# Moving Stars - Zeta Ophiuchi



## Moonbat (Feb 4, 2011)

Hi, just a question about moving stars.
Now I know that all stars are moving (orbiting around the galactic centre) but it seems that some are moving much faster. See the NASA picture of the day.

Astronomy Picture of the Day

(note you have to look at the 4th of Feb)

It shows a picture of the star Zeta Ophiuchi and states that it is moving at 24 kilometres a second, they believe it was once part of a binary system and was flung out of the sytem when the other star exploded, or imploded or whatever it did to die.

Now my main question is with regards to planets that orbited in the binary system? If (as I think) the other star is gone, then I think that the orbit of Zeta Ophi caused it to fly off in some direction and travel (against the normal flow of the galaxy) across the galaxy, would it have (possibly) taken any of its planets with it?

I'm wondering if it is possible for a star to be travelling through the cosmos with planets, maybe they still orbit it (although I think that is unlikely) or maybe they trail it and orbit each other?

Any one with the knowledge of cosmology have any idea if it could happen? Or would the planets be left in the dark, or destroyed?


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## jojajihisc (Feb 5, 2011)

My guess is the force of an exploding star and/or the acceleration of the remaining star is probably going to be sufficient to overcome the relatively weak gravitational hold any planets have to that star.


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## J Riff (Feb 5, 2011)

Something like this came up once, and the consensus was no, unlikely the planets would follow... but they could. Who can say how many... if our sun took off it may drag Mercury and Venus along, and strand Earth... there's just too many variables to be sure. 
 Certainly any orbit the planet was following previously would be destroyed?.. and therefore any life.


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## reiver33 (Feb 5, 2011)

Using our own solar system as an example;

The sun constitutes around 99% of all the mass in our solar system. Any force acting on the sun, which was capable of moving it from its relative position in space at a significant rate, would have a devastating effect on any planetary bodies.

If they were orbiting in the same plane as the direction of thrust, then (a) a planet between the sun and this force would be hurled into the sun, (b) a planet shielded by the sun from this force would be ‘rammed’ by the sun, and (c) a planet parallel to the run, relative to the force acting upon them, would be displaced at a far higher rate.

Having said that, a _weak_ force acting on the sun, relative to its own effect on planetary bodies (i.e. how it holds them in orbit in the first place), might cause a displacement without a significant distortion in their celestial mechanics.


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## TheEndIsNigh (Feb 5, 2011)

No cosmologist I :-

However, if it was a binary system on one just exploded it would explain the speed. The survivor would continue in a tangential path at the speed it was 'orbiting' the other star.

I suppose we have a similar situation in our local solar system if we consider Jupiter as a failed Sun. If our star (as it will one day) exploded/ceased then yes I think it's possible that the the moons will be dragged away on the path that Jupiter decides it's future lies. The gravitational effect on Jupiter's moons must be negligible that far out so they might not even notice. Well OK but they might not be disrupted too much. There's going to be a bit of a push from the exploding matter but some should survive if if they do get a bit toastier.

However, I suspect that in order for two Suns to both have planets which could support life they would have to be a lot further apart than the Sun and Jupiter are.


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## skeptical (Feb 5, 2011)

The gravity of the parent star is still almost certainly the strongest influence on its planets.   ie.  They will continue to orbit their star.   The nature of the orbit will change.   It is very likely that any potential life on those planets would be snuffed out by the changes, but the planets follow the sun.


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## J Riff (Feb 5, 2011)

For writing purposes... the universe is big enough to hold almost any specific event needed, just don't want to look too bad on the physics end of it.
 A planet is blown up by a supernovae and fifty million years later pieces of it fall on Earth, no need to drag the whole orb along. )


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## Moonbat (Feb 5, 2011)

Thank for the replies.

I did think that the forces involved wouldn't allow any kind of smooth transition, but the star could be moving for millions of years, so if any planets were following they could evolve life after the event.
I agree with J Riff that the universe is big enough for almost any eventuality to occur. So I'm going to assume that it is possible. Also I like the Jupiter analogy, even though the other planets would be left in the dark Jupiter might take some of its moons with it. 



> If they were orbiting in the same plane as the direction of thrust, then (a) a planet between the sun and this force would be hurled into the sun, (b) a planet shielded by the sun from this force would be ‘rammed’ by the sun, and (c) a planet parallel to the run, relative to the force acting upon them, would be displaced at a far higher rate.


 
a) ok so the exploding star would affect the planetary body, but what if the planetoid wasn't exactly in front of the sun (relative to the exploding star) would it be possible that it pushed it away (by quite a bit) and extended the orbit, i.e Mercury would be pushed to an orbit more like Earth's?

b) What if the orbit of the planetoid took it just out of the path of the sun, so the explosion happens and the sun is flung forward (for want of a better direction) but the planet is still orbiting (possibly quickly) and so moves by the time the sun comes past, maybe it gets seared by the proximity of the sun but then follows behind it.

It's an interesting concept.


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## jojajihisc (Feb 5, 2011)

skeptical said:


> The gravity of the parent star is still almost certainly the strongest influence on its planets. ie. They will continue to orbit their star.


 
It depends on the proximity of both the remaining and exploded stars were to the planets as well as their masses. It is definitely possible, perhaps even likely, any planets the star did have are no longer oribting it. 



> there's just too many variables to be sure.


 
Very true.


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## skeptical (Feb 5, 2011)

The variables are important.   However, the majority of binary stars orbit each other at substantial distances compared to the distance a planet is from its parent.  

