OK, in a comment David pointed me at a web page about a theory that we have some kind of “binary companion” star lurking nearby. Supposedly there are “issues” with the present orbits of some objects in our solar system that just don’t “add up” and the precession of the equinoxes is a bit of an issue as it happens relative to stars, but not as clearly relative to objects inside the solar system (the idea being that it is an artifact of the whole solar system moving, not just the pole of the Earth wandering around).
Looking into this some, there ARE issues with those things. Exactly how much was not clear on a cursory (couple of days ;-) look. But there’s something ‘not right’ at present.
First, a “cool toy”
At this site there is a very cool animation of the nearby stars. It shows those stars with a square grid reference plane, a pointer to the galactic core, and it rotates the plane so you can see the perspective of the position of those stars in a 3-D kind of way. Hover your cursor over a star, and the data for that star is displayed. I found it very helpful for visualizing just where Bernard’s Star and Alpha Centauri were located, along with Sirius.
It’s just a neat tool / toy.
So, for example, near the most empty corner of the grid, there are two stars very close to each other. Hovering of them I found them to by Luyten’s Star and Procyon. These two are within 1.1 light years of each other. This matters as that means they are likely to be gravitationally acting on each other. It also lets you see how close 1.1 light years really is (and realize that in a hundred thousand years we’ll have a star that close to us…). Procyon is itself a binary system with one star about 1.5 sol masses and the other about half a solar mass. So is Luyten’s star part of a trinary system? Will it become gravitationally bound?
Elsewhere on the graph you find Bernard’s star. It’s a red dot a bit above the reference plane, near the center of the outer edge, when Alpha Centauri is on the left of Sol (it’s the distinct binary that is below the plane and nearest the sun). Bernard’s star is very old at 7 to 12 billion years and is class M. It is a low mass red dwarf ( about 0.15 sol) and is headed our way “right quick”. It will be our closest neighbor in 11,700 AD at 3.8 light years. So, will we capture it? Or are we already orbiting each other? (Or are we mutually orbiting some other thing).
Well, that all depends on something called the “Hill Sphere”
An astronomical body’s Hill sphere is the region in which it dominates the attraction of satellites. For a planet to retain a moon, the moon must have an orbit that lies within the Hill sphere of the planet. That moon would, in turn, have a Hill sphere of its own. Any object within that distance would tend to become a satellite of the moon, rather than of the planet itself.
In more precise terms, the Hill sphere approximates the gravitational sphere of influence of a smaller body in the face of perturbations from a more massive body. It was defined by the American astronomer George William Hill, based upon the work of the French astronomer Édouard Roche. For this reason, it is also known as the Roche sphere (not to be confused with the Roche Limit). The Hill sphere extends between the Lagrangian points L1 and L2, which lie along the line of centers of the two bodies. The region of influence of the second body is shortest in that direction, and so it acts as the limiting factor for the size of the Hill sphere. Beyond that distance, a third object in orbit around the second (e.g. Jupiter) would spend at least part of its orbit outside the Hill sphere, and would be progressively perturbed by the tidal forces of the central body (e.g. the Sun), eventually ending up orbiting the latter.
So “keep your friends close” or they end up wandering off to the bigger party…
The math is pretty clear (from the wiki):
If the mass of the smaller body (e.g. Earth) is m, and it orbits a heavier body (e.g. Sun) of mass M with a semi-major axis a and an eccentricity of e, then the radius r of the Hill sphere for the smaller body (e.g. Earth) is, approximately
When eccentricity is negligible (the most favourable case for orbital stability), this becomes
In the Earth example, the Earth (5.97×1024 kg) orbits the Sun (1.99×1030 kg) at a distance of 149.6 million km. The Hill sphere for Earth thus extends out to about 1.5 million km (0.01 AU). The Moon’s orbit, at a distance of 0.384 million km from Earth, is comfortably within the gravitational sphere of influence of Earth and it is therefore not at risk of being pulled into an independent orbit around the Sun. All stable satellites of the Earth (those within the Earth’s Hill sphere) must have an orbital period shorter than 7 months.
OK, so if we know the masses and how close things come we can figure out who will steal what objects from whom.
But are we already “gravitationally bound” to those other stars? We are all gravitationally bound into the Milky Way, but what about this bunch near us, anything special?
