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Author Topic: What would night and day be like if we lived in a binary star system?  (Read 4090 times)

Alfiestoppani

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Alfiestoppani asked the Naked Scientists:
   
What would night and day be like if we lived in a binary star system?; how would life evolve differently because of this?

What do you think?
« Last Edit: 01/03/2011 02:30:03 by _system »


 

Offline yor_on

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It should be rather chaotic. And I doubt life would evolve, although it depends on how far the stars are from the planet, and each other, as a guess? On the other hand?? Wherever there is water.. or?
 

Offline imatfaal

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Wouldn't the planets rotate around the common centre of mass of the two stars in a fairly orderly manner.  Cannot get my head round the distances involved at present but I will think about it. 

BTW if we lived on a world orbiting a binary system we would be timelords - gallifrey in doctorwho supposedly was around a binary
 

Offline yor_on

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I'm not sure what orbits they could have?
This site have some (need java), but that perfect 8 for example? Would that be impossible?
==

And planets in a retrograde orbit.
« Last Edit: 02/03/2011 18:34:37 by yor_on »
 

Offline imatfaal

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I'm not sure what orbits they could have?
This site have some (need java), but that perfect 8 for example? Would that be impossible?

Well it does happen
http://www.astrobio.net/pressrelease/3659/planets-orbiting-a-binary-system
http://arxiv.org/abs/1102.0508v1

I think the planets will orbit in elliptical orbit around centre of mass - but will read article to see if it helps
 

Offline yor_on

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We need to get FTL working here :)
Or astral journeys.

I want to see them :)
 

Offline imatfaal

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The separation of the two stars in the binary system of NN serpentis is over three orders of magnitude smaller than the orbits of the two planets (0.0043AU , 4.3AU & 5.6AU)

I am pretty certain that this would mean the planets would have a simple elliptical orbit. The paper does not mention any peculiarities of the orbits, it merely gives the semi-major axis; this makes me more sure.

For your reference the sun is 695,500 kilometres in radius which equates to 0.0046 Astronomical Units - so these two stars are unimaginably close
 

Offline imatfaal

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We need to get FTL working here :)
Or astral journeys.

I want to see them :)


Me too
 

Offline Murchie85

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I don't see why there would be a problem here, hypothetically it is possible for a planet to harbour life in this circumstance. If the planets (and other rocks, asteroids etc) are at a suitable distance, they will all orbit round a common centre of gravity much like in our solar system. Actually our sun has an orbit, its just much smaller than the orbits of other planets but it still goes round a centre of mass. The main issue as far as I am aware would be the radiation from the stars, although if they were both sufficiently smaller sub G type stars then the super position of the radiative output could in theory equal that of our star.. minor variations would occur due to there varying distances via the stars respective orbits. In summary factors to consider would be,

•centre of mass(distance from the common point the two stars orbit) I think tightly packed would be preferred. The impact of a looser binary orbit could effect seasons, or create more.
•Star type (so the addition of two smaller stars could have a similar effect to one sun G type star)
•Planet characteristics (so is it the same composition as earth, size, does it have poles?)
•Planetary distance from the centre of mass (closer more radiation problems, further away less energy supply for organisms)
•Moon's if so how many, and would it have a significant effect on tides and planetary "flexing".
•Are there other big bodies such as jupiter's to act as asteroid catchers, to reduce impact frequency on the planet we wan't to encourage life to evolve.

All in all the recipe can still be there for a successful evolution of life.
« Last Edit: 03/03/2011 12:49:46 by Murchie85 »
 

Offline yor_on

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How would the planets magnetic field be influenced by the suns, and its path? Also it's a question of its rotation I think, depending on where it will be in different time segment, relative its suns. But maybe there are perfectly stable paths, giving it the same sort of radiation, angular movement etc? Or maybe life would do fine anyway?
 

Offline Murchie85

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Yes that's a good addition to the list, I think the rotation would be dependant upon the question of whether all the bodies were formed from the same spiral of dust that created the star(s) in the first place. Most likely there were, in our system for example there are not so much extra solar material in comparison to the native stuff such as the planets, asteroids and sun its self.
 

Offline imatfaal

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With one star within the roche limit of the other then you are gonna get accretion and that will lead to some wicked radiation as matter spirals from lighter to denser star. 

On Naked Astronomy they were explaining how coronal mass ejections and other solar phenomena can be caused by violent re-alignments of the solar magnetic fields - can you imagine how much more extreme they would be if the distorting factor was another sun within a million km?
 

Offline Bill S

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Returning to the first part of the O P, the divisions between day and night must depend on the position of the planet with respect to the two stars.  At one extreme the stars will appear close together, possibly even superimposed, in which case there will be a fairly even distribution of light and dark.  At the other extreme the stars will be close to opposite horizons, in which case the periods of darkness will be relatively short.  If the planet's axis is also tilted with respect to the orbital disc, the seasonal pattern could be interesting to calculate.
 

Offline imatfaal

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Bill - that would be correct in a normal binary system, but I am not sure planets could exist in a detached binary.  I have found not evidence for one, and needless to say the three-body problem to determine if it would be feasible is beyond me.  The links I posted above are to a discovered system with two stars and two planets orbiting.  But the stars are only 640,000km apart - so a planet at the same distance as the earth would see two suns almost next to each other (by coincidence separated by a gap about the apparent size of our sun from earth). 

To get a bit poetic - I presume that you would have a first gloaming sunset then a final darkening sunset, and eclipses when the brighter sun is behind the other etc.  But frankly I think any life that we would recognise would have been blitzed by the mad amounts of radiation.
 

Offline Bill S

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Quote
the stars are only 640,000km apart

Would these "suns" not have to be a lot smaller than our Sun in order to exist at this distance apart?
 

Offline yor_on

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Wouldn't that have to do with the orbital speed relative the suns too? To speed up in a orbit you have to slow down as I understands it. Here's a sweet explanation Changing orbits and changing speed. And 'since the orbital speed depends on r, the farther from the Earth, the slow the object goes.' Also I enjoyed reading " it (the spacecraft) is accelerating because it is moving in a circle.' Very true, is it not :)
=

Hmm, don't know what I commented on here, probably just wanted to link that explanation :)
Damna*'n squared :) But, it's such a sweet explanation, you see?
.
« Last Edit: 06/03/2011 14:11:19 by yor_on »
 

Offline imatfaal

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Quote
the stars are only 640,000km apart

Would these "suns" not have to be a lot smaller than our Sun in order to exist at this distance apart?

At least one of them was bigger than the sun before things started to go wrong - the transition from red-giant to white dwarf seems to be the reason they are so close.  Also depends what you mean by exist - they are existing at present, but they are within each others envelope.  This means that the tidal forces will be immense and destructive, that the less dense star has matter that is more strongly attracted to the other star than to itself, etc; ie it won't last long in stellar terms, in human terms is another story.  The angular momentum of the system stops the two stars just falling together - thus they will spiral around each other as portions detach and also start spiralling in.

Quote
With an unusually high temperature of about 50; 000 K for the white dwarf in NN Ser, this event must have happened only about a million years ago. Eventually, the loss of angular momentum due to stellar winds and gravitational radiation will bring the white dwarf and M star into contact, after which NN Ser will become a classic cataclysmic variable (CV)
  from the paper linked above
 

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