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I Dark Matter and Dark Energy Conundrum

  1. Dec 3, 2017 #1
    Question 1: Do the calculations/models for galactic structure, the basis for the missing 6x mass problem that created the notion of "Dark Matter," include any factor/variable or set of variables that account for space-time dilation due to relativistic effects caused by the super-massive black hole and associated vast collection of additional mass in the center of our galaxy?

    Question 2: Has there been any extensive survey of stars in the Milky Way assessing the hydrogen level (what generation) of stars in relation to their position/proximity to this black hole?
     
    Last edited by a moderator: Dec 3, 2017
  2. jcsd
  3. Dec 3, 2017 #2
  4. Dec 3, 2017 #3
    Thanks - but that article doesn't answer either of my questions. The article doesn't explain how she is doing the calculations, merely hints that she is looking at movements of clusters. I'll try to dig the actual publication out, but I think at the surface it ins't what I'm really after. I'm interested to understand how models of galactic structures came to a conclusion of missing mass, and I'd like to see how or if an effect from mass at the center of our galaxy was taken into consideration.
     
    Last edited: Dec 3, 2017
  5. Dec 3, 2017 #4

    Orodruin

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    The mass of the super-massive black hole, while large, is minuscule in comparison to the mass of the galaxy. Relativistic effects are only appreciable in the direct vicinity of the black hole and do not appreciably affect the physics behind the dark matter evidence. In addition, the evidence for dark matter does not only include galaxy rotation curves, but also things such galaxy clusters and structure formation computations.
     
  6. Dec 3, 2017 #5
    Is it about the type Ia supernovas and their distance to black hole which it might affect the redshift and hence the velocity that we observe ?
     
  7. Dec 3, 2017 #6

    PeterDonis

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    Is negligible on the scale of a galaxy. Run the numbers and see.
     
  8. Dec 3, 2017 #7
    Thank you - this helps a lot and does answer the first question.

    I'm still very interested to find an answer to the 2nd question, I suppose more of a general astronomy question.

    Arman, correct. My question is if there is a broad relativistic effect extending throughout the galaxy caused by the collective mass of the super massive black hole, accretion disk material and large collection of stars at the center of our galaxy rotating with a super high velocity. If there is, then yes, wouldn't this affect type 1a Super Nova magnitude as we detect it and have used for the standard candle measures. Folks here are commenting there is no appreciable effect. But I'd like to see an answer to question 2, if hydrogen content of stars has been examined and compared to their proximity to the center of the galaxy.

    thanks
     
  9. Dec 3, 2017 #8

    Vanadium 50

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    As mentioned in #6, there is not.
     
  10. Dec 3, 2017 #9

    PeterDonis

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    And the answer to this, as both I and @Orodruin have pointed out, is no.
     
  11. Dec 3, 2017 #10

    mfb

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    The hydrogen content of all stars is 75% at the time they form, slowly decreasing as they burn this hydrogen to helium. The surface hydrogen content can decrease slower than the core hydrogen content.
    75% is simply the fraction of hydrogen originating from the big bang. The other 25% are helium, and the remaining elements are a tiny contribution.
    This doesn’t depend on the location in the galaxy.

    By the way: We also have measurements of the amount of dark matter from the big bang - no galaxies, no black holes, no rotation curves. A completely independent measurement that agrees very well with the other results.

    It seems like you underestimate the amount of effort put into research. Whatever you can think of has been considered, and hundreds of things you don’t even know about have been considered as well.
     
  12. Dec 3, 2017 #11
    Is that the Russian measurements where they found 2-5% of an unstable dm variant from the bb in comparison with the PLANCK data?
     
  13. Dec 4, 2017 #12
    I thought about it then a question come to my mind

    Isn't this indicate that there must be a something that causes (could be DM or something else that we can see from planck result) the observational results ?
    Like I thought it can't be a modified gravity theory because our data comes from CMB, not from galaxies but then I did a bit search and I find something like this,

    "The Planck data thus demonstrate that not all is well with our understanding of cosmology, that is, the CMB poses hitherto unanswered problems. But even if the CMB had been in perfect agreement with the expectations from the current standard model of cosmology, what would this have implied for our physical understanding of cosmology?

