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posted by martyb on Monday April 16, @04:44PM   Printer-friendly
from the our-biggest-rockets-can't-move-the-earth...-and-here-planets-get...-ejected?!! dept.

Circumbinary castaways: Short-period binary systems can eject orbiting worlds

When eclipsing binaries orbit each other closely, within about 10 days or less, Fleming and co-authors wondered, do tides — the gravitational forces each exerts on the other — have "dynamical consequences" to the star system?

"That's actually what we found" using computer simulations, Fleming said. "Tidal forces transport angular momentum [3m18s video] from the stellar rotations to the orbits. They slow down the stellar rotations, expanding the orbital period."

[...] The expanding stellar orbit "engulfs planets that were originally safe, and then they are no longer safe — and they get thrown out of the system," said Rory Barnes, UW assistant professor of astronomy and a co-author on the paper. And the ejection of one planet in this way can perturb the orbits of other orbiting worlds in a sort of cascading effect, ultimately sending them out of the system as well.

Making things even more difficult for circumbinary planets is what astronomers call a "region of instability" created by the competing gravitational pulls of the two stars.

"There's a region that you just can't cross — if you go in there, you get ejected from the system," Fleming said. "We've confirmed this in simulations, and many others have studied the region as well."

This is called the "dynamical stability limit." It moves outward as the stellar orbit increases, enveloping planets and making their orbits unstable, and ultimately tossing them from the system.

On The Lack of Circumbinary Planets Orbiting Isolated Binary Stars (arXiv:1804.03676)

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  • (Score: 2) by JoeMerchant on Monday April 16, @05:06PM (5 children)

    by JoeMerchant (3937) on Monday April 16, @05:06PM (#667703)

    In the case where Jupiter is a bit larger and starts stellar fusion, then you have the post-2010 Sol system with two suns and Earth still in the Goldilocks zone...

    With short-period binaries as described in the article, aren't they also close enough to go slightly pear-shaped? I mean, that's a clue right there if you're perusing a potential system for habitation, pear shaped suns? Bad.

    • (Score: 4, Informative) by jimtheowl on Monday April 16, @06:07PM (2 children)

      by jimtheowl (5929) on Monday April 16, @06:07PM (#667733)
      Jupiter would have to be quite 'a bit' larger, but more importantly, a lot more massive to start stellar fusion.

      The smallest red dwarf star is about 80 times the mass of Jupiter.
      Under that, we are talking about a brown dwarf unable to sustain hydrogen fusion, but fusing deuterium (2H) and lithium (7Li) instead.
      • (Score: 2) by JoeMerchant on Monday April 16, @07:27PM

        by JoeMerchant (3937) on Monday April 16, @07:27PM (#667762)

        Yes, quite a bit larger to fuse under its own mass, but still far smaller than the sun, like 0.08 solar masses, with a closest approach to earth >4x the distance to the sun, so - significantly larger than it is, but still only pulling on the earth with 0.5% of the pull of the sun.

      • (Score: 3, Interesting) by toddestan on Tuesday April 17, @02:27AM

        by toddestan (4982) on Tuesday April 17, @02:27AM (#667916)

        Actually, Jupiter is about as large as a planet will get. Adding more material to Jupiter would just increase the density without really making the planet itself much larger. Until of course the pressure in the core gets high enough that nuclear fusion starts at which point it becomes a star.

    • (Score: 3, Informative) by takyon on Monday April 16, @06:08PM (1 child)

      These eclipsing binaries mentioned are far closer [] to each other than Earth and Jupiter.

      Also, unless you use some sci-fi magic (like whatever the Aschen did to Jupiter in Stargate SG-1's 2001 []), wouldn't Jupiter need to be many times larger to start stellar fusion?

      [SIG] 10/28/2017: Soylent Upgrade v14 []
      • (Score: 0) by Anonymous Coward on Monday April 16, @06:25PM

        by Anonymous Coward on Monday April 16, @06:25PM (#667746)

        Well, the title of the parent post mentions "Clarke universe", and the body mentions "post-2010", so sci-fi magic is already presumed.

        IIRC, in Clarke's 2010, the Monolith converted Jupiter's core into some high-density unobtainium, which allowed it to collapse enough to ignite the core. The resulting star was very short-lived, since it lacked the fusionable mass that a real star would have, but lasted long enough for the Monolith's purpose.

        The point is -- if my memory serves me right -- Jupiter was ignited by increasing it's *density*, and there was no increase in *mass*, so the gravitational properties of the Solar System in Clarke's 2010 would be unchanged.

  • (Score: 2) by bob_super on Monday April 16, @05:26PM (2 children)

    by bob_super (1357) on Monday April 16, @05:26PM (#667714)

    Silly me has to sell working professional-grade products for a living. Why didn't I go for the jobs where you get to publish computer simulations ?


    • (Score: 1, Insightful) by Anonymous Coward on Monday April 16, @05:33PM

      by Anonymous Coward on Monday April 16, @05:33PM (#667718)

      'Cause academia is a terrible job environment, requires highest qualifications, *and* pays badly?

    • (Score: 2) by JoeMerchant on Monday April 16, @08:24PM

      by JoeMerchant (3937) on Monday April 16, @08:24PM (#667785)

      I think these guys mostly herd undergrads for a living, but also publish simulations and other stuff as PR work for their institution.

      It's a very cliquish club, I lived in a University town for quite a while and considered getting a job with the big brick monument, but without a PhD they'll barely let you mop the floors, and even with a PhD you've got to suck up to the existing old guard to their satisfaction long enough for them to die off before any hope of advancement to a spot where you might get to call some shots on the sucking up yourself.

      My father played the "bounce from institution to institution" advancement game for about 20 years across 6 states until he turned about 64. He's settled down now at the last place for almost 10 years now - tried advancing to department chair when the opportunity came around, but decided that mid-level politics wasn't worth the potential payoff to higher level politics. Now he just hangs around doing whatever he feels like, daring them to fire him because he's ready to go anyway.

  • (Score: 3, Interesting) by PiMuNu on Monday April 16, @06:02PM (3 children)

    by PiMuNu (3823) on Monday April 16, @06:02PM (#667731)

    Just perusing the paper. Fig 1 looks highly suspect to me; what is the statistical significance of the pink band? e.g. between Kepler 1647b and Kepler38b there is another "gap" with width approx 6 days; between Kepler 34b and Kepler 16b there is an even bigger gap (judging by eye).

    I note that their numerical integration uses RK4, which is not symplectic; and therefore suspect for this sort of stability tracking. They do interesting things with transfer of internal angular momentum of the stars to the planets (tidal forces).

    • (Score: 2) by Gaaark on Monday April 16, @06:32PM

      by Gaaark (41) Subscriber Badge on Monday April 16, @06:32PM (#667750) Homepage Journal

      YEAH! THAT'S exactly what I was thinking....


      --- That's not flying: that's... falling... with more luck than I have. ---
    • (Score: 0) by Anonymous Coward on Monday April 16, @08:51PM (1 child)

      by Anonymous Coward on Monday April 16, @08:51PM (#667793)

      They claim that they are conserving total energy and angular momentum to 10E-4, so aren't they satisfying the reason one uses a symplectic integrator to begin with? Given what they are trying to model, my guess is that it would be a pretty complicated Hamiltonian to begin with.

      • (Score: 2) by PiMuNu on Wednesday April 18, @01:58PM

        by PiMuNu (3823) on Wednesday April 18, @01:58PM (#668564)

        I think there are other conserved quantities beyond angular momentum and energy. One can easily write into the equations of motion "conserve angular momentum and energy" without being symplectic.