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Can a triple star have a planet around it ?

  1. May 3, 2014 #1
    can dual star and triple star have planet around it ( possible ? ) . alpha centauri is a triple star right ? is it having any planet around it ? thanks for any response in advance .
     
  2. jcsd
  3. May 3, 2014 #2

    Bandersnatch

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    Sure they can. Have a look at this paper for example:
    S-Type and P-Type Habitability in Stellar Binary Systems: A Comprehensive Approach. I. Method and Applications
    Googling "p-type orbit" and "s-type orbit" will net you more sources and a bunch of pictures to help with visualisation.

    As for Alpha Centauri, this was in the news not a long time ago:
    http://www.nytimes.com/2012/10/17/science/space/new-planet-found-in-alpha-centauri.html
    http://blogs.discovermagazine.com/badastronomy/2012/10/16/alpha-centauri-has-a-planet/#.U2TzC6K0O5s
    ...but then another analysis cast doubts on the discovery:
    http://www.nytimes.com/2013/06/11/s...cast-doubt-on-the-closest-exoplanet.html?_r=0
    http://www.skyandtelescope.com/astronomy-news/no-planet-of-alphacentaurib/

    Here's the paper the latter two articles talk about:
    http://arxiv.org/abs/1305.4960

    So whether Alpha Centauri system actually does have a planet or planets is still unknown. There's certainly little in the way of physics to make it impossible.
     
  4. May 4, 2014 #3
    Those two kinds of orbit are for a planet of a binary star.

    A p-type orbit is what a planet has when it orbits both stars as if they were one object, making it a "Tatooine planet". It is stable if the planet is farther away than about 3 times the average distance between the stars.

    An s-type orbit is what a planet has when it orbits only one of the stars. It is stable if the planet is more than 3 times closer to that star than the average distance between the stars.


    In the Solar System and in multiple-star systems, orbits decompose into a hierarchy of approximate two-body orbits. The same is evidently true of these calculated binary-star planets.

    So for a triple-star system, here are the possibilities.

    Two of the stars orbit each other, and their combined system and the third also orbit each other.

    The planet is much closer to one of the stars than to any of the other ones (s-type).

    The planet orbits the two close stars as if they were one, but is much closer to them than to the third, more distant star (hybrid).

    The planet orbits all three stars as if they were one (p-type).
     
  5. May 12, 2014 #4
    while the scientists are able to spot some of the planets of distant star , why cant they find it out from the closest star alpha cenaturi ?
    i thought alpha centauri was a triple star system , isn't it ?
     
  6. May 12, 2014 #5

    Bandersnatch

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    Yeah, Alpha Centauri is a triple star system, but the third component(Proxima Centauri) is so far removed from the other two that it almost straddles the line between being its own star and being gravitationally bound.

    With the exoplanets, you have to understand what it takes to find one.
    It has to orbit the star in the plane that makes it pass in front of the star as seen from Earth, which automatically means we can't see the vast majority of planets out there.

    Then the planet has to obscure enough of the parent star's light to be noticed among the usual variations in brightness and random noise. This means that the planets that are the easiest to find are large gas giants on tight orbits(you can recognise a repetitive pattern better than a single dip).

    What I'm saying, is that we can't really say that we've 'mapped' a system and found out that there are X and only X planets in it. All we can say is that a planet definitely is there, if we see it.


    By the way, if you're interested in exoplanets, check this site out:
    www.planethunters.org
    It lets you take part in the search by looking at light curves and trying to identify dips caused by planets transiting in front of observed stars.
     
  7. May 12, 2014 #6
  8. May 12, 2014 #7
    Sun, 300 000 times the mass of Earth, manages to permit Moon to orbit Earth with period only 13 times shorter than the orbital period of Earth. There are perturbations - the orbital plane of Moon and the apside line are changing very fast. But Moon manages to keep same inclination to zodiac and same eccentricity all the time, in long term.

    Alpha Centauri components stay at least 11 AU from each other. So a planet could orbit as far as Mars from either star, or both stars might have planets.

    We know that Polyphemus does not exist, or we would have seen it. But we barely see the supposed Bb out of noise, and it is supposed to be only slightly more massive than Earth and on a much closer orbit than Mercury. So a planet with the size and orbit of Earth or Venus around either Alpha Centauri member could easily exist and we would not see it. Or several such planets for each component.
     
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