For example :  Proxima Centauri, which is the closest star to us, apart from old Sol, is part of a triple star system, and orbits at a distance of 13,000 astronomical units from its closest partner.

Earth orbits our sun at 1 astronomical unit.

So typically a binary star system involves considerable separation of the stellar partners.  Not always, and sometimes they can be very close, in rare circumstances.   However, two very close binary partners will unlikely have surviving planetary systems.  Of course, the universe has surprised us before, so I will not claim that to be 100% certain.

However, the strongest probability is a binary system with the two stars well apart, and planets quite closely bound to their parent star.


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## Nik (Feb 5, 2011)

My take, too, Skeptical: Provided the binary stars' separation is enough for the survivor's planets to endure, the planetary system should *mostly* go along.

A couple of gotchas: If there's a kuiper-belt equivalent or a shared Oort Cloud, there could be a meleé of disturbed comets and planetismals: Think 'Late Heavy Bombardment'. (YMMV)
Late Heavy Bombardment - Wikipedia, the free encyclopedia


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## J Riff (Feb 5, 2011)

Good link* Suggests the legendary '5th planet' may have plunged into the sun around the time of the LHB. 
 Jack Hills, I want to live there and study abiogenesis, which really rocks.


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## Stephen Palmer (Feb 9, 2011)

Brian Aldiss did this in reverse in the Helliconia Trilogy.


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## J Riff (Feb 10, 2011)

Yes... the star Batalix and planet Helliconia are captured by the Freyr star system... which loses a sister-star plus a planet and a moon. 
 Another one for the to-read list.


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## chrispenycate (Feb 11, 2011)

All of which doesn't explain why one half of a binary pair would fly off at a tangent if its sister star exploded (even less so if it imploded).

The bodies in a binary system will rotate round their common centre of mass (that's also true of a planetary system, but there the centre of gravity will almost certainly fall within the primary). Should one of them go nova, ignoring the lump which is left, very little of its total mass will convert into energy (well, quite a lot will, but as a percentage it's almost negligible). The mass which is left will, obeying the law of conservation of momentum, have the same proper motion as when it was a star; it'll just be a bit more diffuse. So the orbit of the companion star might wobble a tiny bit, but this is hardly flying off as if the string were cut.

Ignore the electromagnetic shock; the first appreciable change in orbit comes when the matter shock wave (solar wind to the millionth) reaches the second star. It's probably a couple of centuries after the original detonation. Incidentally, it has sterilised the planets on its way through, and probably disposed of their atmospheres while passing. A few megatonnes of matter, with its associated momentum, either hits the star, or is captured by its gravitational attraction. Since the original blast was omnidirectional, it's a tiny percentage of the original outfling, but it's moving very fast, and has an appreciable thrust outward, so our star gains proper motion  away from its ex companion.

But as the shell passes it, while the direction of the centre of gravity of the original star is still as it was, to the second star it has reduced in magnitude, so there is a slight tendency to move still further out, spiralling out either to find a new stability in the elliptic, or drifting off completely. Drifting off, not flung out like somebody letting go of the handle in one of those "whirl the bucket full of water around" demonstrations.

Far more likely to me that a star – or a binary pair – would have drifted at some point in its history too close to a supergiant, and been slingshot round it; a fairly traumatic experience for a planetary system, but not necessarily an unsurvivable one (for the planets, that is. I don't imagine a life form on a planetary surface would have enjoyed it much)

Then again, we're only assuming it's a star, because it's a one pixel point on a photographic plate. It might be a lot closer and the fusion exhaust of an interstellar starship (in which case, if it disappears, it's turned towards us. Worry.) Or, with a really superb optical telescope, turn out to be the nose of a reindeer pulling a sledge…


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## Starbeast (Feb 11, 2011)

*Something huge is moving in space!*

*Hey Moonbat, check out this eerie infared footage!*​


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## J Riff (Feb 11, 2011)

By Jove, that is strange! Any guesses? A Galactic tour bus?


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## Vertigo (Feb 12, 2011)

Excellent post Chrispy I was trying to think how to say exactly what you said! Even though one star exploded the overall mechanical picture is the same and it is hard to believe the shock wave could have been enough to move the star significantly. And surely anything with that much force would have vapourised any planets it encountered.


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## Nik (Feb 12, 2011)

IIRC, a supernova progenitor sheds a large proportion of its mass prior to and during its explosion. This stuff is dispersed above escape velocity, and soon passes any binary or 'common motion' companions to form a growing 'bubble' in interstellar space. 

I'd hope there is a distance beyond which a binary star's heliosphere can mostly block the out-rush, enough to preserve inner planets, such as those in 'goldilocks zone'. Uh, the binary's jovians may have sufficiently strong magnetic fields to take care of themselves, at the cost of fried and/or ablated outer moons...

How the neutrino pulse would affect the dense cores of such jovians, I don't know. Though, given the famous quote that most neutrinos could pass through a light-year of lead (!!), a metallic hydrogen core would seem scant obstacle...

Although the nominal centre of mass of ejecta would remain near the remnant, the expanding shell's influence would be subject to inverse square effects and so the binary  goes tangential ( to first approximation ;- ) probably taking its inner planets along for the ride... 

FWIW, I found several interesting articles; As ever, YMMV.
Shedding Light on Betelgeuse and VY Canis Majoris as Future Supernovae | Gemini Observatory
Betelgeuse - Wikipedia, the free encyclopedia
http://www.lorentzcenter.nl/lc/web/2010/391/presentations/Vink.pdf  {big file}


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