    First of all, an elementary if not trivial truth is that consistency of a model with a set of data does not prove the model. Thus, claiming that Planck establishes the existence of (cold or warm) dark matter and dark energy would be an unscientific statement. For example, the cosmological model by
    (Angus & Diaferio (2011), http://adsabs.harvard.edu/abs/2011MNRAS.417..941A) shows that the CMB can be reproduced with a non-CDM/WDM model, therewith proving the non-uniqueness of the models." (from https://goo.gl/aoFHXL)

    Theres also other articles that says that DM models are wrong or etc (which you can find them in this page)

    I dont want to start a debate about DM exists or not. I know that theres also things wrong about LCDM model and there's some modified gravity models that tries to explain it etc.

    Returning to my question Can MOND explain the CMB ? (In other words, is this article makes sense or articles look like this, cause it seems to me there has to be some critical options to make it happen).

    If MOND cant explain CMB, cant we show us that is a strong evidence of that DM exist , and MOND theories are not acceptable ?
     
  14. Dec 4, 2017 #13
    This is exactly why I looked up this forum, joined and posted. In addition to the two questions I've posted here, I had a lengthy exploration of why/how I was asking the questions, but it was removed by moderators - that's fine, I wanted to just see responses to the base questions anyway.

    I'm a complete amateur, let me get this out right away. Somehow I've drawn ire from a few folks here, perhaps it was from my response in line 7 to Arman's question - I was trying to answer him, not discredit any other responses. In fact, I drew reference that several had already answered "there is no effect" -- or limited effect (paraphrasing). I get it. I sincerely apologize if I offended anyone.

    Now, what Arman is asking here, is exactly why I'm asking.

    How was DM confirmed in the non-galaxy, early big bang assessments? Was it based on light/luminosity/magnitude in any way? If our perception of galaxy structure, rotation, and our determinations of mass are all based (effectively) on luminosity, maginitude of star emission, then my questions are many. How did we actually come to determine the mass of the black hole and accretion disk matter and all nearbye stars by volume at the center of the galaxy? If we are using luminosity and magnitude as mass determinates, what would be the effect if our estimation of the black hole mass was off by 10%? 100%? 10,000%? If there was significant underesimation, then we would perceive much, much less mass from these stars in the inner orbit due to time dilation. the light path traveling would not be in a straight line, it would be on a steep curve due to the bending and warping caused by the black hole thus having the effect upon us the observer of less luminosity (therefore we would calculate less mass).

    That's largely why I'm asking question #2. If there has been any research on star chemical composition and their relation to the center of the galaxy, this might demonstrate this effect. My understanding was first generation stars have a higher percentage of hydrogen, and heavier particles are present in later generation stars. Perhaps I'm wrong about this as per MFBs comment on line 10. I was wondering, if a statistically significant study population of stars from close to the galaxy center, when compared to stars at the exterior, have a higher hydrogen content (they may not be first generation, but they could be earlier), then one explanation could be time dilation. If we are off on the calculations of the black hole and center galaxy mass calculations, wouldn't it be possible stars toward the center may be a fraction of the age as time-dilation has occurred, when compared to stars at the extremity of the galaxy where passing of time might be much, much faster.

    Again. TOTAL f*ng amateur here. I'm hear to learn. I absolutely respect research and that folks dedicate their lives and entire careers to solving much, much more complex problems than this one here. I'm just super curious to learn more about this, and each time I try to do my own research, anytime I find anything about how mass was calculated in the center of the galaxy for the black hole, or how distance was calculated (and red shift) for standard candles, magnitude of the star and luminosity was always a basis -- and I'm asking, because I'm a complete f*ng novice - could this be a weak link in measuring star mass, black hole mass and galaxy mass and rotation?

    Again, truly, truly sorry if I'm offending anyone here. My undergraduate work was not in physics, I have an elementary understanding of basic phyiscs and astro-physics. Thank you all for helping me to gain a deeper understanding - I'd welcome links to references, papers, things where I could read and understand this better.
     
  15. Dec 4, 2017 #14

    PeterDonis

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    The Wikipedia article gives a decent summary:

    https://en.wikipedia.org/wiki/Sagittarius_A*

    We aren't. We observe stars orbiting the central black hole and use their orbital parameters to determine the mass of the object they're orbiting. That is the obvious and most accurate way to determine the mass of something.

