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B Picture of "very" blue galaxy, good place for super nova?

  1. Aug 5, 2017 #1
  2. jcsd
  3. Aug 5, 2017 #2

    jim mcnamara

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    Playing Devil's Advocate: is this galaxy red shifted or blue shifted? Are the colors the result of some sort of post exposure processing - color enhancement?

    Those are questions I would ask... and your answer is....?

    BTW: interesting idea.
  4. Aug 5, 2017 #3
    Most galaxies are in general red-shifted because of the expansion of our Universe, right? So odds are it is red-shifted. Wiki says it has a redshift of 0.004657[2] so that means it is red-shifted I think.


    Is it blue or just processing, good question. I guess I need a power spectrograph of the galaxy to compare to many others. A google image search NGC-1398 shows some not so blue images.


    I wonder if there are astronomy databases available to students?

    Google seems to think yes, https://www.google.com/search?safe=...k1j33i22i29i30k1j33i21k1j33i160k1.iboIektoTe8
  5. Aug 5, 2017 #4


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    Why do you think the velocity of a galaxy relative to the Milky Way would make it more or less likely to be a good source of novae??? I cannot fathom your logic in this.
  6. Aug 5, 2017 #5
    If it turns out to be in fact a very blueish galaxy my thoughts are it is then a place of many young hot short lived stars that go boom!
  7. Aug 5, 2017 #6


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    Ah. I was looking at it from the point of view that a galaxy that is almost purely blue shifted could only be so by virtue of it being in the state of having a proper motion towards the Earth and this would have nothing to do with whether or not it is likely to form novae.
    Last edited: Aug 6, 2017
  8. Aug 6, 2017 #7
    I'm not sure about NGC 1398, but it seems void galaxies tend to be bluer as detailed in this paper:

    We look at the ur colours as an indication of star formation activity and the inverse concentration index as an indication of galaxy type. We find that void galaxies are statistically bluer than galaxies found in higher density environments with the same magnitude distribution.​

    Here's some info on the photo: http://skycenter.arizona.edu/gallery/Galaxies/NGC1398
  9. Aug 6, 2017 #8
    From the above link, "Exposure LRGB = 8:4:4:4 Hours", does such an exposure accurately reproduce an image of the galaxy, accurately in the sense that if we were near enough to see the galaxy NGC 1398 with the unaided eye the picture of NGC 1398 above would look like what we saw with our unaided eye?

  10. Aug 6, 2017 #9

    Vanadium 50

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    The star formation rate (and thus supernova rate) in NGC1398 is quite low: 0.11 Msun/year, or about 7% of what it is in the Milky Way. One photograph that looks blueish is not enough to tell
  11. Aug 6, 2017 #10
    If star formation rate were low but the proportion of large stars formed was greater we might still get a greater rate of super nova events then for an average galaxy?
  12. Aug 6, 2017 #11
    No to the unaided eye the galaxy would be a grey blob since it is not bright enough to trigger the color receptors in the eye. If you are close enough you might tease out some structure in the blob but that is about it until you get close enough to see individual stars. The reason is that surface luminosity is not affected by distance. If you want to do the comparison yourself go out and look at the Milky way and compare what you see it with the best images of the Milky way (e.g. https://apod.nasa.gov/apod/ap170203.html)
  13. Aug 6, 2017 #12


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    Not really. Even up close the galaxy would be nothing but a "fuzzy blob" of grey, much like how the milky way itself is a greyish streak across the sky and Andromeda is a greyish fuzzy blob, even in a telescope.

    More importantly, astronomical images are almost always processed in such a manner as to produce a visually pleasing picture, regardless of what the original "raw" exposures first look like. Many, especially those of nebulas, are entirely wrong in their colors. The "hubble pallet" used to make images from narrowband exposures uses blue to represent the oxygen-III emissions (which are in the blue-green area of the spectrum), green to represent the hydrogen-alpha light (which is actually very, very red), and red to represent sulfur-II emissions (which are slightly more red than the hydrogen-alpha).
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