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New Evidence That All Stars Are Born in Pairs

cfa.harvard.edu

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Re: New Evidence That All Stars Are Born in Pairs

#101

Post by astrobe_ »

nsxwolf wrote: post #56
ngoldbaum wrote: post #18

Earlier quoted context omitted.

This is silly semantics. Jupiter and the Sun both orbit the center of mass of the Jupiter-Sun system. The article is making the point that for Jupiter and the Sun this point happens to be just outside the surface of the Sun. It's much simpler to say "Jupiter orbits the Sun" than "Jupiter and the Sun both orbit the center of mass of the Jupiter-Sun system". You can think of the former as a shorthand for the latter.

That's true of all planets no? The Earth and sun orbit the center of mass of the Earth-sun system.

I wonder? If Jupiter has the power to move the Sun, then other planets should be affected to. From this and the fact planet orbits are still said elliptical, I infer that other planets actually also orbit the Jupiter-Sun barycenter. Correct?

Re: New Evidence That All Stars Are Born in Pairs

#103

Post by sdiq »

I know this really isn't the place for religion but somehow the Quran talks about these things:

51:47-49 47. We constructed the universe with power, and We are expanding it. 48. And the earth—We spread it out—How well We prepared it! 49. We created all things in pairs, so that you may reflect and ponder.

And that the universe is actually expanding is something that wasn't known at the time of Mohammad.

Re: New Evidence That All Stars Are Born in Pairs

#104

Post by jobigoud »

nsxwolf wrote: post #56
ngoldbaum wrote: post #18

Earlier quoted context omitted.

This is silly semantics. Jupiter and the Sun both orbit the center of mass of the Jupiter-Sun system. The article is making the point that for Jupiter and the Sun this point happens to be just outside the surface of the Sun. It's much simpler to say "Jupiter orbits the Sun" than "Jupiter and the Sun both orbit the center of mass of the Jupiter-Sun system". You can think of the former as a shorthand for the latter.

That's true of all planets no? The Earth and sun orbit the center of mass of the Earth-sun system.

And that's one of the way we detect exo-planets.

Re: New Evidence That All Stars Are Born in Pairs

#105

Post by bzbarsky »

astrobe_ wrote: post #101
nsxwolf wrote: post #56

Earlier quoted context omitted.

That's true of all planets no? The Earth and sun orbit the center of mass of the Earth-sun system.

I wonder? If Jupiter has the power to move the Sun, then other planets should be affected to. From this and the fact planet orbits are still said elliptical, I infer that other planets actually also orbit the Jupiter-Sun barycenter. Correct?

The planet orbits are approximately elliptical. There are deviations, precisely due to the mass of Jupiter, as well as the other planets. See https://en.wikipedia.org/wiki/Discovery_of_Neptune#Irregular... for a practical example.

To the extent that the planets orbits can be considered elliptical, they orbit the barycenter of the entire solar system, including the Sun, Jupiter, and the other planets. Where that's located relative to the Sun-Jupiter barycenter changes a bit, as the Sun-Jupiter system as a whole orbits around the common barycenter.

But we can make some estimates for how big that offset is. The Sun-Jupiter barycenter is offset from the center of the sun by M_{Jupiter}/(M_{Sun} + M_{Jupiter}) * R_{Sun-Jupiter}, here M_{X} is the mass of X and R_{X-Y} is the distance from X to Y. At aphelion, Jupiter is at 8.16e11m from the sun according to https://en.wikipedia.org/wiki/Jupiter, and its mass is about 9.5e-4 that of the sun, so the offset ends up being about 7.8e8m. The radius of the sun is about 6.96e8m, for comparison (according to https://en.wikipedia.org/wiki/Sun).

OK, what about the other planets? Saturn is about 1/3 the mass of Jupiter and about 2x further from the sun. So its impact on the overall solar system barycenter is about 2/3 that of Jupiter. Neptune is about 18x lighter than Jupiter and about 6x further away, so that's another 1/3. Uranus is about 22x lighter than Jupiter and about 4x further away, so that's another 1/6-1/5. The other planets don't really matter for this calculation with the number of significant figures we're using, because they're both lighter and closer in (e.g. Earth is about 1/316 the mass of Jupiter and 5x closer to the sun, so its impact is about 1/1500 that of Jupiter).

