Do voids in the Universe influence the orientation of galaxies?

[turbo]

About how bad science journalism is in relation to cosmology, there is this very unhealthy obsession over "what happened before the big bang" and barring something really weird, I doubt there is going to be much progress on that over the next two years.

I tend to ignore most of that stuff, like collapse, bounce, multiverse, etc. It makes for lively reading, I guess, judging from the number of articles that get cranked out.

 

[twofish-quant]

In MOND, the constant G still is a constant as far as I know (there may be other flavors), though it is assumed that the forces derived from Newtonian dynamics do not hold in low-acceleration regimes.

There have been tons of different versions of MOND. If you assume that things are an inverse square law, and that you are just changing G by a constant everywhere, then you end up with something that clearly won't work, because if you change G by a constant everywhere, then stellar evolution models go bonkers. Even very small changes in G means that stars burn brighter and dimmer.

So just rescaling G everywhere by a constant won't work, so you have to have variable G that depends on different things, and at that point any changes in G can be folded into the gravity law. Take whatever rule you come up with divide it by a r^2, and that's your variable G.

One thing that about modified gravity models is that they are all at the "curve fitting" stage. People are just trying to get some consistent rule that works, and they've had not much success at this. No one really knows or really cares right now what causes gravity to behave diferently. That's one big strike against modified gravity models.

It's reminiscent of the old saying that democracy is the worst system of government except for anything else. You can say the same with LCDM. If you look at it in isolation is looks ugly, ad-hoc, with lots of weird unjustified assumptions. Point taken. It's just that no one has come up with anything better, and it's not for lack of trying.

 

[turbo]

One thing that about modified gravity models is that they are all at the "curve fitting" stage. People are just trying to get some consistent rule that works, and they've had not much success at this. No one really knows or really cares right now what causes gravity to behave diferently. That's one big strike against modified gravity models.

At least MOND had a predictive success, with the galaxy rotation curves of LSBs falling nicely in line. That is encouragement for the modified-gravity crowd because it hints that some phenomena can be modeled without DM and that perhaps a more general law could be derived with a greater range of application than individual galaxies.

 

[Astronuc]

From the OP, the new structure or part of the structure is at ~7 billion ly or 2 Gpcs. Is this the furthest discovery of the web structure? Or does this just fill in a hole in the currently known web structure?

A&A 505, L9-L12 (2009)
DOI: 10.1051/0004-6361/200912929
Letter
The spectroscopically confirmed huge cosmic structure at z = 0.55
http://www.aanda.org/index.php?option=article&access=doi&doi=10.1051/0004-6361/200912929

 

[twofish-quant]

At least MOND had a predictive success, with the galaxy rotation curves of LSBs falling nicely in line. That is encouragement for the modified-gravity crowd because it hints that some phenomena can be modeled without DM and that perhaps a more general law could be derived with a greater range of application than individual galaxies.

MOND has one predictive success. LCDM has about three that I can think of off hand. (CMB anisotropy, helium abundances, and the existence and location of acoustic peaks). Also with CMB and galaxy structures, LCDM has much more detailed predictions than MOND. Also, if the LHC comes up with evidence for a particle that matches what LCDM requires, that will be a pretty big predictive success. LCDM requires a pretty big tooth fairy, but if you start seeing wings flapping and pixie dust, the fact that someone made such as outrageous prediction that seems to have evidence to support it, it quite an achievement.

As far as MOND, the fact that you got *something* is why people are working on it. Once you pull a rabbit out of the hat, people start taking notice. Again a lot of this involves, just keep plugging away and well see if it works or not. It's also not either/or. One thing that you have to be careful as a theorist is not to fall too much in love with your own ideas, since you don't determine what is right or not, nature does, so it's pretty common to spend five years or so working on a theoretical framework that turns out to just not work out in the end. But getting things to the point where you've managed to convince yourself that what you've been working on for five years is *NOT* the answer is quite a major and difficult accomplishment, and usually you end up with a lot of stuff that you can salvage for something else.

There is the possibility that you need *both* dark matter and MOND to make everything work out.

The problem with MOND is that it's pretty useless right now for the problems I'm interested in. I'm interested in gas dynamics, and LCDM gives people a framework to do gas dynamic calculations whereas MOND does not. However, it's not a waste to use LCDM as a paradigm even if it turns out to be wrong. If it turns out that modified gravity is correct then at some point someone is going to have to come up with an explanation for why the world *seems* like it has dark matter, and at that point it should be possible to take all of the theoretical work that has been done with LCDM and "translate" it into modified gravity.

