Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

A Gravitational lensing

  1. Sep 6, 2016 #1
    Hi there. Have been doing some informant l independent research on gravitational lensing. It turns out that all einstein runs are blue. Why Is this?
     
  2. jcsd
  3. Sep 7, 2016 #2

    Chronos

    User Avatar
    Science Advisor
    Gold Member

    I assume you realize colorization of images is purely a dramatic effect..
     
  4. Sep 7, 2016 #3

    Chalnoth

    User Avatar
    Science Advisor

    I don't think all Einstein rings are blue. But far-away galaxies tend to be intrinsically bluer than nearby ones, as galaxies in the early universe were younger and had a lot more star formation. More star formation means a higher abundance of massive stars, and massive stars tend to be both bluer and brighter.
     
  5. Sep 7, 2016 #4

    Chronos

    User Avatar
    Science Advisor
    Gold Member

  6. Sep 7, 2016 #5

    Chalnoth

    User Avatar
    Science Advisor

    Skimming the paper, I don't think it's saying this. Rather, they're proposing a novel modification of General Relativity that makes Einstein rings blue. I'm not confident that this modification is necessary or that there is evidence for it.
     
  7. Sep 7, 2016 #6

    Drakkith

    User Avatar

    Staff: Mentor

    I agree. A cursory examination of google images showed several that appeared distinctly yellow. However, I will say that most of them appeared to be blue though.
     
  8. Sep 8, 2016 #7

    Chalnoth

    User Avatar
    Science Advisor

    No doubt. I really think it's down to these being predominantly young galaxies, but I have had a hard time coming up with any good sources for this.
     
  9. Sep 9, 2016 #8
    No they are blue unless redshifted. otherwise always blue as is described in this paper that makes an attempt at answering why. http://arrow.dit.ie/engscheleart2/19/

    There seems to be no good theory as to why though.
     
  10. Sep 9, 2016 #9

    Chalnoth

    User Avatar
    Science Advisor

    That's the same article that's linked above. It doesn't provide actual evidence (e.g. spectra), just a general statement that Einstein rings tend to be blue. It's a purely theoretical paper, which is fine. But it doesn't count as a solid explanation without confirming evidence.
     
  11. Sep 10, 2016 #10
    No it isnt. They are seen to be blue in the visual range and given an arbitrary colour if not in visual range.

    Is this opinion or can you cite. Because the only citation we have says they are always blue unless redhifted or they're in the visual range.



    If they are not blue then the photograph was not taken in the visual range and the colour is arbitrary.

    Alot of arbitrary guesses here does anyone have any useful information or citations?

    It seems to me odd that there wouldnt be considering the whole theory behind gravitational lensing rest son the absence of chromatic abberation, which doesnt appear to be the case as far as i can see.
     
  12. Sep 10, 2016 #11

    Drakkith

    User Avatar

    Staff: Mentor

    Seems to me that you can see it right in the pictures of all gravitationally lensed objects. We don't see different colors being focused at different ranges like a normal chromatic aberration. The only thing odd here is that some gravitationally lensed objects appear to be bluer than they should be.
     
  13. Sep 10, 2016 #12
    Infact we don't see different colours at all we only see blue unless redshifted or not in visual range. Unless you can cite a paper that says otherwise. The only one we Have so far agrees with what i Have said above.

    You could get this phenomena with normal chromatic dispersion. When shining a white light through a Crystal onto a distant wall the gap between colours would get wider. If you where an ant on one point of that wall it is possible that all you would see Is blue.
     
  14. Sep 10, 2016 #13

    Drakkith

    User Avatar

    Staff: Mentor

    Maybe. I don't know enough to argue further.
     
  15. Sep 10, 2016 #14

    Chronos

    User Avatar
    Science Advisor
    Gold Member

    Einstein rings are usually not imaged in visible light ranges, so they obviously must be colorized to render them viewable. According to https://en.wikipedia.org/wiki/Einstein_ring, "... Most rings have been discovered in the radio range." The number of 'optical' Einstein rings is relatively small. For a listing, albeit somewhat dated, see http://science.nasa.gov/science-news/science-at-nasa/1999/ast14may99_1/. Note that the ACS imager aboard the Hubble [see https://www.spacetelescope.org/about/general/instruments/acs/ for technical specifications] used to capture the photos shown is sensitive well beyond the visible range [450-700nm] so it is reasonable to expect at least some of these images are 'enhanced' [colorized] to bring out their more interesting features, much in the same way CMB maps are 'enhanced'. I doubt the sample size of optical data is large enough to permit any reliable conclusions about the apparent 'blueing' of lensed images. On this basis, it could be argued it is little more than an interesting curiousity, although the explanation offered in the IAENG paper looks plausble to me. For further discussion http://hubblesite.org/hubble_discov...nstein_rings_natures_gravitational_lenses.pdf may be of interest.
     
  16. Sep 11, 2016 #15

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    This thread is hopeless. The images you see on the web are all false color. (The so-called science images are not: those are monochromatic with a filter. But there simply are not any true color images taken of these objects.)

    The OP denies this in #10. Once you deny the data, it's not science any more.

    Now, if the OP were to provide a catalog of lensed object with a quantitative measure of their color, such as B-V, we can discuss whether such a thing is true.
     
  17. Sep 11, 2016 #16

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    PS Here's what I tried to write in the other thread:

    It is not a fact. Virtually every image you can find on the web is in false color. These galaxies are blue because some human being decided to make them blue. Before determining why something is true, one should first determine if it is true.

    Now, if you have a database of lensed galaxies with actual colors (e.g. B-V) we can discuss those. Do you?
     
  18. Sep 11, 2016 #17

    PeterDonis

    User Avatar
    2016 Award

    Staff: Mentor

    Thread closed for moderation.

    Edit: this thread will remain closed
     
    Last edited by a moderator: Sep 12, 2016
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Gravitational lensing
  1. Gravitational lensing (Replies: 4)

  2. Gravitational lensing (Replies: 7)

Loading...