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New Evidence That All Stars Are Born in Pairs (cfa.harvard.edu)
165 points by okket on June 16, 2017 | hide | past | web | favorite | 105 comments

> Many stars have companions

Most stars.

Many years ago, i downloaded a copy of the Gliese star catalogue, and set about generating some star charts of nearby space in VRML (which should give you some idea of just how many years ago that was). Multiple stars are listed as multiple entries in the catalogue, and i realised that if i drew markers for each one, they'd overlap and look terrible. Never mind, i thought, there will only be a few of them, and that's alright for a first version.

Not so! The majority of stars were in multiple systems (although the majority of systems are not multiple), and the chart looked even more shonky than i had anticipated. I had to go back and tweak my generator to merge multiple stars into single entries.



This is such a common problem for me today, working on small scale city maps. Hearing about it on a universal/galactic scale, and also in the now redheaded stepchild of earlier web tech (i.e. IE) is not only incredibly cool and impressive (today), but also to hear of the possible data inference implications is somewhat exciting.

oh wow .. VRML. That does take me back

For some background, a little under half of all stellar systems are binaries. About 40% are single stars, and about 10% are triple systems. The remainder (perhaps a few percent) are higher-order systems like quadruples and quintuples.

Could Jupiter have been a failed pair?

It used to be thought that it was a 'failed star', but you’d need at least 75-85 Jupiter masses to get fusion started it turns out so no, it wasn't close to being a star.

No, Jupiter is a planet not a star. Brown dwarfs start out well over a dozen times more massive than Jupiter. Planets form from a proto-planetary disk, as Jupiter did (you can tell because it is in the same orbital plane as the other planets, the same as the original plane of the disk).

99.9% the mass of the Solar System is in the Sun. 0.1% of the mass of the Solar System is in Jupiter. It's very big for a planet in our Solar System but it is very small compared to even the smallest stars.

Related question(s):

Do stars ever look like Jupiter/gas-giant planets at some point during their formation?

Can planets like Jupiter "pull in" enough matter to "ignite" and become stars in the future?

Excluding the Sun, there is not enough mass in the entire solar system to ignite Jupiter. Therefore, barring interaction with another star system, the answer is no.

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).


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

It seems to be a discussion board internet meme. I am not sure of the actual history, but my impression is that it started as "Did you read the fucking article?" which is sometimes rebutted with "Yes, I read the fucking article." and then "read the fucking article" became RTFA and now some people use TFA to mean The Fucking Article. (Or maybe people more polite than me always used RTFA rather than writing it out. I have quite the terrible potty mouth. shrug)

...and RTFA borrows from the older RTFM (which of course pairs with TFM), and "M" indicating the Manual, or rather Instructions Manual, harkening back to the "man" command in Unix.

See: https://en.wikipedia.org/wiki/RTFM

in this context it's usually just intended to mean "the featured article". like "OP" on message boards.

Well, it's the first result on urban dictionary: http://www.urbandictionary.com/define.php?term=TFA

The Fucking Article

I read it as The Feature Article, which looks dumber written out than it did in my head. You know, like Feature Presentation.

The Featured Article. (There are echoes of another F-word in there, mostly from the older abbreviation RTFM, but they are rather faint.)

The Fine Article

"The F…ine Article"

The Feline article?

The Friendly Article, good sir.

The Fine Article

No: https://www.reddit.com/r/askscience/comments/gnq8t/is_it_tru...

The question itself is weird; planets don't really "fail" to become something else. They simply accumulate mass during accretion, and either that mass (and other factors) is sufficient for ignition and sustained fusion, or not.

It would be a little bit like asking if Neptune is a failed Jupiter or Mars was a failed Earth (hmm, perhaps a bad example).

Jupiter is far, far too small to have been a candidate for a brown dwarf.

It does emit more radiation than it absorbs, which is star-like.

But it does so for completely different reasons - gravitational energy release due to gradual contraction rather than nuclear fusion.

Don't think so, it's too small.

Well what do you know, Jupiter doesn't actually orbit the sun! Not properly anyway


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.

Semantics aren't silly in science, nor in education. I don't think it's so uninteresting as to be worthy of ridicule. It is not, in fact, obvious to the layperson that the Jupiter-Sun System would have a barycenter that doesn't lie inside the mass of the sun. The casual mental model (and all physical models I've ever seen) of the solar system we all share puts a metaphorical or mechanical axis through the center of the sun, around which we all the revolve.