Open clusters are also called galactic clusters. They usually contain somewhere between a dozen and a thousand stars. They are held together by mutual gravitational attraction and have a common center of mass. Open star clusters are composed of hot, relatively young stars and tend to be found within the spiral arms of our Milky Way galaxy. It is estimated that there are about 20,000 open star clusters in our galaxy. The reason open clusters are so young is because they don’t last very long. Gravitational interactions between the stars and other objects will cause these clusters to eventually disperse over time. Open clusters are formed when several stars are formed at the same time from the same cloud of dust and gas. Our own Sun is part of an open cluster than includes other nearby stars such as Alpha Centauri and Barnard’s star. All of these stars are believed to have formed from the same primordial nebula around 5 billion years ago. We know that the stars in open clusters are young because their spectrums indicate that an abundance of heavy elements. These elements are formed through many generations of star birth and death. Over billions of years, this stellar cycle produces star-forming clouds rich in heavy elements. Open clusters are formed from clouds like these.
Says we’re all one group, but will eventually start to fling some guys out of the club.
That implies we are all orbiting our local center of mass, but in an unstable way as we approach each other and cause orbits to shift. We’ve not settled into a rotating disk with orbital resonances worked out. Probably because the mass of the Milky Way puts us inside it’s Hill Sphere and outside of each others.
So when Bernard’s Star comes “whizzing by” in just about 9,000 years, it will keep on going. At least for a while. In the process, we will end up shifting our position in the group a bit too.
In this link there is a list of nearby stars and how close they will eventually come to us:
The surprise to me is Gliese 710 that ends up 1.01 light years from us in 1,447,000 years. Depending on how fast it is going then and how heavy it is, that’s close enough to start forming binary systems. Unfortunately, it’s only about 1/2 a solar mass and moving really fast, so the odds of us capturing it are near zero. (Though the exact closeness of approach is not known so things are a bit ill defined…)
From the Gliese 710 wiki
More recent calculations by Bobylev in 2010 suggest Gliese 710 has an 86 percent chance of passing through the Oort cloud, considering the Oort cloud to be a spheroid around the Sun with semiminor and semimajor axes of 80,000 and 100,000 astronomical units. The distance of closest approach of Gliese 710 is difficult to compute precisely as it depends sensitively on its current position and velocity; Bobylev estimates that it will pass within 0.311 ± 0.167 pc (1.01 ± 0.54 light years) of the Sun. There is even a 1/10,000 chance of the star penetrating into the region (d < 1,000 AU) where the influence of the passing star on Kuiper Belt objects is significant.
The star with the second greatest perturbational effect in the past or future 10 million years was Algol, a triple star system that passed no closer than 9.8 light years, 7.3 million years ago, but with a considerably larger total mass of 5.8 solar masses, which is mirrored in the star being known as the Demon Star and traditionally being considered the unluckiest star in the sky.
OK, so at 7.3 million years ago we had something come very close as well. (Further back in time it becomes ever harder to figure the orbits and passages that might have happened, so far far back in time, like a billion years, and all bets are off).
But that “hitting the Oort cloud” bit doesn’t sound like such a good idea. Isn’t that where they keep telling us all the comets that are going to pulverize the planet come from?
Ok, well, in a million years we can start worrying about it…
But one thing is clear: The stars are not nearly so “fixed in the heavens” as we like to think. It’s more like a pinball machine out there. Even on the stellar scale.
I’ve just got to think that a star passing through that mess has got to be an issue for us… And that it’s +/- 1/2 a light year is, er, something to think about.
As for Alpha Centauri, that wiki says:
Based on these observed proper motions and radial velocities, Alpha Centauri will continue to slowly brighten, passing just north of the Southern Cross or Crux, before moving northwest and up towards the celestial equator and away from the galactic plane. By about 29,700 AD, in the present-day constellation of Hydra, Alpha Centauri will be 1.00 pc or 3.26 ly away. Then it will reach the stationary radial velocity (RVel) of 0.0 km/s and the maximum apparent magnitude of −0.86V — similar to present day Canopus. Soon after this close approach, the system will begin to move away from us, showing a positive radial velocity.
Due to visual perspective, about 100,000 years from now, these stars will reach a final vanishing point and slowly disappear among the countless stars of the Milky Way. Here this once bright yellow star will fall below naked-eye visibility somewhere in the faint present day southern constellation of Telescopium. This unusual location results from Alpha Centauri’s orbit around the galactic centre being highly tilted with respect to the plane of our Milky Way galaxy.
