Posted on by Tammy Plotner

New Planetary System Has South African Astronomers Doing A Double Take

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Double your pleasure… Double your fun… Double twin planets found orbiting a double sun! Are you ready for the weird, true and freaky? Then check out what Drs. Stephen Potter and Encarni Romero-Colmenero from the South African Astronomical Observatory (SAAO) and their colleagues have found. It would appear there’s evidence pointing towards the existence of a double planetary system where a pair of giants are at home orbiting a binary star.

Known in polite social circles as UZ Fornacis, this eclipsing double star is anything but a friendly environment for a solar system. Because the pair orbits so closely, the white dwarf never stops collecting material from its red dwarf companion. This steady flow gets superheated to millions of degrees and produces copious amounts of deadly x-rays. This pair of twin stars are so small they would fit within the radius of our Sun and orbit each other within a period of hours. Because of their eclipsing nature, Dr. Potter and his collaborators were quick to notice that the periodic timing wasn’t regular. This evidence led them to theorize a pair of planets needed to be present to account for the wobble and to infer that the masses of the two planets must be at least 6 and 8 times that of Jupiter and take 16 and 5 years respectively to orbit the two stars.

“The two planet model can provide realistic solutions but it does not quite capture all of the eclipse times measurements. A highly eccentric orbit for the outer planet would fit the data nicely, but we find that such a solution would be unstable” says Potter, et al. ” It is also possible that the periodicities are driven by some combination of both mechanisms. Further observations of this system are encouraged.”

This discovery was made possible by new SAAO and Southern African Large Telescope (SALT) observations combined with archival data spanning 27 years, gathered from multiple observatories and satellites.

Original Story Source: South African Astronomical Observatory News.

26 Replies to “New Planetary System Has South African Astronomers Doing A Double Take”

  4. I think some theories on the nature of stellar systems just went through the paper shredder.

    LC

    1. In all fields of science, the correct term to use is hypotheses; they only become theories once they have passed stringent tests.

      1. That is true, but it is also common to talk about theories before they are completely tested, such as Higgs theory or string theory.

        LC

    2. Which ones? The system is of almost surprising similarity to some other systems (see my comment above) detected earlier. I think that, to the contrary, this similarity will probably spawn a few new ideas regarding circumbinary planets and their formation.

      1. From what I understand there are models of stellar system evolution which prevent the formation of planets around such double stars.

        LC

      2. Not around double stars in general. It all depends on the distance of the planet, and the two stars. IIRC, if D is the distance between the two stars, a planet can orbit at a distance R if R 5 D. Such common-enveloppe eclipsing binaries have typically periods of hours, so 5 D isn’t really that far out in the system. The sun could probably be an eclipsing binary and still have all its planets…

      3. Not around double stars in general. It all depends on the distance of the planet, and the two stars. IIRC, if D is the distance between the two stars, a planet can orbit at a distance R if R 5 D. Such common-enveloppe eclipsing binaries have typically periods of hours, so 5 D isn’t really that far out in the system. The sun could probably be an eclipsing binary and still have all its planets…

      4. Not around double stars in general. It all depends on the distance of the planet, and the two stars. IIRC, if D is the distance between the two stars, a planet can orbit at a distance R if R 5 D. Such common-enveloppe eclipsing binaries have typically periods of hours, so 5 D isn’t really that far out in the system. The sun could probably be an eclipsing binary and still have all its planets…

      5. Not around double stars in general. It all depends on the distance of the planet, and the two stars. IIRC, if D is the distance between the two stars, a planet can orbit at a distance R if R 5 D. Such common-enveloppe eclipsing binaries have typically periods of hours, so 5 D isn’t really that far out in the system. The sun could probably be an eclipsing binary and still have all its planets…

      6. From what I understand there are models of stellar system evolution which prevent the formation of planets around such double stars.

        I believe I’ve seen you say that a couple of times; no references given. A priori that would be a reasonable expectation, and my old (2006ish) astrobiology books doesn’t say much in that regard.

        However, when out of raised curiosity I try to browse the web, I get the picture that modern simulations (here: later part of -00) contradicts naive ideas:

        “A few years ago, it was thought that [binaries] were a very bad site to search for planets,” says Michel Mayor of the Observatoire de Geneve. “So we carefully eliminated all binary stars from our sample.”

        But planets may be just as likely around binaries as around single stars. Recent numerical simulations have shown that Earth-like planets, known as terrestrials, form readily in double star systems.

        “The most significant thing we found is that terrestrial planets around certain close and wide binaries can look similar to planets around a single star,” said Jack Lissauer of the NASA Ames Research Center. …

        “All of our simulations have been able to form terrestrial planets,” said Ames researcher Elisa Quintana, who presented a poster on these results at the symposium.”

