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[Music]

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all right I'm Russell Dietrich I'm a

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student at University of Washington also

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working with the VPL I'm going to be

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shifting gears a little bit and talking

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about larger scale processes in

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particular the triple star system of

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alpha cen and Proxima so in case you

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haven't heard a planet was discovered

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orbiting Proxima Centauri our nearest

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neighbor alright alright I'll move on so

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one of the things that Tom Quinn who's a

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professor at u-dub pointed out right

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away was that Proxima is not alone in

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this image we can see Alpha Centauri a

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and B a little Proxima is circled in

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that with that red circle there it's

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barely visible in this image Proxima is

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about 13,000 au from Alpha Centauri a

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and B for a long time it was unsure

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whether it was gravitationally bound or

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not although new evidence strongly

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suggests that it is gravitationally

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bound we wanted to work from the

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assumption that it is gravitationally

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bound to Alpha Centauri a and B and if

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we assume that then we one of the things

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that we have to consider is that the

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Galactic environment actually affects

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its orbit so in particular this can

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cause close encounters close approaches

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between Alpha Centauri and Proxima and

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we wanted to see how this might be

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effect be able to affect its planetary

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system this was inspired by a study a

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few years back by cabañal and they

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basically took the solar system gas

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giants and the Sun and placed it in a

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wide binary system and one of the things

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that they found is that they these

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galactic forces that I haven't explained

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yet but will in a moment they actually

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drive the system to high eccentricity in

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many cases and cause a disruption of the

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outer planets which of course is a

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catastrophic if you if you are concerned

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about your planets or

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system maintaining nice stable orbits so

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the Galactic forces that I'm referring

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to are to two items the Galactic tides

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and stellar encounters what I mean by

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that is stars that pass within a parsec

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or so of the system galactic tides are

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basically just this idea that it is

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denser close to the galactic mid plane

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and so at a given moment the two stars

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may be different distances from the

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Galactic mid plane and be experiencing

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different gravitational forces and so we

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can think of that as a tide a

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differential force across the system the

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other is forces from passing stars which

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can ski in part or steal a little energy

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or angular momentum from the system

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another thing that I'm going to kind of

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gloss over here but I'm happy to answer

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questions about this idea of radial

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migration that stars don't necessarily

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have to have to stay where they formed

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and we think for for very good reasons

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that Proxima Alpha Centauri did not form

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in their current location so what does

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that actually look like I should also

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mention that in this sort of

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proof-of-concept study we were treating

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Alpha Centauri as as a single mass

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rather than rather than two bodies just

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because of the difficulty of modeling

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the dynamics of those of those bodies of

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the three body dynamics so we we built a

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secular model for the Galactic and tides

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and the stellar encounters and looked at

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many different possible orbits that

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próxima could have started with some of

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these configurations actually will go

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through having these close approaches

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one I'm showing here the distance on the

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right basically this is the a pastor on

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periastron and semi semi-major axis or a

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pastor on periastron of Proxima and

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Alpha Centauri a and B as a function of

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time this is billions of years and then

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the

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it spends a lot of time at high

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eccentricity the dash line refers to

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time of radial migration when it moved

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from its formation location to its

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current location but what you can see in

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this particular configuration is that

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they actually get within a few hundred

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au of each other many of the simulations

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that we looked at actually do this and

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if I actually build some histograms

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based on those simulations what you can

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see here are I've taken the minimum peri

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Center location and all of these

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different configurations and bend them

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accordingly

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according to their initial eccentricity

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semi-major axis and inclination the

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black line here represents

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configurations that never had close

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approaches within 200 au purple our

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simulations where they did approach

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within 200 au orange within a hundred

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and red within 40 and noting that Apple

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Apple Center for alpha sin a and B is

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about 36 au this is actually these

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configurations are actually probably

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destructive to the stellar system in

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addition to planetary systems and so

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we're still trying to understand that

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since we're haven't we're still working

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on models of the three body dynamics

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here but again just treating alpha sin

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as as a point mass we decided to run

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some n-body simulations to look at what

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a close passage does to a planetary

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system and I've modelled several

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different flavors of planetary systems

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one of course is just Proxima be the

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planet that we know about so one of the

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things we want to know of course is how

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does this close approach affect the

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planet that we know about assuming that

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it's the only planet in the system so I

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actually am showing here one simulation

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where Alpha Centauri and Proxima get

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within 4 tau of each other and Proxima B

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starts with a relatively high

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eccentricity and as you can see there's

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not much happening with the

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the semi-major axis a pest Ron or

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periastron or the eccentricity we see a

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little pulse just as the as during the

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close encounter the center of the mass

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of the system is shifting a little bit

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but it quickly relaxes back to its

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original value and so we would say that

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that these close encounters are not

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going to have much of an impact on

