One of the things we need to learn about the Alpha Centauri stars is whether Proxima Centauri is gravitationally bound to Centauri A and B. Much hinges on the issue, for if Proxima is merely passing in the night, then whatever disruptive effect it may have upon an outer halo of comets around the Centauri stars would be a one-shot affair. On the other hand, if Proxima is a stable part of this system, then it may send comets laden with volatiles into whatever planetary systems are around Centauri A and B. Proxima might be, in other words, the difference between dry rocky worlds and planets with abundant water, with all that implies about the possibilities for life.
We’ve seen the same kind of thinking applied to our own Solar System in the form of the star dubbed ‘Nemesis.’ As the theory goes, Nemesis could be a red or perhaps a brown dwarf that could account for what seems to be a periodicity in terms of extinction events on Earth. Disrupting cometary orbits in the Oort Cloud, such an object might send comets into the inner system on a 26-million year cycle. The Telegraph is one of a variety of media looking into the story (Astrobiology Magazine is another), and speculating on whether or not some evidence for Nemesis has turned up in the orbit of Sedna, the dwarf planet discovered in 2003 whose orbit continues to cause ripples in the planetary sciences community.
The Telegraph quotes the object’s discoverer, Mike Brown (Caltech), on the matter:
“Sedna is a very odd object – it shouldn’t be there! It never comes anywhere close to any of the giant planets or the sun. It’s way, way out there on this incredibly eccentric orbit. The only way to get on an eccentric orbit is to have some giant body kick you – so what is out there?”
Did someone say ‘eccentric’? Sedna gives new meaning to the term, with a perihelion of 76 AU and an aphelion of a whopping 975 AU, making for an orbital period lasting as long as 12,000 years. Brown himself says his own surveys would not have picked up anything as distant and slow-moving as Nemesis would have to be, all of which leaves the prospects for an unseen companion still very much alive.
In a 2006 paper, Rodney Gomes (Observatório Nacional, Brazil) and colleagues note that Sedna and the object 2000 CR105 stand out from the thousand or so trans-Neptunian objects thus far discovered because their trajectories cannot be accounted for by the planetary configuration we know about. The authors call them ‘the first discovered true inner Oort cloud objects.’ They may be evidence of a distant planetary-mass solar companion, one the authors characterize as follows:
A small mass companion (roughly Earth to Neptune mass) could have formed within the planetary region, been ejected to its current heliocentric distance by gravitational scatterings of Jupiter and Saturn. Such a body may have been ejected from the Solar System after producing the DDP [distant detached population], or it could remain as the largest member of the standard scattered disk population. Or its perihelion could have been raised by perturbations of passing stars which would have needed to have been passing at a closer distance than would be reasonable to hypothesize subsequent to the dispersal of the Sun’s birth cloud/cluster, but not as close as required for direct stellar perturbations producing the observed high perihelion scattered disk objects. A Jupiter mass or larger object on a highly inclined orbit beyond 5000 AU would most likely have formed as a small, distant binary-star like companion, e.g., by fragmentation during collapse or capture.
With WISE (Wide-Field Infrared Explorer) on the case, it may not be too long before we have evidence one way or the other. Chances are a red dwarf no more than 25,000 AU out would have been spotted by now, but a brown dwarf might still elude detection. John Matese (University of Louisiana at Lafayette), one of the authors of the above paper, has been studying Nemesis possibilities for more than two decades, and now opts for an object about three to five times the size of Jupiter as a possible cause of the cometary commotion. WISE will need until perhaps mid-2013 before two sky scans and telescopic follow-ups of any Nemesis-like detection can be completed.
For more, see Gomes et al., “A Distant Planetary Mass Solar Companion May Have Produced Distant Detached Objects,” Icarus 184, No. 2 (October, 2006), where the authors say the object in question could be an Earth-mass planet at 1000 AU, a Neptune-mass planet at 2000 AU, or a Jupiter-mass object at 5000 AU or farther (abstract). So maybe we’re not talking about a ‘death star’ at all, but a huge Planet X of the kind Percival Lowell was once so intent on finding. Lowell, thanks to the indefatigable Clyde Tombaugh, had to settle for tiny Pluto, but we’ve yet to rule out much larger objects in the dark realms beyond the Kuiper Belt. WISE should settle the matter conclusively in about three years.
