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Thread: Density wave in spiral Arm

  1. #61
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    Quote Originally Posted by Shaula View Post
    Lenticular galaxies don't have spiral arms. What features are you talking about when you talk about symmetry? The disk?

    Or are you talking about the grid you linked to? The grid that clearly doesn't show actual images of spiral galaxies but instead sketches of idealised shapes that are used as part of a galactic classification guide?

    I'm not speaking about the Lenticular galaxies.
    I'm looking at the arms of all spiral galaxies.

    They are all fully Symmetric with regards to the center.
    However, the orbital cycles of all stars are not symmetrical - it is elliptical.
    So how can we get a symmetrical spiral arms shape from none symmetrical stars orbital cycles?

  2. #62
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    You have not answered my question. What symmetrical shape?

    You also completely missed the point with the Zurich simulation. Again you are imposing your own beliefs on it rather than understanding the model (which I liked to examples of but, of course, you have not followed up on). The Zurich simulation didn't include any information about the orbits. It simulated them evolving from collapsing gas. It made no assumptions about the nature of the orbits or requirements for and end point. That is why it took so long to run and why it is such powerful evidence. The fact that you STILL don't understand that is a testament to your shabby treatment of any evidence presented to you. You refuse to take the time to understand it while simultaneously claiming it must be wrong for reasons you seem to invent on the fly and cannot back up. Instead you adhere to your beliefs or intuitions, ignoring evidence and theory that conflicts with them. I've never actually said this to anyone before in more than twenty years of ad hoc physics teaching but if you are not going to change how you approach this maybe you need to consider giving up. You will never understand the physics behind these things if you continue to behave as you are.

  3. #63
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    Quote Originally Posted by Dave Lee View Post
    They are all fully Symmetric with regards to the center.
    However, the orbital cycles of all stars are not symmetrical - it is elliptical.
    So how can we get a symmetrical spiral arms shape from none symmetrical stars orbital cycles?
    Right, so you are taking a sketch used for galactic classification and claiming it reflects reality.

    Google Spiral galaxy images. Your claims are demonstrably false for complex spirals. For simple spirals the first video I linked to shows you how this works for elliptical orbits.

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    Quote Originally Posted by Dave Lee View Post
    I'm not speaking about the Lenticular galaxies.
    I'm looking at the arms of all spiral galaxies.

    They are all fully Symmetric with regards to the center.
    However, the orbital cycles of all stars are not symmetrical - it is elliptical.
    So how can we get a symmetrical spiral arms shape from none symmetrical stars orbital cycles?
    Once again, you are making the huge mistake of believing that you have a valid intuition of how the physical world works. Stop it. Your self-confidence has been shown time and again to be woefully misplaced.

    A water molecule is asymmetric. How can it form symmetrical snowflakes?

    Think about it.

    Your intuition is almost completely useless because you haven't studied physics. One wonders if you have this same sort of unsupported self-confidence about your abilities at other activities you have never studied. You will never learn until you recognize that you are ignorant.

    Please stop.

  5. #65
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    The occurrence of disk galaxies without detectable spiral patterns shows that either they are not inevitable, or perhaps not permanent if they are inevitable in early stages. The British video that illustrated M51 showed a possible mechanism for "stirring the pot" in the form of perturbations by the companion.

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    Why do we claim that in the density wave there is about 10%-20% greater mass density?

    https://en.wikipedia.org/wiki/Density_wave_theory

    "The Lin-Shu theory introduces the idea of long-lived quasistatic density waves (also called heavy sound),[1] which are sections of the galactic disk that have greater mass density (about 10–20% greater).

    Is it only based on Lin-Shu theory?
    Did we also try to confirm it by the Simulation or by real measurements of mass between the arms?
    Last edited by Dave Lee; 2018-May-25 at 09:24 PM.

  7. #67
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    Quote Originally Posted by Dave Lee View Post
    Did we also try to confirm it by the Simulation or by real measurements of mass between the arms?
    Already covered in the Review of Density Wave Theory paper and Eris papers I have linked. If you look at the tests they applied your questions are answered.