So if Jupiter, Saturn, Uranus, and Neptune all happened to line up the barycenter of the Sun-Jupiter system would be about halfway between the center of the sun and the solar system barycenter. To the extent that they don't all line up, the separation between the Sun-Jupiter and overall barycenters will be smaller. And if Saturn and Neptune both line up on the opposite side from Jupiter, that puts the solar system barycenter pretty close to the center of the sun.

Re: New Evidence That All Stars Are Born in Pairs

#106

Post by bzbarsky »

jansho wrote: post #20
ngoldbaum wrote: post #18

Earlier quoted context omitted.

This is silly semantics. Jupiter and the Sun both orbit the center of mass of the Jupiter-Sun system. The article is making the point that for Jupiter and the Sun this point happens to be just outside the surface of the Sun. It's much simpler to say "Jupiter orbits the Sun" than "Jupiter and the Sun both orbit the center of mass of the Jupiter-Sun system". You can think of the former as a shorthand for the latter.

But doesn't this show that the main players of the solar system are the sun and Jupiter? Apologies for the source, and my clear lack of knowledge in astronomy.

The contribution of Jupiter to the overall solar system barycenter is about the same as that of Saturn and Neptune combined (see numbers in https://news.ycombinator.com/item?id=14576751 ). So I guess it depends on how you define "main"....

Re: New Evidence That All Stars Are Born in Pairs

#107

Post by diogenescynic »

sdiq wrote: post #103

I know this really isn't the place for religion but somehow the Quran talks about these things: 51:47-49 47. We constructed the universe with power, and We are expanding it. 48. And the earth—We spread it out—How well We prepared it! 49. We created all things in pairs, so that you may reflect and ponder. And that the universe is actually expanding is something that wasn't known at the time of Mohammad.

I think that's just confirmation bias (might be another fallacy) because when you have enough source material, it's trivially easy to find those types of references predicting the future or describing something we only prove later. You also end up ignoring all the times the source material was wrong and focusing on the instances it was seemingly correct. See also, Nostradamus and the Bible for a similar type of phenomena.

Re: New Evidence That All Stars Are Born in Pairs

#108

Post by biehl »

pc2g4d wrote: post #32
gpvos wrote: post #5

Earlier quoted context omitted.

Not impossible, but rather unlikely. According to TFA, the partner star was much further out. Also, gas giant planets Jupiter's size are fairly common I thought (this knowledge may be outdated).

TFA? I'm getting "The Force Awakens". Or "Teach For America".

The Fine Article

Re: New Evidence That All Stars Are Born in Pairs

#109

Post by meric »

simonh wrote: post #71
yshdjfhu4irekf wrote: post #59

Earlier quoted context omitted.

is it possible that it's just on an extreme orbit and we may one day reconnect?

We would easily detect a star closer to the Sun than our known stellar neighbours. Any former sibling star further away from us than that would be affected by the gravity of other stars more than by the gravity of the Sun.

How far could the star have travelled in 200 million years? I find it hard to think it could be more than a dozen light years away. And the list of stars within, say, 20 light years, is finite.

Re: New Evidence That All Stars Are Born in Pairs

#110

Post by simonh »

meric wrote: post #109
simonh wrote: post #71

Earlier quoted context omitted.

We would easily detect a star closer to the Sun than our known stellar neighbours. Any former sibling star further away from us than that would be affected by the gravity of other stars more than by the gravity of the Sun.

How far could the star have travelled in 200 million years? I find it hard to think it could be more than a dozen light years away. And the list of stars within, say, 20 light years, is finite.

I think you may be confusing the age of the Sun with the time it takes to complete one galactic orbit.

The sun is more than 4 billion years old while 200m years is a bit less than the period for one orbit of the Galaxy (225-250 my). The Sun has completed more than 20 orbits in its lifetime. Even a 0.1% difference in galactic orbital period between the sun and it's twin would put them 3,000 light-years apart by now.

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