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Fraser
2006-Jul-19, 04:07 AM
If you want to send an interstellar probe, you're going to chose the closest star. And that would be Proxima Centauri, located only 4.2 light years away. Since they first calculated its distance, astronomers have always assumed that Proxima Centauri was part of the Alpha Centauri triple star system. But recent calculations threw that assumption into doubt. Was its location purely a coincidence? Is Proxima Centauri flying solo through the Milky Way?

Read the full blog entry (http://www.universetoday.com/2006/07/18/is-proxima-centauri-flying-solo/)

rocketblair
2006-Jul-19, 06:52 AM
In reading the blog, it doesn't appear that proxima's association with the centauri system is being questioned THAT much, but it will be interesting to see future calculations done to show it's movement in relation to the two larger suns in the system. The idea that stable planets might exist there is something I had not considered plausible, perhaps the planet hunters will give the centauri system a closer look as their ablilty to find smaller worlds improves.

tony873004
2006-Jul-19, 08:29 AM
13,000 AU seems way too far for it to have orbited for billions of years without being stripped away. But of course, Sol has Oort cloud members orbiting it at greater distances. And Sol is less massive than the combined Alpha Centauri AB.

But 13,000 is way too close for a non-bound star to be from the AB members, unless high odds are being defied. It wouldn't surprise me too much if we found some random star system in our galaxy that broke these odds. But for it to be our next-door neigbor is remarkable.

This is an interesting one. Is it bound? On one hand, it can't be, because the odds are against it being bound. On the other hand, it has to be because the odds are against it not being bound.

It's possible that it is a captured object (my guess). A double star system is much more efficient at capturing objects from interstellar space than a solo star like the Sun. And such a captured object should be in a loosely-bound, highly-eccentric orbit with a large semi-major axis, just like.... hmmm...

Such a captured object is likely to stick around for a few tens to hundreds of million years (my guess). This might yield a clue as to the population of red dwarfs in the galaxy. The more numerous they are, the more likely that binary stars will capture them. And the fact that our closest neighbor captured one implies that they are numerous.

tony873004
2006-Jul-19, 08:51 AM
The linked paper almost certainly has a typo in the data:

For the case of a highly eccentric Keplerian orbit, Proxima Centauri would spend most of its time near apastron. The current distance of Proxima Centauri from Alpha Cen A/B is 15000 +/- 700 AU, thus the estimated semi-major axis of 272212 AU is almost certainly far too large.
How would an object at an apastron of 15000 AU have a semi-major axis of 272212 AU? 15000 AU would be more like a periastron of an orbit with a semi-major axis of 272212 AU. Furthermore, 272212 AU is 4.3 light years. That is WAY outside Alpha Cen A/B's Hill Sphere. And coincidentally, that's Proxima Centauri's distance from the Sun.

antoniseb
2006-Jul-19, 11:49 AM
This is a pretty cool story. As to whether Proxima was captured or part of the original system, (this can be proved wrong if the age of Proxima can be found to be substantially different from Alpha Centauri A&B) I expect that it was probably formed from the same cloud at roughly the same time. I don't know whether it is a Giant Jupiter that was kicked out during the inward migration of "B", or whether it was a loose interloper captured in a chance interaction with A&B while the new star cluster was still very dense.

Romanus
2006-Jul-19, 02:21 PM
There's a minor typo in the article--Beta Centauri should probably be Alpha Centauri B. Proxima orbits the Alpha Centauri AB system. Beta Centauri is Hadar, a much more distant star.

Fraser
2006-Jul-19, 04:11 PM
Okay, I've fixed that. Thanks!

trinitree88
2006-Jul-20, 12:10 AM
This is a pretty cool story. As to whether Proxima was captured or part of the original system, (this can be proved wrong if the age of Proxima can be found to be substantially different from Alpha Centauri A&B) I expect that it was probably formed from the same cloud at roughly the same time. I don't know whether it is a Giant Jupiter that was kicked out during the inward migration of "B", or whether it was a loose interloper captured in a chance interaction with A&B while the new star cluster was still very dense.

Antoniseb. I believe I read many moons ago, that stars that form from the same primordial dust cloud have matching magnetic polarity....so if the "intruder" has a different magnetic orientation, in addition to it's age as indicated, being different...that's two clues.Though in fairness, the regular polarity shift of the sun is likely attributable to it's largest satellite...jupiter. (Steve Strom, UMass, Amherst...magnetic polarization of stars in clusters). :shifty: Pete

Blob
2006-Jul-20, 12:39 AM
Alpha Centauri B is an orange star, a little cooler and a little less massive than the Sun. Alpha Centauri A and B orbit each other at a distance of about 3.6 billion kilometres.

http://static.flickr.com/41/76212124_c5b51d94ff_o.gif

* Parallax: 0.742 arcsecs
* Spectral type: K0-1 V
* Radial velocity: -21 km/s
* Proper Motion: 3.724 arcsecs/year
* Apparent Visual Magnitude: 1.35
* Absolute Visual Magnitude: 5.70
* Luminosity: 0.5 Solar Luminosities
* Diameter: 0.865 times that of the Sun
* Angular diameter: 6.002 milliarcseconds

qraal
2006-Jul-20, 11:12 AM
Hi All

Proxima may or may not be bound. The difference in velocities between the two possibilities is hidden in the error bounds of current measurements, so only tighter data will answer the question.

Adam

Jerry
2006-Jul-20, 01:34 PM
The linked paper almost certainly has a typo in the data:

How would an object at an apastron of 15000 AU have a semi-major axis of 272212 AU? 15000 AU would be more like a periastron of an orbit with a semi-major axis of 272212 AU. Furthermore, 272212 AU is 4.3 light years. That is WAY outside Alpha Cen A/B's Hill Sphere. And coincidentally, that's Proxima Centauri's distance from the Sun.
...Maybe it is in orbit about the sun.

Nice catch, Tony, and why not launch a probe to the alpha system? Deep space probes like pioneer and voyager have proven remarkably resilient, and there is much to learn along the way. Shuttle's final days should be spent hauling and assembling space boosters, not taking food and bandages to the ISS and hauling away garbage. Lets just do it.

antoniseb
2006-Jul-20, 02:52 PM
why not launch a probe to the alpha system? Deep space probes like pioneer and voyager have proven remarkably resilient, and there is much to learn along the way.

One reason is that even if we did launch such a probe we don't have any technology that could provide it with enough energy to transmit signals to us for more than a few hundred years. With our best rockets today, that would mean we'd lose touch before it had completed one percent of the journey.

I'm not saying we can never get there. I'm just saying that we can't do it now as an alternative to supplying the ISS.

TorontoAstro101
2006-Nov-20, 04:45 AM
hey guys,

my first post on the forum. sweet.

i was just wondering, would any of you happen to know the semi-major axes of the following stars: Alpha Centauri A & B, Proxima, and Sirius A & B? Google wasn't much help, and i need these answers ASAP!

thanks for the help.

TorontoAstro101

antoniseb
2006-Nov-20, 12:51 PM
Google wasn't much help
Google wasn't much help? Try Wikipedia then.