World With Triple Sunsets

Discussion in 'Astronomy, Exobiology, & Cosmology' started by kingwinner, Nov 10, 2005.

  1. kingwinner Registered Senior Member

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    796
    "NASA Scientist Finds World With Triple Sunsets"
    http://www.nasa.gov/vision/universe/newworlds/threesun-071305a.html

    I have read an article on the NASA web site! It is very interesting!

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    However, I don't totally understand what it is saying in detail, prehaps lacking the background in astronomy and cosmology.

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    Here are some of my questions that I hope somebody who has read the article can answer:

    "The new planet belongs to a common class of extrasolar planets called "hot Jupiters," which are gas giants that zip closely around their parent stars. In this case, the planet whips every 3.3 days around a star that is circled every 25.7 years by a pirouetting pair of stars locked in a 156-day orbit. "
    What is the 156-day orbit referring? The star-pair orbiting around the parent star? The planet orbiting around the parent star? or...? Also, is it really possible to have 2 "suns" orbiting around another "big sun", won't they be called planets because they orbit a star? And is it possible for the 2 "suns" to stick together and kind of like orbiting around each other, as the animation in the web site shows?

    "Previously, astronomers had identified planets around about 20 binary stars and one set of triple stars. But the stars in those systems had a lot of space between them. Most multiple-star arrangements are crowded together and difficult to study."
    Isn't this HD 188753 the first triple-star system with a planet? Why it says here that one set of triple stars with identified planet has already been found previously? On the top of the article it says "The new planet, called HD 188753 Ab, is the first known to reside in a classic triple-star system."

    "Hot Jupiters are believed to form out of thick disks, or "doughnuts," of material that swirl around the outer fringes of young stars. The disk material clumps together to form a solid core, then pulls gas onto it. Eventually, the gas giant drifts inward. The discovery of a world under three suns contradicts this scenario. HD 188753 would have sported a truncated disk in its youth, due to the disruptive presence of its stellar companions. That leaves no room for HD 188753's planet to form, and raises a host of new questions."
    How does this discovery of a triple-star system with a planet contradicts the former theory of hot jupiters formation?

    Does anyone know any web site which provides some background information related to this topic? I would be eager to learn more!

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    Last edited: Nov 10, 2005
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  3. one_raven God is a Chinese Whisper Valued Senior Member

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    How do they know how long a "day" is?
    Can they tell how quickly the plant orbits it's axis?
    I thought they find planets based on star wobble.
    That would only show the length of a year.
    How do they determine the length of a day?
    Did they use a different method to find this planet?
    Am I missing something?

    I don't have time ot read the whole article right now, so I apologize if my questions are answered there.
     
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  5. kingwinner Registered Senior Member

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    796
    Why the articles says "The new planet, called HD 188753 Ab, is the first known to reside in a classic triple-star system" while later it says "Previously, astronomers had identified planets around about 20 binary stars and one set of triple stars"

    So is this the first known system to have a planet within a triple-star system, as the article states?

    Even worse, the Wikipedia says "This star system is only the second triple-star system known to have a planet orbiting it "
    http://en.wikipedia.org/wiki/HD_188753

    Why do they contradict each other?

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    I must manage this because I have to do a report on it...
     
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  7. eburacum45 Valued Senior Member

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    I can't find any mention of a triple star system with a planet or planets apart from HD 188753; however I remember that Hubble once imaged an object orbiting around Proxima Centauri (which was later disproved); so perhaps they are referring to that object. (edit-of course Proxima is a distant member of the Alpha Centauri triple system).
    But this is the only system where the components of the triple star are close enough to interfere with the formation of warm Jupiter-like planets.
    Warm and Hot Jupiters are thought to form in a wide disk of protoplanetary material and then migrate inwards due to friction (or perhaps due to momentum exchange) with the remnants of that disk. In the HD 188753 system there does not seem to be enough room for such a disk and to form.

    Incidentally the 'days' referred to in the article are Earth days, a common measure of time in astronomy (together with Earth Years, and seconds).
    The two companions of HD 188753 A would not look very spectacular from the planet, in my opinion; they would appear several hundred times dimmer than the main star (but still much brighter than a full Moon as seen from Earth).
     
    Last edited: Nov 10, 2005
  8. Lucas Registered Senior Member

    Messages:
    447

    I think that a planet in the triple star system HD 41004 had been discovered before, according to this link
    http://www.obspm.fr/encycl/HD41004A.html

    Note that one of the stars is a brown dwarf
     
  9. DaleSpam TANSTAAFL Registered Senior Member

    Messages:
    1,723
    I liked the article! I didn't know that planets could form around complicated systems like this. Thanks.
    Could it be that a "classic triple-star system" is a specific sub-type of triple-star systems. Perhaps the other planet is around a different type of system. It looks like the classic triple-star is a small binary pair orbiting a larger primary. I don't know what other kinds would look like.

    -Dale
     
  10. Pete It's not rocket surgery Moderator

    Messages:
    10,166
    I think they're referring to Earth days, ie the orbit period is about 80 hours.

    I'm surprised that the planet can survive so close to the star!
     
  11. Pete It's not rocket surgery Moderator

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    10,166
    This is the time it takes for the star-pair to orbit each other.

    No - that's not how the words are used. Planets are not the only things that orbit stars.

    Yep - just like Earth and Moon orbit each other while orbiting the Sun.
     
  12. kingwinner Registered Senior Member

    Messages:
    796
    I am completely mixed up now!
    So is the HD 188753 the first triple-star system with a planet? Does anyone know and would like to share your knowledge?

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    I have found 2 different articles discussing the same issue, but they both refer HD 188753 as the first triple-star system that has a planet in it.