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próxima B if it's the only planet in the

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system

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now just shifting to something analogous

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to what Kaiba doll did I took

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solar system gas giants place them at

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their known locations around instead of

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in the solar system around Proxima and

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looked at what a posting post approach

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with Alpha Centauri does to that system

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this is one where alpha and Proxima get

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within 200 au of each other and as you

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can see the the distances of the planets

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that a pastor on semi major axis and

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periastron of Jupiter Saturn Uranus and

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Neptune this is the time of the close

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approach after the close approach to

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Neptune and Uranus actually end up on

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crossing orbits so this is something

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that is really bad for stability of the

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system this is something where we would

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expect one of the planets to get ejected

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or or some other devastating consequence

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yeah so the point is this is actually

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the best-case scenario that I ran for

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this type of extended planetary system

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in most of them one of the planets

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Uranus or Neptune gets ejected almost

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immediately after the encounter but what

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we'll argue based on this is that

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planets that are that if planets ever

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did exist for tens of a you from Proxima

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it this is bad news for them these kinds

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of close approaches so if it did ever

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have planetary systems like this even

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smaller mass most likely since gas

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giants are not as common around M dwarfs

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and these close approaches occurred then

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we would expect that there are but there

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wouldn't be this extended type of

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planetary

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orbiting próxima but of course this has

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the caveat that we didn't model the

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triple star dynamics because it's

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sufficiently complicated this can

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actually modify the effects of close

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approaches this is a test simulation by

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Nate cabe showing what happens if you

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place a tertiary around an inner binary

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without resolving that inner binary you

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can see that it gets within a few

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hundred au but if you actually resolve

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the effects of that inner binary the

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faster precession rate actually shields

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the the tertiary from these close

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approaches and so this is something that

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we still need to consider we're doing

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that in sort of a two-pronged approach

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one is using our secular model and

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modeling the triple star dynamics as a

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quadrupole this shows the effects of the

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adding the quadrupole moment where in

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red this is combining a and B the inner

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binary and then in blue resolving their

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effects in a quadrupole moment and then

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of course the secular approximation

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breaks down so we will still need to

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resort to make caves in body approach

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where necessary so we'll be using this

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to try to map out lots of different

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possible histories of the system of

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Alpha Centauri and Proxima Centauri and

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few questions

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I answered them all I guess great talk o

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me so my mind was floating off to our

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solar system what implications do you

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have for early evolution around the Sun

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does it imply that maybe there was a

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another star nearby from what you did

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for the Sun you know I

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that's a great question I'm not entirely

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sure how to answer that

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knate knate cave is written several

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papers on the motion of the Sun moving

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through the galaxy I think the the

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implication is that the Sun has been

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alone for a long time considering that

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we have this extended system although

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it's I'm not sure that anyone has

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explored yet what effects that may if

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the Sun formed in a cluster and there

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were other stars that were close and the

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Sun was later rejected what effect that

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may have had on sort of the formation of

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the the of the solar system it's an

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interesting Avenue to explore for sure

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yeah hi this is Renee Heller umm so

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given the opposite separation of say

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thirteen thousand au between the a B

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binary and C approxima it gives an

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obligate period of say 100,000 years say

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ten to the sides around six hundred

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thousand is the latest result as a real

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estate six excuse me ten to six years

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the system is tuned to the I don't nine

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years old

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yeah gives ten to the three orbits a

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thousand orbits only since the system

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has been existing so from the planetary

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regime when we consider tides we're

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talking about millions and hundreds of

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millions of years or orbits sure and so

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intuitively I wouldn't guess that

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galactic tides are actually haven't

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actually been effective over say

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thousand orbits of próxima around the a

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B binary so what's actually the effect

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of the galactic tides on the orbital

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evolution as part of your simulation ah

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good question

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so I'm sorry if that wasn't entirely

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clear it's the the galactic tides were

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aren't going to affect clothes things

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like the planets the effect is that it

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affects the it changes the shape of

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Proxima Alpha Sens orbit and so what

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happens is that over long timescales you

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can have some of these close approaches

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or you're right that that there's not

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going to be very many orbits there's a

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thousand ish orbit but it only takes a

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handful

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it only takes a single close approach to

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disrupt a an extended planetary system

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does that answer your question

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I was small one written about the

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collective tides there's a tidal drag of

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the Galactic mid plane as I understood

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its work including models so over a

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thousand orbits I wouldn't expect the

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Galactic mid plane to have a significant

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effect of the orbital perturbation of

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próxima around the binary which is what

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I thought you would include in the model

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oh so the the orbital effects of the of

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the inner binary are small at the at the

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distances that we're talking about of

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and I think I'll bug you in the

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coffee-break again is okay sorry I'm not

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I'm not sure I understand what you're

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asking all right let's think Russell