So about the time we are exiting from the next Ice Age Glacial, Alpha Centauri will be fading for our local group.
OK, this all leads me to think that the other, more distant, stars in our local group are also unlikely to join us as a binary system either, before our little cluster breaks up and spreads out. None of them are very big, nor do they get any closer than these guys.
So while something might have wandered by in the past, and we could still have some Oort Cloud Action in the future, there isn’t a whole lot after that in our future (and probably not much in the recent past either).
There have been a bunch of folks who have, from time to time, thought we needed an outside influence to account for some orbital aspect or another. This hypothetical companion is often called “Planet X”.
Think they can limit the range of “possibles”.
If Planet X was out there, where would it be? This question posed by an Italian researcher turns out to be a lot more involved than you’d think. [...] By analysing the orbital precession of all the inner-Solar System planets, the researcher has been able to constrain the minimum distance a hypothetical object, from the mass of Mars to the mass of the Sun, could be located in the Solar System.
They note that the proposed “other star” is named “Nemesis”.
The name “Planet X” was actually coined by Percival Lowell at the start of the 20th century when he predicted there might be a massive planet beyond the orbit of Neptune. Then, in 1930, Clyde Tombaugh appeared to confirm Lowell’s theory; a planet had been discovered and it was promptly named Pluto. However, as time went on, it slowly became apparent that Pluto wasn’t massive enough to explain the original observations of the perturbations of Uranus’ orbit (the reason for Lowell’s Planet X prediction in the first place). By the 1970′s and 80′s modern observation techniques proved that the original perturbations in Uranus’ orbit were measurement error and not being caused by a massive planetary body.
To cut a long story short, if a massive planetary body or a small binary sibling of the Sun were close to us, we would notice their gravitational influence in the orbital dynamics of the planets. There may be some indirect indications that a small planetary body might be shaping the Kuiper Cliff, and that a binary partner of the Sun might be disturbing the Oort Cloud every 25 million years or so (relating to the cyclical mass extinctions in Earth’s history, possibly caused by comet impacts), but hard astronomical proof has yet to be found.
And at this point I have to note that the 25 million year interval is way longer than all those “nearby” stars are taking to come flying past. So Nemisis would have to be a lot further away (and so unlikely to be gravitationally bound to us), or moving very slowly and nearby (but dark and small). Also a bit on the unlikely side. (Though not impossible. There could be some kind of small dark object out there, but the energetics are just not looking good). If it were a “brown dwarf” we ought to see it on infrared. While it’s possible we’ve not seen it, that’s a hard sell. If it is a tiny black hole, it must be blessed with no nearby matter to feed on or we would see the accretion disk glowing. If it’s larger than a very dark brown dwarf, it ought to be visible in the visible range like all the other nearby stars we’ve spotted.
The only way I can make this work out easily is that it WAS in the area, but left after that last 25 MYa visit much as Gliese 710 is going to do in about 1.5 MY. That is a reasonable scenario.
It turns out that all the planets the mass of Mars and above have been discovered within the Solar System. Iorio computes that the minimum possible distances at which a Mars-mass, Earth-mass, Jupiter-mass and Sun-mass object can orbit around the Sun are 62 AU, 430 AU, 886 AU and 8995 AU respectively. To put this into perspective, Pluto orbits the Sun at an average distance of 39 AU.
That 8995 AU distance is about 0.14 light years. I think we would have noticed another star at that range. The article goes on to assert that we would have seen a planet like object at those kinds of ranges:
So if we used our imaginations a bit, we could say that a sufficiently sized Planet X could be patrolling a snail-paced orbit somewhere beyond Pluto. But there’s an additional problem for Planet X conspiracy theorists. If there was any object of sufficient size (and by “sufficient” I mean Pluto-mass, I’m being generous), according to a 2004 publication by David Jewitt, from the Institute for Astronomy, University of Hawaii, we would have observed such an object by now if it orbited within 320 AU from the Sun.
[...]Sorry, between here and a few hundred AU away, it’s just us, the known planets and a load of asteroids (and perhaps the odd plutino) for company.
The idea that precession was caused not by the earth changing orientation, but by a companion is a rather old one.
It dates back to an Indian astronomer in 1894:
The Holy Science
Main article: The Holy Science
Sri Yukteswar wrote The Holy Science in 1894. In the introduction, he wrote:
“The purpose of this book is to show as clearly as possible that there is an essential unity in all religions; that there is no difference in the truths inculcated by the various faiths; that there is but one method by which the world, both external and internal, has evolved; and that there is but one Goal admitted by all scriptures.”
