What is a "Cached image"?

What information is provided by the Hubble Ultra Deep Field 2012 infrared photo, and what are the details of procedures used to obtain the image?

• http://www.nasa.gov/mission_pages/hubble/science/galaxy-census.html Here are some specific questions I have about the above photo: What are the larger, brighter objects in the photo? Are there any galaxy clusters in the image? Why are there some objects with a four-point starburst, rainbow colored pattern? Would all of the red-colored galaxies appearing in the image be invisible if this image was made with a visible light camera? Are the blue-colored galaxies blue-shifted and moving toward us, or is the color just a result of blueshifting the entire image in order to make the red-shifted infrared galaxies visible? What is the specific frequency (or wavelength) change used in order to make invisible redshifted galaxies visible when we look at an infrared image such as this? How is Hubble able to take such a long exposure image without blurring since the telescope is traveling in earth orbit? Does redshift translate directly into both recessional speed and distance in every case? If not, what are the exceptions. Given that a redshift of 11.9 places a galaxy at a distance of 13 billion light years from us, how much further away is it likely that the galaxy has traveled in the time since the light that we see was emitted? Is there any indication in this image that the population of galaxies thins out near the edge of the universe (i.e. the inflation envelope)? Could this image have been obtained from a ground-based telescope, or would the atmosphere absorb too much of the infrared radiation? Do we expect to see a similar distribution of galaxies in all parts of the sky, or is there an area that we know is sparsely populated and therefore dark?

• Answer:

  Before I answer as much as I can, I must point out that I have only been interested in cosmology and astrophysics for a few months, and have never studied it formally. But seeing as there are no answers as of yet, I will just do my best, and then someone can build/edit on my post. 1. These objects are elliptical galaxies (An ellipse can also be a circle, which is why they can also be circular, as in the picture). They are usually the largest, and oldest galaxies. 2. I do not know, but I am quite sure there are not. 3. These are stars. Those spikes are typically there because of an optical defect. Not that Hubble is damaged, but you need specialized. equipment for star-pictures, which they could not use for the deep field, since it would remove a lot of detail from the galaxies (I think). 4. Yes, most likely. The visible light spectrum is 1000 times smaller than the infrared spectrum, and will likely not show much, if any, of the light emitted from these galaxies etc. 5. I do not know. I don't see any blue, though. 6. I don't have any experience with that. 7. Well, the HUDF is a mosaic image, composed of a lot of pictures. Most of them are taken with exposures of 21 minutes. 8. I think redshift could also explain the expansion of the universe, which of course makes the galaxies move away from us. 9. No idea. 10. It is not the edge of the universe, but merely the edge of the observable universe. The expansion of the universe, would create distance between the galaxies. 11. It would be impossible, but I need someone else to explain why. 12. https://en.wikipedia.org/wiki/List_of_voids I hope this helps, despite my inexperience. It might be too ambitious, though.