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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)
(Score: 3, Interesting) by PiMuNu on Monday April 16 2018, @06:02PM (3 children)
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 2018, @06:32PM
YEAH! THAT'S exactly what I was thinking....
...OOOOOOO, DONUTS!
:)
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
(Score: 0) by Anonymous Coward on Monday April 16 2018, @08:51PM (1 child)
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 2018, @01:58PM
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.