa Major by any chance?

TEIN if you take a look here http://en.wikipedia.org/wiki/Barycentre#Barycenter_in_astronomy you can see some other binary star combos (that's where the diagram came from, you can skip the equations and shoot down to the diagrams like I did ). Bear in mind that the distances between the stars in the diagram is much higher than the orbits of the planets, if it wasn't you are quite correct that they wouldn't stand much chance at all. So long as the planets always stay much closer to their own star than the other one you should be OK.

 

[chrispenycate]

I love that animation, but the two stars are equal mass, and equal period, so each reaches the closest and farthest point at the same time. Which is as drastic an oversimplification as my making the second star low enough mass that you could consider it as a superplanet (and setting fire to a Jupiter was not intended as a physical possibility, just an illustration. Unless you have a monolith, of course).
Actually, the centre of gravity would be closer to the larger star, and would wander all over the place (always on the line joining the two, with the same ratio between the distances) as the two bodies hit different portions of their orbit, and the time between the closest conjunctions be thousands of (planetary) years.

If the second star came anywhere near the inner system of the first, even if it was only every hundred thousand years, I doubt whether a planetary system would ever form at all, thus simplifying the problem.

 

[goldhawk]

...would wander all over the place (always on the line joining the two, with the same ratio between the distances) as the two bodies hit different portions of their orbit, and the time between the closest conjunctions be thousands of (planetary) years.

Sorry, Chris, if there are only two bodies in the system, their centre of mass would remain fixed in its inertial frame. It's only when you add more bodies does the centre of mass wander. Also, since the two suns have most of the mass in the system, it won't wander far.

 

[chrispenycate]

Wander relative to that diagram, not in the absolute. It's a pity the set of animations on the Wiki site only gave circular orbits for non-equal masses; it would be nice to have at least one of the bodies more elliptical, and see if the periods do line up that neatly (it has been far too long since I did third order differential equations with no more sophisticated aid than a pencil and block of paper).

 

[goldhawk]

Well, I still think the centre of mass won't wander in an inertial frame. But from what I can remember:

• The ratio of the distances of the two bodies to the centre of mass is constant.

• The ratio of the momentum (mass * speed) of the two bodies is constant.

• Both orbit in ellipses. One focus of each ellipse is at the centre of mass. The other two are in a straight line with the centre of mass and opposite to each other and this line does not rotate.

• Both orbits have the same period, that is, each body takes the same amount of time to complete an orbit.

• Both orbits obey Kepler's Laws.

Of course, if you add a third body, all of this goes out the window.

 

[Sapheron]

I agree with all the points there. They must orbit symmetrically, or else they would be out of line with the centre of gravity, which is impossible, it must remain directly between the two.

As for third bodies, luckily only a third star could have any real effect. Jupiter might cause a slight wobble, at most. Perhaps a particularly large and dense alien spaceship? A nearby but not quite near enough to cause death quite yet black hole?

 

[MstrTal]

So what happens if you build a Dyson Sphere around one of the two stars?

 

[mithril]

It's a pity the set of animations on the Wiki site only gave circular orbits for non-equal masses; it would be nice to have at least one of the bodies more elliptical, and see if the periods do line up that neatly (it has been far too long since I did third order differential equations with no more sophisticated aid than a pencil and block of paper).

I have a link that allows us to vary the masses and some other criteria here. If we put the values of the masses as 1.1 and .9, we should get the type of binary system we are looking for.

Also the solstation link shows the theoretical habitable zones around both stars of the alpha centauri system as they move in their orbits.

 

[Vertigo]

I agree with what's been said above; as far as I understand it, with only two objects in the equation no matter their respective mass they would have to have the same period of roatation about the centre of mass otherwise it simply wouldn't be the centre of mass. Add some more objects like planets and then you get some wobble. That same link of mine shows how the barycenter of the solar system moves; pretty wild really I wouldn't have expected the raltively small mass of the planets to have such a big affect.

MstrTal. If it was a total Dyson sphere then you would theoretically only have the gravitational effects with none of the light/colour ones. However I believe a Dyson sphere still has to radiate huge amounts of heat and I don't know if that would make it visible.

Oh and Mithril that was one wild link I could have spent hours fiddling with that little Java app

 

[MstrTal]

MstrTal. If it was a total Dyson sphere then you would theoretically only have the gravitational effects with none of the light/colour ones. However I believe a Dyson sphere still has to radiate huge amounts of heat and I don't know if that would make it visible.

Cool thanks. I had forgotten about my random thought/ interjection into this thread until I saw the title and when I saw your answer along with some other posts it made me randomly wonder about the materials used in the construction of said theoretical Dyson Sphere.

If it where a Type 2, total sphere, would the added mass surrounding the star from the materials used cause any sort of effect?

I don't know why I am asking other than when you combine this thread with the thread about rotating space craft I suddenly start having the inkling of the beginning of ideas. Ideas for another story idea unrelated to my current WIP and my fingers get itchy.

 

[Vertigo]

My gut feeling is that it probably would based on this:
http://en.wikipedia.org/wiki/Globus_Cassus
I might actually try and find this book to buy; sounds fascinating.

Although that is not a Dyson sphere it gives some idea of the masses involved. Basically the idea is that the earth is completely dismantled and its mass converted into a new hollow sphere with a much larger diameter with the interior surface being the new habitable area. This of course would have no effect on the orbit of the moon or anything else as the mass would be the same. However the new hollow sphere does not have a diameter that even gets close to the surface of the moon. So I guess extrapolating out; to build a Dyson sphere around the sun would probably take the combined mass of most or all of the planets in the solar system and that would, I'm sure, have a significant impact on the dynamics of the solar system.

 

[mithril]

Oh and Mithril that was one wild link I could have spent hours fiddling with that little Java app

And I'm vela enough that I've actually spent many hours fiddling with it The good point is that I think I'll have a much simpler system with near 0 eccentricity than near 0.5 one which the alpha centauri system has... So in that case since the distance between the 2 stars remains constant, the effect on the planet/world should be much more predictable... Let's see where it goes

PS - vela is Hindi slang for which there's no equivalent English word. Roughly means being free enough to indulge in near useless activities without worrying about its cost [it's especially poignant when you should be finishing up the mountain of work that's been assigned to you ]