        Further, arxiv 0705.3441 seems to say double stars can be as good for planetary growth as having giants in the system:

        “The distribution of final terrestrial planet systems in the aforementioned cases [wide binary] is quite similar to that produced by calculations of terrestrial planet growth in the Sun-Jupiter-Saturn system.

        In contrast, terrestrial planet growth around a star lacking both stellar and giant planet companions is slower and extends to larger semimajor axis for the same initial disk of planetary embryos (see Figure 12 in [7]).”

        And the same paper give some numbers on expected systems:

        “… ~ 40 – 50% of binaries are wide enough to allow both the formation and the long term stability of Earth-like planets in S-type orbits encircling one of the stars. Furthermore, approximately 10% of main sequence binaries are close enough to allow the formation and long-term stability of terrestrial planets in P-type circumbinary orbits ([16, 11]). Given that the galaxy contains more than 100 billion star systems, and that roughly half remain viable for the formation and maintenence of Earth-like planets, a large number of systems remain habitable based on the dynamic considerations of this research.”

        I don’t know if that is a reasonable picture of the current status of knowledge regarding planetary formation, but at least it is problematic for what you say. (No more than the current data is, of course. =D)

      7. I am just recalling a few general articles in SciAM, which are from some years past. This is not an area I tend to research or study.

        LC

      8. I play around with a gravity simulator called Universe Sandbox and have easily made gravitationally stable planets around binary stars in those simulations. However, it doesn’t simulate formation of the planets so it’s obviously not a perfect nor anywhere near complete test.

        My current favorite simulation has 2 sun-like stars with 4 planets each (with each having an Earth in the habitable zone…which is extended due to the twin suns. They have identical years, which I think is equal to something around 1.3 or so years) Further out I have some gas giants and such that are circumbinary with a few moons each and some random long and short period comets (though a good deal of those comets will probably be flung out soon as I didn’t really plot their orbits so much as just fling them out there) . I did have to create a large dusty debris field to better observe the interaction of the 2 stars (makes a rather pretty figure 8) and to be fair, the simulation has only run for maybe 10,000 years…but in that time the orbits of inner planets have been very stable to their respective parent as well as the outer planets being stable to the binary as a whole. I forget the exact details, but I believe the stars are 10AU apart with the furthest non-circumbinary planets being at about 3-4AU. The circumbinaries start at about 12AU from the barycenter (about 7AU from either star at closest approach respectively). I cannot speak well for their stability as all except the inner-most haven’t completed very many orbits due to the massively increasing orbital time frames from extended distances. I’m not even sure if I remember that my Pluto+Charon have made more than a single orbit during the simulation so far as, if I remember correctly, I think I have them out somewhere between 100 and 150AU.

        Anyway…I’m rambling…but it’s a fun thing to mess around with to see how alien solar systems could be laid out. Some have even used it to prove that their favorite fictional solar systems are completely bogus and would fly apart 🙂 The guy that is making it plans to update it with more features as he is able to.

      9. I seem to remember a UT article that discussed this topic(Earth- like planets forming readily in binary systems), but I may be mistaken. In any event, I always welcome more articles and information with respect to extrasolar planets and their stellar systems.

  5. “Double *twin* planets”? I don’t see that in the original news story. A twin planet (i.e., two planets orbiting each other, and at the same time orbiting a star – or double star, for that matter) would indeed be something completely new. But here, the two planets are definetly not orbiting each other. They orbit the red dwarf / white dwarf couple in 5, and 16 years, separately. Planets orbiting double stars is not a completely new thing, and even two planets orbiting a double star is not new: HU Aquarii and NN Serpentis are two such systems of eclipsing binaries with two planets that can be found in the Extrasolar Planet Encyclopedia. It is the first system where two planets orbit an eclipsing binary pair where one member of the pair is a white dwarf, though.

  6. “Double *twin* planets”? I don’t see that in the original news story. A twin planet (i.e., two planets orbiting each other, and at the same time orbiting a star – or double star, for that matter) would indeed be something completely new. But here, the two planets are definetly not orbiting each other. They orbit the red dwarf / white dwarf couple in 5, and 16 years, separately. Planets orbiting double stars is not a completely new thing, and even two planets orbiting a double star is not new: HU Aquarii and NN Serpentis are two such systems of eclipsing binaries with two planets that can be found in the Extrasolar Planet Encyclopedia. It is the first system where two planets orbit an eclipsing binary pair where one member of the pair is a white dwarf, though.

  7. Yo Tammy, there is also a double occurrence of the preposition “to” in the eighth line of the second paragraph: “… to account for the wobble and to to infer that…”

    1. Likely the stream of material getting sucked off the red dwarf to the bigger star.

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