    "It is the first extrasolar planet found in a system with three stars"
    http://www.space.com/scienceastronomy/050713_triple_sun.html

    "First Planet Under Three Suns Is Discovered"
    http://pr.caltech.edu/media/Press_Releases/PR12716.html

    I am just puzzled!
     
    Last edited: Nov 12, 2005
  13. Lucas Registered Senior Member

    Messages:
    447
    I believe that HD 188753 is the first classical triple system harboring a planet, whereas the system that I found is the first triple system found containing a planet.
     
  14. kingwinner Registered Senior Member

    Messages:
    796
    What do you mean by classical triple-star system?

    However, most other articles talking about the same topic refer HD 188753Ab as the "first extrasolar planet found in a system with three stars".


    Edit: Also, brown draft are not normal stars, so I guess it can't be treated as a triple-star system...
    http://www.extrasolar.net/planettour.asp?PlanetID=246 also says it is only a single-star system (the brown draft doesn't count as a normal star)
     
    Last edited: Nov 13, 2005
  15. Lucas Registered Senior Member

    Messages:
    447
    I don't know what's a classic star system, but you offered a link saying that HD 188753Ab is a classic star system. Perhaps a classic star system is a system in which the stars are main sequence stars and /or giant stars. Given that brown dwarfs were firstly discovered in recent years (the first in 1995), mayhaps a system with a brown dwarf is not classic

    Some people will say that brown dwarfs are not stars, but some other say that they are, e.g. look this page
    http://www.wired.com/news/technology/0,1282,57120,00.html

    it's like the debate about if neutron stars and black holes are stars. I don't think that a precise definition of "star" exists right now, it's a bit like the problem that we have to define a planet

    So, in the link that I gave, note that they say quadruple system, but one of the 4 objects cited is the planet, so indeed is a triple star system
     
    Last edited: Nov 13, 2005
  16. valich Registered Senior Member

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    3,501
    You've already read the above and below replies and read the links for yourself that HD188753 is a triple-star system. Certainly it is not "the first," but is the "first" well documented. No need to continue, right?
     
  17. Dinosaur Rational Skeptic Valued Senior Member

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    4,584
    In theory, there are several interesting triple star systems, none of which I would expect to exist in the real universe.

    It is possible for three equal mass stars to orbit a common center of gravity. A circular orbit with the stars always 120 degrees apart is one configuration. Three elliptical paths is another configuration. In the case of elliptical paths, there are three distinct paths. Only a circular path can be shared by all three objects.

    I wrote a Visual Basic program which could simulate a set of objects gravitationally interacting. It indicated decay of symmetrical systems in several hundred to several thousand years. Using 15 digit precision, the initial conditions deviated from the precise values required for such symmetric systems to remain stable indefinitely.

    In the real world, there is no chance that any symmetric system could start up with precisely the initial conditions required for it to maintain symmetry for even a few days.

    Some mathematicians discovered a set of initial conditions which resulted in three objects chasing each other around a figure 8 path. Unfortunately, they were only interested in proving that such a system could exist. They assumed a gravitational constant of exactly one and used one gram masses. I was never able to figure out how to scale their initial conditions to produce a system with realistic stellar masses and the true gravitational constant.

    I do not know if three objects with different masses can form a stable system without two of them orbiting the third. It is obvious that there are two basic systems possible.
    • A System like Earth, Luna, & Sol. The orbits need not be as nearly circular as our system.

    • A system with one object acting as a central mass and the other two orbiting at different distances. For example: A Sol, Earth, & Jupiter system with everything else gone from the Solar system.
    I wonder if other configurations with more complex paths are possible.

    I simulated other symmetric systems. Obviously, you can have N equal mass stars orbiting a common center of gravity (either a common circular path or N distinct elliptical paths). It is possible to have N > 2 equal mass objects orbiting a common center of mass with another object oscillating up and down a line through the center of mass. The line is perpendicular to the plane containing the other objects. I called these Yo Yo Systems

    It was easy to design systems with a dominant central mass and other objects whose paths were in vastly different planes, unlike our solar system in which most of the objects are close to being in the plane of Jupiter’s orbit. Without a dominant central mass, it was difficult to design a stable system unless all the objects were in the same plane (or nearly so). Some object seemed to get ejected sooner or later. Perhaps if I left such systems run for days, none would remain stable.
     
  18. orcot Valued Senior Member

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    2 of the stars orbit the the other star.
    The triple system is somwhat plain but the main star is a g type star yust like our own sun. And it's about 5.6 billion years old, so according to age and status it's yust like our own sun.
    The other fact is that the two other suns circle at aboud 12 AU that's less far then uranus is from the sun, that's close and because of their gravitationally pull the G type orbit path should become unstable afther 1.3 AU. That planet is wel within that distance but their are quistions on how that planet could have formed from so little material.
     
  19. Dinosaur Rational Skeptic Valued Senior Member

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    4,584
    I think Asimov wrote an article (not SciFi) which specualted about a binary system with a planet orbiting one of the stars. He claimed that from the planet, the other star would not seem like Sol. It would appear to be merely the brighest star in the night sky.

    I do not remember the details of the article, but assume that a planetary orbit would not be stable if the other star was close enough to seem like Sol rather than a very bright star.
     
  20. orcot Valued Senior Member

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    3,414
    The Mean Angular Star Size
    of earth at 1 AU is 0.531°
    at uranus 20AU it's only 0.027°

    So it get's 20 times smaller. So yes a compagnion star within a couple of AU would look pretty dim in compared.
    Actually from a planet around alpha centauri a or b. You proberly couldn't even see proxima centauri (the 3de star) with the naked eye.
     

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