He was also “way into religion”…
The work introduced many ideas that were revolutionary for the time — for instance Sri Yukteswar broke from Hindu tradition in stating that the earth is not in the age of Kali Yuga, but has advanced to Dwapara Yuga. His proof was based on a new perspective of the precession of the equinoxes. He also introduced the idea that the sun takes a ‘star for its dual’, and revolves around it in a period of 24,000 years, which accounts for the precession of the equinox. Research into this theory is being conducted by the Binary Research Institute, which produced a documentary on the topic titled The Great Year, narrated by James Earl Jones. A sign of the ubiquity of Sri Yukteswar’s calculations in modern culture is that there is an iPhone Application for calculating them, just as there are calculators for currencies, lengths, areas and volumes
The theory of the Sun’s binary companion expounded by Sri Yukteswar in The Holy Science has attracted the attention of David Frawley, who has written about it in several of his books. According to Frawley, the theory offers a better estimate of the age of Rama and Krishna and other important historical Indian figures than other dating methods, which estimate some of these figures to have lived millions of years ago — belying accepted human history.
OK, so those “Binary Research Institute” folks, what’s there take on things?
Well, they do make a couple of good points, but mostly of the form “We have some issues with precession and some present orbits that are neatly explained by a hypothetical binary companion”. All well and good, but were are the observations of that star? ( I know, “absence of evidence is not evidence of absence”… but still, we’re talking about a star in our neighborhood here…)
Since launching the Binary Research Institute website a few years ago, we have continued to research the possibility that our Sun might be part of a binary or multiple star system. This includes investigating a number of issues related to the Sun’s motion, and the methodology of finding other celestial objects. To that end:
• In late 2002 we traveled to the outback of Australia to view a total eclipse of the Sun and discussed the Sun’s motion and related topics with Tom Van Flandern, former head of U.S. Naval Observatory. Conclusion: eclipse cycles indicate the earth moves 360 degrees around the sun in a tropical year, inconsistent with current lunisolar precession theory.
• In mid 2003 we went to the Big Island of Hawaii and The Keck Observatory and spent a good bit of the night with Geoff Marcy, Professor of Astronomy at UC Berkley, as he searched for extra-solar planets (he and his team have found more than 100 so far!). Conclusion: we know less than 1% of the universe and it is likely there will be a number of discoveries over the next few decades that require us to remodel local space.
• We have also met personally, or most often through conferences and the Internet, with a number of astrophysicists and astronomers around the world and discussed the topic of precession and its nuances. Conclusion: precession mechanics is one of the least understood topics in science today!
• The 26th Annual IAU General Assembly determined:
1. the need for a precession theory consistent with dynamical theory,
2. that, while the precession portion of the IAU 2000A precession-nutation model, recommended for use beginning on 1 January 2003 by resolution B1.6 of the XXIVth IAU General Assembly, is based on improved precession rates with respect to the IAU 1976 precession, it is not consistent with dynamical theory, and
3. that resolution B1.6 of the XXIVth General Assembly also encourages the development of new expressions for precession consistent with the IAU 2000A precession-nutation model.
The only way we have found to solve the IAU’s concern, is to replace the precession part of the precession-nutation model with a precession theory based on a moving solar system (the binary model). Such a model is consistent with dynamical theory, as it allows local dynamics to determine short period motions such as nutation, and it provides a more accurate way to predict changes in the rate of precession without the complexity of the 2000A precession-nutation model.
All of which is nice and all, and indicates they hang out with the professional astronomer crowd. But it’s still a thesis looking for evidence.
The best short from description of why folks would take this view was found in a comment here:
Hi Mike – Sedna’s periodicity is in 2:1 resonance with the orbit of the companion star hypothesized by the Indian astronomer Sri Yukteswar in 1894. Yukteswar suggested that our sun’s motion around the common center of mass was the primary cause of the observable we call precession (in contrast to the lunisolar theory of precession that requires a static solar system). I plugged his numbers into a model and found it to be highly accurate in predicting changes in the precession rate. In fact, if you compare Yukteswar’s 1894 moving solar system model of precession with Newcomb’s 1897 precession equation, the binary model was 41 times more accurate over the next 100 years (based on P rate in Astronomical Almanac of 1900 and 2000). This implies that the bulk of the observable of the stars moving retrograde across the sky at about 50”p/y is actually due to motion of the solar system frame relative to the VLBI reference points, and very little due to local gravitational forces tugging on the oblate earth (although that local dynamic does cause nutation). Of course no companion star has yet been found but it shows your speculative ideas concerning a rogue star might not be so rogue after all. Incidentally, it may also solve the IAU’s problem that the precession equation is “not consistent with dynamical theory”. Keep up the good work!
