What Do Orbital Motions of Outer Planets Reveal About the Pioneer Anomaly?

[varsha]

http://spaceflightnow.com/news/n0601/09milkyway/ http://spaceflightnow.com/news/n0601/11hubbleorion/

 

[SpaceTiger]

Also, check this out:

http://www.astronomy.com/asy/default.aspx?c=a&id=3841"

It's an announcement from one of the groups I'm working with. We've found an overdensity of stars in the SDSS survey that, if real, might represent the nearest galaxy to the earth. My roommate is the first author on the paper (Juric et al.).

 

[Garth]

Thank you ST - if real, then a low mass galaxy of ~ 10⁶ stars and about 20,000 light yrs across? (Subtends ~30⁰ at 30,000 lgt yrs.) So a very low stellar density galaxy.

Would it be noticed if further away, and if not then how many more are there out there?

Garth

 

[varsha]

Also, check this out:
http://www.astronomy.com/asy/default.aspx?c=a&id=3841"
It's an announcement from one of the groups I'm working with. We've found an overdensity of stars in the SDSS survey that, if real, might represent the nearest galaxy to the earth. My roommate is the first author on the paper (Juric et al.).

pity i can't subscribe to this. do you know any other stuff that i can subscribe to freely, via e-mail?

 

[SpaceTiger]

Would it be noticed if further away, and if not then how many more are there out there?

I don't think it would have been, mainly because a galaxy as sparse as this would have an extremely low surface brightness. Your second question is so far unanswered, but LCDM theorists are trying hard to. An abundance of such galaxies would lead to a possible resolution of the "small-scale structure problem". This arises from the fact that the standard model seems to overpredict the number of small dark matter halos in the vicinity of the Milky Way. If they were present but escaping detection, then there would no longer be a discrepancy.

 

[SpaceTiger]

pity i can't subscribe to this. do you know any other stuff that i can subscribe to freely, via e-mail?

I'm not subscribed either. Are you saying you can't see the article?

 

[Garth]

I don't think it would have been, mainly because a galaxy as sparse as this would have an extremely low surface brightness. Your second question is so far unanswered, but LCDM theorists are trying hard to. An abundance of such galaxies would lead to a possible resolution of the "small-scale structure problem". This arises from the fact that the standard model seems to overpredict the number of small dark matter halos in the vicinity of the Milky Way. If they were present but escaping detection, then there would no longer be a discrepancy.

Yes, that was my drift. About ten years ago I heard a presentation of a paper that suggested the inter-cluster voids may in fact be not as deficient in density as they appear but filled with very low surface brightness galaxies that cannot be observed.

Garth

 

[SpaceTiger]

Yes, that was my drift. About ten years ago I heard a presentation of a paper that suggested the inter-cluster voids may in fact be not as deficient in density as they appear but filled with very low surface brightness galaxies that cannot be observed.

I'm sure that's possible as well. That wasn't work by Michael Vogeley, was it? I know he's big into the voids.

Fortunately for LCDM, the problems seem to lie in the regimes in which we have the least observational and theoretical certainty. If, instead of "small-scale structure" and "cuspiness" problems, we had "large-scale structure" and "rotation curve" problems, LCDM would be in a lot of trouble.

 

[varsha]

I'm not subscribed either. Are you saying you can't see the article?

well i can... but it's a magazine isen't it? so it's not free. and i can't get it through e-mail.

 

[SpaceTiger]

well i can... but it's a magazine isen't it? so it's not free. and i can't get it through e-mail.

I don't really know, I was just linking the story. I don't subscribe to any pop. sci. magazines or email services, so hopefully someone else can offer some suggestions.

 

[Nereid]

I have no trouble accessing it.

However, you could always go to the official SDSS website (well, one of them), and you'd find a link to a story on this very topic: http://www.sdss.org/news/releases/20060109.virgooverdensity.html". From my quick skim of both, I'd say the SDSS one is the better.

 

[Garth]

I have no trouble accessing it.
However, you could always go to the official SDSS website (well, one of them), and you'd find a link to a story on this very topic: http://www.sdss.org/news/releases/20060109.virgooverdensity.html". From my quick skim of both, I'd say the SDSS one is the better.

And that story refers to our very own SpaceTiger. Well done ST!
So what is the limit on DM is there in our neighbourhood? And does this go anywhere in resolving the dispute over the Cooperstock & Lieu claim?

Garth

 

[SpaceTiger]

So what is the limit on DM is there in our neighbourhood?

I can't say anything about that yet, partly cause it isn't published and partly because I don't have an answer. Here's a decent review of some of the past results:

http://arxiv.org/abs/astro-ph/0203110"

And does this go anywhere in resolving the dispute over the Cooperstock & Lieu claim?

I doubt we'll check our results with their model.

 

[Garth]

I can't say anything about that yet, partly cause it isn't published and partly because I don't have an answer. Here's a decent review of some of the past results:
http://arxiv.org/abs/astro-ph/0203110"
I doubt we'll check our results with their model.

No - I didn't expect that you will! The question really is that if you have secondary confirmation of local DM from perturbations on the infalling stars then that would knock the nail on the Cooperstock & Lieu claim, as well indeed on the Milgrom/Bekenstein MOND hypothesis.

Garth

 

[SpaceTiger]

No - I didn't expect that you will! The question really is that if you have secondary confirmation of local DM from perturbations on the infalling stars then that would knock the nail on the Cooperstock & Lieu claim, as well indeed on the Milgrom/Bekenstein MOND hypothesis.

It's purely a dynamical test, so it wouldn't necessarily help discriminate dark matter from modifications to gravity. It's possible that their theories would give noticably different kinematics in the solar neighborhood, but we would have to do detailed models to say for sure.

 

[Chronos]

This is worth a look:

http://www.arxiv.org/abs/gr-qc/0601055
What do the orbital motions of the outer planets of the Solar System tell us about the Pioneer anomaly?

 

[Garth]

This is worth a look:
http://www.arxiv.org/abs/gr-qc/0601055
What do the orbital motions of the outer planets of the Solar System tell us about the Pioneer anomaly?

The paper sets out the present enigma: The Pioneer Anomaly cannot be explained by prosaic causes, gas or radiation leakage, and seems to be a real gravitational effect. This is seen in distant Pioneer and Voyager spacecraft , but there has been no correlating effect in the orbits of the outer planets.

It proposes a search for such an effect in the outer system asteroids/Kepler objects beyond 20AU.

One feature of the PA that I find intriguing is the magnitude of the PA acceleration is only just larger than the Hubble Acceleration cH, and therefore might well be cosmological in nature.

Garth