    As a separate comment, independent of whether the conditions you describe (stars orbiting far enough inside a supermassive black hole's gravity well for time dilation to be significant) actually apply in our galaxy (or any galaxy), your general analysis here is incorrect. The observed orbital periods of objects, as seen from far away (such as us on Earth observing stars orbiting the Milky Way's central black hole) are unaffected by time dilation; time dilation refers to the time that would be experienced by an observer who was co-located with the orbiting objects, not far away. Also, while light is indeed bent by the gravity of a black hole, that doesn't decrease observed luminosity of objects whose light is bent; if anything, it tends to increase it (look up gravitational lensing).

    Moreover, if we are talking about estimating the mass of a black hole, the hole itself emits no light and has no luminosity; and the luminosity of light emitted from things like accretion disks has no simple relationship to the hole's mass, and is not used to estimate the hole's mass.
     
  16. Dec 4, 2017 #15

    PeterDonis

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    You're mixing up two very different things. As I noted in my previous post, black holes have no luminosity, so you can't use luminosity to estimate anything about them.

    "Standard candles" are objects which have known absolute luminosities for a variety of reasons, so we can use their apparent brightness to estimate their distance. Two examples are Cepheid variable stars, which have a known relationship between period and absolute luminosity, and Type IA supernovae, which have a known fixed absolute luminosity because of the particular kind of process that produces them. None of this is used to estimate the mass of anything.

    There is a relationship between mass and absolute luminosity for various types of stars (the relationship differs depending on the type of star); so if we have some independent estimate of the distance to such a star (for example, using parallax), we can use its apparent brightness to obtain its absolute luminosity, and use that to estimate its mass. But it's usually not possible to get an independent estimate of distance.
     
  17. Dec 4, 2017 #16

    Chronos

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    Some of the most compelling support for DM has been provided by CMB and BAO data. By carefully measuring the tiny temperature fluctuations in the cosmic midrowave background, scientists were able to compile a graph known as the CMB power spectrum. The height of the first, second, and third peaks of the power spectrum tell the rest of the story. Note that this method of accounting does not involve any kind of preconceived mass luminosity relationship. For an overview of this method see https://ned.ipac.caltech.edu/level5/March15/Roos/Roos10.html. Another heavy hitter is offered by Baryon Accoustic Oscillation data, which was compiled by carefully measuring the angular separation and redshift distance of many thousands of distant galaxies. A summary of how this was used to infer the existence and mass of dark matter in the universe is discussed here: https://medium.com/starts-with-a-bang/what-the-hell-are-baryon-acoustic-oscillations-cfee6d726538. Once again, no preconceive notions about mass luminosity relationships are involved. Combining these two big guns with data from relatively simple supernova observations enabled scientists to pin down the DM content of the univers without resorting to any assumptions about mass luminosity as depicted here: https://ned.ipac.caltech.edu/level5/March15/Roos/Roos14.html.
     
  18. Dec 4, 2017 #17
    Excellent. Thank you all. This really helps. I have a lot to learn, exactly why I came here.
     
  19. Dec 4, 2017 #18

    Chronos

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    Modern cosmology has emerged as a true science because there is such a vast number of independent ways to corroborate our models of the universe with modern technology and methodology. This frees us from the tether of credibility imposed by reliance upon any particular hypothesis - such as mass luminosity relationships. Cross checking all these independent results is what earns us the confidence to so tightly constrain properties like dark matter. We are only forced to concede a few basic assumptions about the universe to lend our models credibility [e.g., the laws of physics are always the same irrespective of time or location in the universe]. While there will always [hopefully] be plenty of room to quibble over the details, it is enormously unlikely our big picture of the universe is substantially inaccurate.
     
  20. Dec 4, 2017 #19

    mfb

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    No, I mean the Planck measurements.
    You mean something like dark matter that causes the experimental measurements of dark matter?
    (a) it is a blog post by a PhD student
    (b) It is another example of a misleading comparison. Yes, you can find alternative models that fit to one specific measurement. You can fit galactic rotation curves with some version of MOND, you can fit the bullet cluster with another version of MOND, you can fit some structures in the CMB with time-dependent speed of light, you can fit this with that and that with this. But dark matter (or, more generally, ##\Lambda CDM## with inflation) is the only model that works reasonably well everywhere.
     
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