Planet with 3 suns!

[GOLLUM]

Thanks for the update Stalker....

 

[ommigosh]

Good explanation Stalker, thanks.

I think I saac Asimov wrote a classic science fiction story called Nightfall about a planet with multiple suns. It was always daylight there apart from every few thousand years or so when the suns all fell below the horizon together causing mass panic, riots and the sudden collapse of civilisation.. A good idea for a story, and I always trusted that Asimov was probably a good enough scientist to have worked out if such an arrangement of suns was possible.

 

[Arkangel]

Stalker, I have a question. Wont the gravitational pull of one sun affect the other. Eventually one as to win over the other or their mass have to be identical. If it is a elliptical orbit wont the gravity pull of the bigger mass star be more at the closest point between the 2 and the one with higher mass pull on the other. If they have to be stable shouldnt they have a circular orbit.

 

[dreamwalker]

Stalker, I have a question. Wont the gravitational pull of one sun affect the other. Eventually one as to win over the other or their mass have to be identical. If it is a elliptical orbit wont the gravity pull of the bigger mass star be more at the closest point between the 2 and the one with higher mass pull on the other. If they have to be stable shouldnt they have a circular orbit.

Thats like 4 questions!

Wont the gravitational pull of one sun affect the other. Eventually one as to win over the other or their mass have to be identical.

This could happen but it's much more complicated than that. Let me explain.
If a red giant was orbiting a neutron star - (a big massive marshmellow of a star orbiting a tiny lead ball) in a very tight orbit close enough for the neutron stars gavity well to be greater than the force of gravity near the surface of the red giant, then matter may transfer from one star to another. but this would cause problems, because nuetron stars burn different fuel at a different rate to a red giant. Either star could become unstable and there orbits could become unstable. One star could nova, or the red giant could super nova. the Nuetron star could (and most probably over time) turn into a black hole as there super dense already. But the key for that to happen is that one star has to be dense and the other has to be puffy.

If it is a elliptical orbit wont the gravity pull of the bigger mass star be more at the closest point between the 2 and the one with higher mass pull on the other.

Not sure on exactly what you where trying to say but...
Its the same away jupiter doesn't effect the Earths orbit. Elliptical or not. In a complete cycle there'll always be farest from and closest too distance and the (comparitivly weak) gavitiational forces will be ballanced because the whole thing is in a closed system. It would take something from out of the closed system to upset the balance, eg rouge planetoid from outsie the star system to upset the gavitational balance.

If they have to be stable shouldnt they have a circular orbit.

No. - Stable means the orbits don't degrade after some time. Comets like haleys have highly elliptical orbits but are (almost - they keep losing mass) in stable orbit. So is pluto - its in a very elliptical orbit considering its a planet.
After 5 billion years, you can be pretty much certain that everything you see in the solar system is in a stable orbit - so far as to say it hasn't escaped the solar system or been swallowed up.


About gravitational fields. It works on (nearly) the inverse square rule. Which means, on the surface of earth gravity is 1, travel 2 away from it and gravity will be a quarter, travel 5 away from it, gravity will be a 25th. So you need to be relativily close for gravity to grab you! Conversly, you'll never be out of the gravitational effect of an object no matter how far away you are.


Another thing. Were the common orbit center is close to the center of the largest star;
If they where near equal and the orbits stable, then there orbits center would be inbetween all three stars, and there orbits would never be the same twice. Its long been said that when there are 3 or more objects in an orbit, it becomes impossible to calculate any exact figure in relation to there orbits.

(I used to play astronaut)

 

[Arkangel]

Thanks for answering dreamwalker

 

[Stalker]

but this would cause problems, because nuetron stars burn different fuel at a different rate to a red giant.

AFAIK, neutron stars don't burn at all, they are the product of incomplete collupse of the star that has exhausted its fuel, so intertal outward pressure cannot balance its gravitational inward pull but gravitation is not enough to transform them into black holes. Such neutron star does not emit any rays, at least, in visible diapason. But, you are right such examples of neutron star-giant were observed, and astronomers fixed pumping the substance from the unfortunate giant that appeared to orbit the main component too close by to the neutron star.
To another point, well... if I understand you right, you are talking about prolonged elliptical orbits. In this case, yeah, such an orbit is more unstable that that one which approaches more rounded ellipse.
On all other points I agree completely with dreamwalker.

 

[dreamwalker]

^^Yeah the nuetron star was just one example (poor one now I realise it) of a small super dense object that wasn't a black hole. I probably have to reseach whether they burn with nuclear fusion or not but im pretty certain some energy is emmited or else it would collapse and form a black whole due to density issuses.

As for orbits. My general understanding is...
It goes around = stable
It sprials = its unstable
the inverse square law that governs gravity allows stablity in orbits to be suprisingly easy although in reality, no orbit is truely stable over forever due to stellar friction and objects losing and againing mass- even within a closed system.
But hey astronomys all about sitting on your ass generalising anyway so!