Galaxies Definition and 416 Threads

http://arxiv.org/pdf/astro-ph/0501478 2 to 4 times more galaxies than expected found at z=5.9 how does this fit with cosmological models?

In the nucleus of a spiral galaxy the most stars are old population II stars, and there is no star formation (which occurs in the spiral arms). Why? Thanks.

Question: When Galaxies are being drawn into clusters, does expansion of the universe enter into the equation? In other words, does expansion effect clustering? :shy:

My understanding is that dark matter surrounds a galaxy in a spherical formation. What I don't understand this type of dark matter can explain the non-Kepplerian rotation of the galaxy. According to Gauss's law, in a spherical shell, only the mass inside the orbit of a body has a net...

This is just an idea but if galaxies have or develop a black hole in their center couldn't it be possible that darkmatter uses the electromagnetic field of the black hole to keep the galaxy in place and also keeps it from colliding with another galaxy. I can't really explain what i am thinking...

Is gravity so weak because every force mediating boson starts out as a graviton, which then loses energy and becomes gluons,photons W and Z particles. This would mean that the graviton carries colour charge and so dark energy must emit gravitons with colour charge and therefore dark energy...

Galaxies are all relatively the same size, ranging from a few thousand light years in diameter, to a hundred thousand light years or so. There seems to be some factors involved as to how large they can become, although I’m not sure it has anything to do with mass? Can someone please explain...

Does the path of light from distant galaxies curve according to with or without dark matter and energy?

How do we know that physics in distant galaxies is the same as we observe here on Earth? Do we just assume it's so, or can we do some experiments, make some observations to test the idea? In the last decade or three, quite a few tests of the idea have been done; an example discussed recently...

Another "new" release from NASA. Just click to join and you'll get these every day. So, I won't post these anymore. This subject has been discussed here on PF before, but this release should answer some of the questions asked...

I have some trouble seeing these two things. Let's say the big bang did happen, and the universe is expanding... ie all galaxies are moving away from each other. If all galaxies are moving away from each other, how can two gallaxies collide? Also... If again the big bang happened, and the...

Researchs show that our universe is expanding very fast. But I have also read that galaxies are racing ahead at great speeds on their way to collission with each other. If universe is expanding, then how come this is possible?

Sorry if this doubt has been posted anytime before, but in a little view I have not seen it! (well, I have not make an exhaustive search, it could take long time!). I think this doubt must be easy to resolve: So, we have two galaxies, A and B, and they are moving... If we are at A, we can say...

There's contantly discussion about if the universe is infinite in size or not. I want to pose the question in another way: Is the number of galaxies infinite? My answer: No

Thank's to the help I've received here I've created rules to turn the polar coordinates into cartesian coordinates but, say I had the coordinates for the galactic centre for Andromeda and the Milky Way and I also had coordinates for certain stars. I want to put a limit on my database that not...

Hi again, I'm doing a bit of research about the positioning of the galaxies (the local group in particular) and I was wondering if there were any lists available where the cartisian coordinates were already calculated as apposed to translating them from the polar coordinate vectors.