 

[turbo]

However, it's not a waste to use LCDM as a paradigm even if it turns out to be wrong. If it turns out that modified gravity is correct then at some point someone is going to have to come up with an explanation for why the world *seems* like it has dark matter, and at that point it should be possible to take all of the theoretical work that has been done with LCDM and "translate" it into modified gravity.

Exactly! There has already been a lot of work done estimating cluster masses and peculiar motions so that the "missing mass" can be quantified. If modified gravitation shows promise, that work is directly transferable.

 

[turbo]

From the OP, the new structure or part of the structure is at ~7 billion ly or 2 Gpcs. Is this the furthest discovery of the web structure? Or does this just fill in a hole in the currently known web structure?

A&A 505, L9-L12 (2009)
DOI: 10.1051/0004-6361/200912929
Letter
The spectroscopically confirmed huge cosmic structure at z = 0.55
http://www.aanda.org/index.php?option=article&access=doi&doi=10.1051/0004-6361/200912929

That structure is at z~0.55, but there have been other examples of LSS at higher redshifts. It's really old news, in astronomical-research terms, but in 2002, Venemans et al reported the discovery of a protocluster (excess of lyman alpha emitters) surrounding a radio galaxy at z~4.1.

http://www.iop.org/EJ/article/1538-4357/569/1/L11/16078.web.pdf?request-id=0828b6d3-39ca-4d17-b4e2-ec9b6f9ad5a2

 

[lopkiol]

This? http://engweb.swan.ac.uk/~gabbriellir/javaview/wp-foam.html"

 

[matt.o]

6dF turned up a void 3.5 billion light-years across, so there is currently evidence of large-scale structure at least that large, and there may be much larger structures that we can observe, given improvements in instrumentation, including better optics and greater detector sensitivity. With voids framed by filaments and walls of galaxy clusters, the distribution of matter in space takes on a foamy appearance. A challenge for modern cosmology could arise from the discovery of structures on larger and larger scales, because the formation of structure through gravitational accretion takes time, and the Big Bang theory contains a self-imposed limit on the time available in which structure can form.

Do you have a link to a published paper for this ~1Gpc scale void found in the 6dF survey?

 

[turbo]

Not a peer-reviewed paper, though I'd be very surprised if John Huchra hasn't already published on or has on in the works. I'll take a look.

http://www.newscientist.com/article/dn16903-new-cosmic-map-reveals-colossal-structures.html

Scientists are still analysing the new map, but a few features stand out immediately. The biggest concentration of matter seen by the survey is a previously known giant pileup of galaxies called the Shapley supercluster, which lies about 600 million light years from Earth.

The survey also found some enormous voids – regions of space that are relatively empty, including one that is about 3.5 billion light years across.

"This is as big as I've ever seen," survey team member John Huchra of the Harvard-Smithsonian Center for Astrophysics told New Scientist.

Another large void about 1 billion light years across was discovered previously.

 

[matt.o]

Not a peer-reviewed paper, though I'd be very surprised if John Huchra hasn't already published on or has on in the works. I'll take a look.

http://www.newscientist.com/article/dn16903-new-cosmic-map-reveals-colossal-structures.html

Hmm. They don't give any details whatsoever in that article. I couldn't see any papers with Huchra as a co-author on ADS either, however Huchra may have just been approached for comment and may not have been part of the discovery. I'll wait for the paper to come out before commenting further or drawing strong conclusions.

 

[twofish-quant]

I couldn't see any papers with Huchra as a co-author on ADS either, however Huchra may have just been approached for comment and may not have been part of the discovery. I'll wait for the paper to come out before commenting further or drawing strong conclusions.

The other thing is that Huchra is an observationist and not a theoretician. He is a very good observationist, but I wouldn't immediately conclude that there really is a major problem based on an off-hand comment in a general journal.

 

[turbo]

I haven't found a link to a free version of this paper, so I can't vouch for the methodology, analysis, etc, but these authors claim that spiral galaxies on the edges of voids have rotational axes that lie preferentially on the void surfaces. Could be interesting.

http://www.springerlink.com/content/tk02015561k5573h/