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How much dark matter in each galaxy? Is it related to age?

  1. Sep 28, 2010 #1
    Does anyone know if there is an understood correlation between the amount of dark matter we suspect in a galaxy and the age of the galaxy?

    Basically, I am wondering if older galaxies tend to have more dark matter. But I need references to information on this, not just opinions :) Thanks.
  2. jcsd
  3. Sep 28, 2010 #2
    well i dont have time for referances but you question would relate to the longevity of stars.
    dark matter is only dark because we cant see it. We cant see dark matter because there no light (stars) to eluminate them. So if older galaxies have less stars then yes, more dark matter. I think radio telescopes can detect dark matter (theoretically)
  4. Sep 28, 2010 #3
    Thanks rhyshanan. That sounds like a good theory. You wouldn't happen to know if they have already observed this pattern at all though would you? or have a key-word to search on? I'm trying to determine if a correlation has actually been observed or not yet.
  5. Sep 28, 2010 #4
    Well the only way people know dark matter exists is because of the gravity dark matter creates. things around dark matter will have strange orbits that signal that there must be an invisible object close by with gravity influancing the observerd object.
    Our best telescopes can hardly see our own galaxy never mind other galaxies, so observing dark matter in distant galaxies is way out of our current capability
  6. Sep 28, 2010 #5
    From wiki
    In astronomy and cosmology, dark matter is matter that is inferred to exist from gravitational effects on visible matter and background radiation, but is undetectable by emitted or scattered electromagnetic radiation.[1]
  7. Sep 28, 2010 #6
    Thanks again. I see. I'm hoping someone will know if there was a connection between calculated age of galaxies and the amount of dark matter that has been calculated for them.
  8. Sep 28, 2010 #7
    Thanks. I was wondering if there is a known connection between the 'amount' of dark matter that is inferred by these gravitational effects and the 'age' of the galaxy. Basically, is age correlated to the the extent to which we suspect dark matter exists there. (ie. I'm not really asking about what is dark matter or anything close to that... just about the age vs amount of dark matter predicted)
  9. Sep 28, 2010 #8
    Yes I know, and I don't know the answer to that, I was merely correcting the assertions that we can't see dark matter because stars don't shine on them. Dark matter doesn't interact with electromagnetism.
  10. Sep 28, 2010 #9
    I'm trying to say our current level of technology does not allow for us to answer this question. Maybe someone else will have another theory like. bigger galaxy more dark matter, but it will just be a theory becasue there is no way to know with the technology we have
  11. Sep 28, 2010 #10
    I see. Thanks. I believe that observations have been able to detect the 'speeds' at which stars orbit the galaxy center. These speeds for some reason do not match the 'predicted' speeds that they should traveling. They are travelling 'faster' than they should, thereby implying that there is additional gravity involved. Based on the observed speeds, they can calculate how much extra gravity would be need to cause these speeds.

    So, based on what they do see of the speeds, they can estimate the amount of dark matter that exists there. The question is just, is this related to the age of the galaxy at all?

  12. Sep 28, 2010 #11
    Why not? You can measure the mass that should be there and the age of object and determine how much mass is seen, so you could find a correlation if there was one.
  13. Sep 28, 2010 #12

    i don't see how this is possble.
  14. Sep 28, 2010 #13
    Well you could look at the young, forming galaxies in the sky and compare them with the old galaxies. It's not an "age" per-say but it's relative.
  15. Sep 29, 2010 #14


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  16. Sep 29, 2010 #15
    Insufficient data to tell.

    One problem is that if you want to see really old galaxy then it's dim enough so that it's hard to get galaxy rotation measurements.
  17. Sep 29, 2010 #16
    Okay, thanks. That makes sense. I guess of the list of younger/brighter galaxies, are we able to determine the age of them precisely enough that we could see if there's a correlation? Or would the ages be too vague?
  18. Sep 30, 2010 #17
    This can't be right. One of the first anomalies to suggest the existence of dark matter came from observing rotation curves of other galaxies and finding that they rotate differently than expected for the visible distribution of matter. This sort of measurement could give us a handle on the amount of dark matter present. The only problem is that we wouldn't be able to get a range of galaxy ages, as younger (more distant) galaxies would be hard to resolve.

    And dark matter isn't simply dark because nothing is shining on it, it's fundamentally a different sort of matter.
  19. Sep 30, 2010 #18
    I'm sure I'd be ruffling a few feathers if I said that it is for this reason, combined with the 'winding problem' and its associated theory of 'gravitational waves' that I highly doubt dark matter exists at all.

    Basically, we observe speeds that suggest two big problems:
    1. Break Kepler's 3rd law
    2. Contradicts our idea of how old the galaxies are (since galaxy would up from many rotations, but doesn't)

    So, in order to preserve what we understand about our 'speed measuring' ability, we have had to come up with two new and unsubstantiated ideas to 'make it work.' I'm sure with some thought we could also come up with many other unsubstantiated theories to resolve the problems. I heard a grade one student suggest there are some bumblebees flying in space that keep moving the stars to new places.

    I think we need to be 2nd guessing our 'perceptions' of the speeds that we measure - even though we are so incredibly confident that these are accurate, I think this certainty ought to be less certain that our confidence in Kepler's 3rd law or the age of the galaxies, etc. It is possible to be more likely to have an error in measurements than to have new undetectable phenomena like Dark Matter or Gravitational Waves.

    In other words, we are really weighing one against the other: "Dark Matter/Gravitational Waves" versus "Accuracy of Measurements"
    Last edited: Sep 30, 2010
  20. Sep 30, 2010 #19
    That's a good point, lenfromkits, but there are plenty of other observations (unrelated to galaxy rotation curves) that support the notion of cold dark matter. Gravitational microlensing, for instance, has been used to map specific distributions of dark matter. However, I don't have the time or interest to go into full detail and get into a dark matter argument.

    You're right in that we should be skeptical and consider all possible models that fit the data. Fact is, the data we've collected to date points to a cold dark matter model. Astronomers all over the world have been looking at alternative possibilities for decades. People certainly have considered the things you mention.
  21. Sep 30, 2010 #20

    That is a good point too. In a sense, it says - "we do detect Dark Matter." But then it becomes a matter of weighing the "dark matter" versus "error in measurement" against each other. The 'winding problem' actually is a point on the side of "error in measurement" while the gravitational lensing is a point on the side of 'dark matter'..... so we're still even! ;)
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