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Given all the exoplanet research, has anyone examined the Alpha Centauri system for planets? Any reason why they couldn’t?
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Could any brown dwarf stars be closer to Sol than the Alpha Centauri system, or would we have spotted them by now?
Sure, many people have, but nobody has come up with anything. That doesn’t mean that they aren’t there, though. Current methods can only really detect enormous planets orbiting very close to their stars. We can detect planets that are (a) bigger than Jupiter and (b) closer to their stars than Mercury, but beyond that, its a really tricky enterprise. There are some preliminary (very tentative, don’t go around quoting this as fact) results that might show that Alpha Centauri could possibly have some sub-Jupiter size planets, but it will take years of observation to verify.
Almost certainly not. A brown dwarf closer than Alpha Centauri would be a well-known star, probably visible with the naked eye. Epsilon Indi is the nearest brown dwarf known, about three times as far away as Alpha Centauri, and it can be seen with the naked eye. A closer brown dwarf would probably be even brighter. Even if it were an unusually dim brown dwarf, it would still probably be bright enough to be known at least since the 19th century.
They also get harder to detect the larger the angle between their plane of orbit and our line of site to their star is. Presumably a star could be happily orbiting Alpha Centaur on a plane perpindicular to our line of site and thus never be detected.
Beg pardon? epsilon Indi is a K-class main sequence star. There are no brown dwarfs visible to the naked eye. Heck, there aren’t even any red dwarfs visible to the naked eye: Proxima Centauri has a magnitude of 11, about 1% as bright as it would need to be to be just barely visible. When we do detect brown dwarfs, it’s either by observing the effect on a companion star, seeing it in light reflected from a companion star, or seeing a very young one that’s still shedding heat from its formation in the infrared. If you had an old, isolated brown dwarf, I think the only way you’d be able to detect it at all would be through microlensing, and that takes a great deal of luck.
You’re extremely right, of course. I lazily did a SIMBAD search for Epsilon Indi, and found a visible magnitude of 4.7 (which is naked-eye-visible). I thought this seemed high - should’ve checked closer.
But the brown dwarf in question is Epsilon Indi Ba - it has a magnitude of 24.12 which makes it extremely not visible.
I still maintain that a very close brown dwarf would probably have been detected, though.
If it’s old and cold, it could be within a light year and still be difficult to see even with the best IR telescope.
Keep in mind that although it’s possible, it’s much less likely for multiple star systems to be able to support stable planetary orbits than it is for single star systems.
Do you have a cite? Not on the difficulty, of course, but on the possibility. I don’t doubt you; it just seems like it would a fun celestial-motion case to read about.
(One way might be for the planet to follow one of the suns in a Lagrange point, right?? Is there another?)
There are three ways: You can have a planet in a Lagrange point (which only works if the stars have significantly different masses: The Trojan points become unstable in the equal-mass case), or you can have the stars far apart with a planet or planets orbiting close to one of the stars and essentially ignoring the other, or you can have the stars close together with the planets much further and orbiting the common center of gravity.
OK, though none of those seem that interesting; indeed the first two exist in our own solar system, with Jupiter playing the role of the 2nd sun.
I thought there might be some spectacular figure-eight orbit or some such! (Or perhaps there is such a fancy orbit, but no mathematician has ever stumbled across it? :dubious: )
There are a number of very contrived three-body solutions which all have the flaw that they’re unstable- the slightest perturbation and the planet would go flying off. I wonder if there is in fact some sort of quasi-stable chaotic orbit possible
From the Wikipedia page;
“With the orbital period of 79.91 years.,[28] the A and B components of this binary star can approach each other to 11.2 astronomical units, equivalent to 1.67 billion km or about the mean distance between the Sun and Saturn, or may recede as far as 35.6 AU (5.3 billion km—approximately the distance from the Sun to Pluto)”
In the thread on Binary systems a month or so back, I specifically mentioned this and asked if it was possible to have stable planetary orbits in such a system. Stranger said he’d have to model it, but beyond that I never got an answer.
Well actually question 2 sounds like you’re describing Nemesis. Here’s a link on it
Bump, because I’d love for one of our more Astronomy based Dopers to answer my question about the stability of planetary orbits in that system.
Brown dwarfs will radiate only weakly in infrared and radio frequencies, which at extarsolar distances will disappear into the cosmic background. The only way we could effectively see a brown dwarf is by gravitational influences on the outer planets and KBOs.
[THREAD=580537]Here[/THREAD] is the referenced thread. I can’t find the Matlab script I ginned up a few years back to perform animations of orbital perturbations but that is easy enough to program. I may write a Python script to do it for practice over the holidays if I get bored.
Stranger
Unfortunately, all the cool orbits seem to be unstable.
<mother mode>And if the cool orbits all went and jumped off a bridge, would you do that, too? </mother mode>
No no no.
If all the cool orbits throw their planets out of the system, I suppose you would too, hmmm?
But isn’t it a huge space of possible orbits to analyze? Maybe the stable cool orbit arises only for a particular ratio of the suns’ masses, and/or a particular eccentricity of the suns’ orbit, and/or a particular inclination of the orbital planes.
Perhaps there’s a theoretical reason to expect all “cool” orbits to be unstable. Is there?
Welcome to the world of nonlinear controls theory. My personal bible is Strogantz Nonlinear Dynamics and Chaos which, while not definitive, has a good introductory chapter on the topic of strange attractors, and in particular, Henon maps, which are a visualization tool that allows you to observe the behavior of a complex volumetric function in phase space in a way that is easy (or at least easier) to visualize in two dimensions. This makes it possible to identify, at least in limited sets, what configurations are stable over long periods.
In general, no configuration with four or more bodies that interact with each other are ultimately stable, and only particular solutions of three or more bodies are generally stable. The Sun-Earth-Moon system is stable only because the Moon is within the Earth’s sphere of influence, and because it masses less than 1/25 of the Earth. “Cool” orbits, like figure eight, Klemperer rosettes, and other freaktastic orbits are only stable when there are no perturbative influences; once something introduces a consistent or periodic input into the system it is almost inevitably destabilizing.
Stranger