What may be a shorthand for you is the obscuring of deeper truth for others, and discovering that deeper truth is a wonderful 'Aha!' moment for those who experience it.

"It is not, in fact, obvious to the layperson that the Jupiter-Sun System would have a barycenter that doesn't lie inside the mass of the sun."

a point doesn't lie in a mass, it lies in closed surface. ;p

someone, somewhere, might have an 'Aha!' moment from that.

You can't make a physical model of the solar system that has the axis outside the surface of the sun because if the radius of sun and planets was in the correct proportion to the distances of the planets, they would be too tiny to see. Nor would you see the microscopic offset of the axis. If the sun was grossly oversized compared to the orbits (as it usually is), then the tiny offset of the center of rotation would still be visually indistinguishable from being at the center of the sun.

Absolutely, I'm not criticising the construction of solar system models. I'm simply pointing out that if you lack a deeper understanding of the system they represent (or don't interrogate your understanding adequately), the simplifications of any model can quickly become understood as truth.

If we are going to be pedantic, it's an N-body problem and we don't know if some planet will be eventually shot out of the solar system.

And the Earth-Moon system orbits their common center, though that center happens to be inside the Earth.

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.

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

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.

All planets orbit the centre of mass of themselves and the local star, modulo interactions with other planets. The position of the centre of mass relative to the surface of the star is completely immaterial.

NB for smaller bodies, Jupiter is involved in perturbing or capturing their orbits to a great extent -- but we could conceivably have several very large planets contributing to that dynamic. Yes, Jupiter is the largest planet.

They are the two most massive, so that is tautologically true...

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"....

A better source than IFLS?

Mostly unrelated, but Nemesis, one of Isaac Asimov's lesser known novels, was one I personally found a good read.

The article says "egg-shaped cocoon" half a dozen times. Does it really mean "elliptical"? It would seem odd for one end of the gas cloud that forms binary systems to be larger on one end. If so, they don't explain why or how.

I read this initially as "paris" and the title took a strange turn when I clicked it

Glad I'm not the only one. I wonder if someone thought that would be a catchy title for this reason.

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.

So we lost our partner? So sad.... ;) I remember reading, nearest proxima century is also a group of stars.

If all stars are born in pairs where is our suns sister sun and earths sibling planet?

From the article:

Based on this model, the Sun's sibling most likely escaped and mixed with all the other stars in our region of the Milky Way galaxy, never to be seen again.

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.

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.

What a sunny day it would be.

Handwavey prediction: we'll detect its location using entanglement within 50 years

I read that as Paris. On the plus side it makes more sense now. Should probably go to sleep...

I also read Paris, and thought "stars" referred to celebrities. Oops

Me too, and i think we discovered a new phenomenon.

OK i ll rationalize it, stars aren't "Born" , humans are. "A star is born" is a common phrase, and doesn't usually refer to stellar objects. Since i was tricked to believe it was talking about humans, it;s easier to understand how i might have confused pairs for Paris (which was also capitalized). Plus i dont wear my glasses.

Good analysis. I was disgusted at myself for taking the Parisian celebrity interpretation, then somewhat consoled but at the same time disturbed that on Hacker News of all places so many people did the very same. But I think you've hit the nail on the head with the title-case Pairs factor. The All Stars expression probably introduced some anchoring too.

Exercise to the reader - use the observed principals to concoct an equally misinterpretable headline.

That is literally the exact thing that I thought too. Its interesting that a sentence like this can be so easily misinterpreted by multiple people in the same way.

The brain has multiple indicators for this misinterpretation. Stars early on in this sentence, narrows down context, Born in makes us even further think of a human star aka celeb, Pairs is capitlized, making us think it is a proper noun, the brain also doesnt read the middle letters of words if you remember that word jumbled experiment where you can still read it. All of this combines together to make the brain on first glance say Paris and not pairs

Isn't it the capitalization of the first characters of each word which causes the confusion?

New evidence that all stars are born in pairs


New Evidence That All Stars Are Born in Pairs

I've never understood the rationale of capitalizing headlines this way anyway (is it the American way?)