At Oort cloud distances, orbital velocity would be very low, and it would not take much to severely disturb an object’s orbit. How has it been excluded that a simple close approach or collision between two objects of Sedna’s size could send one of them into the inner system? If it has not, is there really a need for sinister speculation about unseen large planets?
“…if Proxima is merely passing in the night, … On the other hand, if Proxima is a stable part of this system…”
3rd possibility: Proxima and Alpha AB have been corralled together by the spiral gravitational potential of the Galaxy…
( See: http://rqgravity.net/images/spiralmotions/funnel2.gif )
…which might make them traveling companions of many, many millions of years, but destined for an eventual breakup once the system reaches the apsis of perigalacticon.
Interesting as those possibilities are, what if there’s something more exotic like a “mirror matter” star? That’d be a transformational discovery.
“(…) whether Proxima Centauri is gravitationally bound to Centauri A and B. (…) if Proxima is merely passing in the night, (…). On the other hand, if Proxima is a stable part of this system
Whichever is the case, passing or stable part, it seems unlikely that they originated together.
Proxima may have been captured by the gravity Alpha AB to become a very rare example of a secondary (or non-original, non-indigenous) multiple star system.
By far most binaries/multiples have originated together from the same primordial gas cloud.
However, it seems very unlikely that with such an enormous distance (about 0.2 ly or 12000 AU) separating Proxima and Alpha AB, that they originated together.
The same is the case for Zeta 1 and 2 Reticuli (0.1 ly or 6000 AU).
Unless there exists a star formation process after which two components separate this far in a later stage.
“[I]t seems very unlikely that with such an enormous distance (about 0.2 ly or 12000 AU) separating Proxima and Alpha AB, that they originated together. The same is the case for Zeta 1 and 2 Reticuli (0.1 ly or 6000 AU).”
I don’t think the distance factors into the likelihood.
Zeta Reticulli is a pair of G dwarfs — so the ages can be checked against (admittedly rough) astrophysical models to see if they vaguely correspond (that’s not possible to assess the age of Proxima Cen. — an M dwarf.)
Epsilon 1 & 2 Lyrae (the “double double” star) is another example of a pair widely separated to this scale — the component stars have earlier spectral types (A & F), so they are more massive and hence assuredly young stars which, circumstantially, must be ‘coeval’ (born together).
Cheers,
…. a brown dwarf is an interesting concept, to find a very “cool” star orbiting our own has other implications like say a “nano-planet” within its habitable zone that might have recieved some of the same organic materials that our solar system did in its infancy……
….now that might jumpstart some of our politicians into giving the green light to a more robust space program!……..
Here’s a wild thought. What if the “dark mass” lurking out there, trimming the Kuiper Belt and perturbing the Oort, is a gravitational accelerator, just like Bob Forward speculated Pluto might’ve been back in the early 1960s? He collected that article in a later book, but originally wrote it for “Analog” under a pseudonym. Black-holes, if there are higher dimensions, can form just the kind of “rolling torus” that can act as a gravitational accelerator. Forward suggested it might precess and thus cover a large part of the sky, thus allowing us to fire off starships to multiple destinations and join the Galactic community.
Tyche and Nemesis may be hiding in plain sight in the dwarf flare star Proxima Centauri (Proxima) orbiting the sun at 270,000 AU, but presently deflected into a hyperbolic trajectory around the passing star Alpha Centauri AB. Anosova et al., 1994, calculated that Proxima is in an (unbound) hyperbolic orbit around Alpha Centauri AB “with the probability of P = 1.0”.
Proxima lies directly on the orbital plane, with galactic coordinates: L = 313.9400 B = -1.9273, of the predicted perturbator, Tyche, of the long-period Oort cloud comets (hillscloud.wordpress.com) as calculated by Matese, Whitman and Whitmire. (Matese, 1999) also (Matese & Whitmire, 2011)
Proxima also has the distance and mass to be Nemesis and perhaps the highly-eccentric orbital trajectory from repeated close encounters with passing stars like Alpha Centauri.