That page also includes some insight into why folks would postulate a nearby star that we’re not seeing.
Seven years ago, the moment I first calculated the odd orbit of Sedna and realized it never came anywhere close to any of the planets, it instantly became clear that we astronomers had been missing something all along. Either something large once passed through the outer parts of our solar system and is now long gone, or something large still lurks in a distant corner out there and we haven’t found it yet.
Our first idea was that perhaps there was an unknown approximately earth-sized planet circling the sun about twice the distance of Neptune. Sedna could have gotten too close to this Planet X and been given a kick which would have flung it out into a far corner of our solar system
The second possibility that we considered and wrote about was that perhaps a star had passed extremely close to our solar system at some point during the lifetime of the sun. “Extremely close” for a star means something like 20 times beyond the orbit of Neptune, but that is 500 times closer than the current nearest star. A star passing by that close would have been brighter than the full moon and would have been the brightest thing in the night sky for hundreds of years. Perhaps our early ancestors even temporarily lived under a dual-star sky. Sedna, before the rogue star came calling,
They have a nifty picture at this point with two suns seen from earth.
The third possibility was the one that we deemed the most likely. Instead of getting one big kick from an improbably passing star, imagine that Sedna got a lot of really small kicks from many stars passing by not quite as closely. The chances of this happening might seem low, too, but astronomers have long known that most stars are born not alone, but in a litter of many stars packed together
As we have evidence for a close approach of a known star “soon” in geologic time scales (and, in theory, we’d have had more close approaches in the past when there were more stars nearby; and given an expanding universe, everything was nearer by) I’m not seeing the need to postulate a present invisible partner to explain a past event for which the present objects are sufficient. We’ve had on the order of billions of years for such an event, and we’re seeing one likely in the next 100,000 years. Plenty of scale there for many to have happened in the last couple of billion years.
For what it is worth, these folks give a good explanation / example of why folks find the thesis attractive. It lets them have a better and easier prediction of precession:
I’m not going to quote any of it here as I think it really needs to be seen as a whole to have effect.
The one “niggling bit” that bothers me is their assertion that we use a non-precession set of coordinates for professional astronomers to find things inside the solar system, but a precessional one for things outside the solar system. I have no way to verify the veracity of that statement.
To the extent it is true, that objects inside the solar system do not show the 24,000 year precessional cycle, then it simply must be that the solar system as a whole is rotating and / or orbiting something. But what?
My candidate would simply be the center of mass of the local star cluster. There doesn’t need to be a physical object, just the net of all local gravitational vectors. Unfortunately, trying to solve an n-body problem with an unknown number of bodies is simply impossible. A decent shot at it could be done if our local group of stars is significantly isolated from all the other groups for a few dozen light years around, but even that would take data, software, and computer time that I simply don’t have. Inspection of that image of local stars, and looking at their relative motions, does not look real promising either. Other stars ought to be orbiting that barycenter too, yet they are going to leave the area (for Alpha Centauri) and go whizzing by for Bernard’s star. Unless our period of collected data is just too short to resolve the actual motions, I’m not seeing this as a stong case.
Then again, our understanding of the rate of the precession of the equinoxes is limited to about 10,000 years of human history. That isn’t even one full cycle (of 24,000 years). So perhaps the answer is simply that it’s easy to see a 24,000 year “periodic function” that isn’t really there. That the actual function is some more “open” process that only looks cyclical when viewed in a very short time frame. A Hundred Million years is a very long time… Could the whole solar system simply be in a ‘flat spin’ of 24000 years from some prior event long ago? I just don’t know.
But I’m not seeing the compelling case for an invisible companion star at this point. I’d find it easier to believe that the whole solar system has net angular momentum distinct from the orbits of the planets about the sun, and we are interpreting that as “precession of the pole” when it isn’t. Perhaps there is some way to disambiguate that case, but I’m just not seeing it at 2 AM… Further, given how things are moving now, we have lots of opportunities for things in the distant past to have stirred the pot and then left the neighborhood.