Yes, titles of things (including but not limited to visual art, written works, songs) are generally all capitalized except for small words

I also read it as Paris, but correctly interpreted "stars" as celestial. It was a very confusing two seconds.

"All Stars"

Yes, me too.

Me too.


Same here. Paris did some amazing marketing if this is how so many people will read.

I recall the first time I made that mistake: "Must be installed in Paris? Why are these 72-pin SIMMs geo-restricted?"

I read that as All Stars, as in some type of entertainment or sports people.

Maybe not all of them. But quite a few: http://www.imdb.com/search/name?birth_place=Paris,%20France

EDIT: I'm also not sure about baseball all-stars: https://en.wikipedia.org/wiki/Major_League_Baseball_All-Star...

But there have been a number of baseball players from Paris, Texas and Paris, France:



It's because the title capitalized "Pairs" which is not a proper noun, so both of our brains assumed it must mean "Paris".

Last Tango in Pairs

We'll Always Have Pairs

Pairs exist to remind you dreams are real

Damn you. Until the last line I consistently read Paris. Which was the point of course but I wish I'd have paid more attention after misreading the title :D

I want to add another data point to this discussion. I also read that as Paris. return0 has a great hypothesis on this.

the city of light

Even after reading your comment it took me an embarrassing number of tries to read it correctly.

I thought this and made a quick assumption that we found a way to link decoded DNA down to the city level!

I read it 'Paris'. I need some coffee.

Same here.

I believe the effect is similar to that of a garden path sentence[1] except instead of discovering a grammatical inconsistency and having to backtrack to re-parse, the grammatical context misleads the lexical level so much so that we "see" 'Paris' where 'Pairs' actually exists. I suspect that the 'P' being capitalized further supports the 'Paris' misinterpretation.

[1] https://en.wikipedia.org/wiki/Garden_path_sentence

So semantic analysis of born in provides hints to the lexer, turning Pairs into Paris?

I can tell you it gets even more bizarre: I once misread "bluetooth is dead" as "IrDA is dead" and was like, "duh, no shit, Sherlock, how is this even a news?".

So, apparently, everything gets lexed right initially, then it goes to semantic analysis which figures out that some comms standard is dead, obviously IrDA is a comms standard which is virtually dead nowadays, this tidbit is fed back into the parser, which stabilizes on its final output: IrDA is dead. Kill me.

Also, the weird English custom to capitalize most words in titles, but not in normal sentences, adds to the confusion here.

US-English, I think. British-English headlines are less caps-heavy.

I just asked a friend of mine beside me to read it, and she read the same thing, "Paris" instead of Pairs. I also made the same mistake.


I was just going to say the same thing. I need some beer.

I read it as 'Paris' too.

Actually I expect this is a very common error. "Born in $place_name" has a much higher base frequency than "Born in Pairs", so our System 1 brain screams "Paris!" until System 2 kicks in.

For me it was the casing. We aren't​ used to seeing "Pairs" capitalized, especially so since it is not the first word in the sentence. Paris however, will always be capitalized, so the brain autocorrects to the wrong word. Even though the title is in headline-case, it still fools you.

Yep, you hit the nail -- it's the casing, indeed. Much like other humans here, I read it 4 times, and still got stumped until I saw the comments section. (While coffee is next to me, and Paris is almost a stone's throw (3 hr train) from where I live.)

As you could imagine, clicked it purely because of my brain going: "What is that non sequitur at the end of the title?"

Most other news/social media sites have a small picture and/or a blurb to set the context beyond the headline. Since this is not possible here, I'd suggest tags like "Astronomy", "Science" etc. to help alleviate the problem of confusing headlines (pretty sure this has been discussed before, but anyway...)

Me too.. even after 4 rereadings of the title, and then still clicking because wat..

* pours tea

Same. I think it has a lot to do with the fact that in is lowercase and Pairs is capitalized and our mind tried to parse Pairs as a proper noun.

Yes! God damnit brain.

Once AI gets as smart as us, it will likely start to make similar mistakes.

And they will ask for more coffee too.

same here! :)

We'll Always Have Pairs

Yes, there will always be a Paris... city of light!

LeBron James and Steph Curry were born in the same Akron, Ohio hospital, 39 months apart, so I buy the theory.

[1] https://www.washingtonpost.com/news/early-lead/wp/2015/05/28...

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