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    Thanks,
    I didn't find it in the article:
    https://arxiv.org/pdf/1103.6030.pdf

    However, based on your answer, I understand that we have proved it by Simulation, and that is good enough for me.

    In the following article it is stated that the period Simulation is 13 Billion years.
    https://en.wikipedia.org/wiki/Eris_(simulation)
    "The motions of more than 60 million particles which represented dark matter and galactic gas were simulated for a period of 13 billion years.[5] The software platform Gasoline was used for the simulation."

    So, if I understand it correctly:
    At T0 (starting point of the simulation) there was no density wave (Greater mass density = 0%)

    Over time (simulated period) and as long as we set more and more orbital cycles around the galaxy, the density waves have been formed:

    At T1 we have got a greater mass density of only - 1%
    At T2 - 2%
    At T (13 Billion Years -end of the simulation) - 20% (max).

    Is it correct?

    If so, does it mean that as we set more orbital cycles, we get higher and higher mass density at the density wave?
    The current age of our Universe is only 13.8 Billion years.
    What is the expected mass density when the Universe will be at 26 Billion years, or 1K Billion Years?

    Is there any limit for the mass density value?
    Or technically, at infinite age, we might get a galaxy with 100% mass density at the density wave?
    Last edited by Dave Lee; 2018-May-26 at 05:48 AM.

  9. #69
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    Try the Review paper from post 46, it has a series of observational tests they use to highlight where the model is working and where there are discrepancies.

    The simulation situation is more complex as the formation of the density waves is dependent on the merger history in the simulation. It is more like:
    T(0) - overdensities are small and random and evolve randomly
    For each T(significant merger) - areas of correlated overdensity form, which may add to, reduce or be seperate from existing density waves
    T(later) - bar/ disk interactions add to the structure
    By T(13 billion) several significant mergers have happened, the bar is developed and a complex spiral galaxy has formed.

    Remember that there are a bunch of stochastic processes in the model - it isnt a simple, deterministic track from the start to the end. The goal of the simulation was not to create the Milky Way, it was to create a Milky Way like galaxy from realistic initial conditions using a realistic model.

  10. #70
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    Quote Originally Posted by Shaula View Post
    Try the Review paper from post 46, it has a series of observational tests they use to highlight where the model is working and where there are discrepancies.

    The simulation situation is more complex as the formation of the density waves is dependent on the merger history in the simulation. It is more like:
    T(0) - overdensities are small and random and evolve randomly
    For each T(significant merger) - areas of correlated overdensity form, which may add to, reduce or be seperate from existing density waves
    T(later) - bar/ disk interactions add to the structure
    By T(13 billion) several significant mergers have happened, the bar is developed and a complex spiral galaxy has formed.

    Remember that there are a bunch of stochastic processes in the model - it isnt a simple, deterministic track from the start to the end. The goal of the simulation was not to create the Milky Way, it was to create a Milky Way like galaxy from realistic initial conditions using a realistic model.
    Thanks for the excellent explanation.
    http://articles.adsabs.harvard.edu/c...;filetype=.pdf
    Now I have found it:

    "We found that 10 percent of the local mass is participating in the spiral arm, half from the gas and the other half from the stellar population. Clearly, the errors due to uncertainty in observations and the errors due to various approximations in the theory are unavoidable. Therefore, all the numerical values used in this paper may be subject to changes with the observational data and the galactic model to an extent of about 20 percent, but the qualitative features would be expected to remain the same."

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    With regards to the following questions:

    1. Does it mean that as we set more orbital cycles, we get higher and higher mass density at the density wave?

    If I understand you correctly, the answer should be - Yes.

    Please try to answer on the following:

    2. What is the expected mass density when the Universe will be at 26 Billion years, or 1K Billion Years?
    3. Is there any limit for the mass density value in the spiral arms?
    4. Technically, at infinite age, could it be that we might get a galaxy with 100% mass density at the spiral arm?

  12. #72
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    1. No. It all depends on the orientation of each perturbation event. The odds of direct, neat reinforcement is slight.
    2. Depends on the intraction history. Enough interactions and you don't have a spiral any more. Especially when you get to the point that whole galaxies of similar size merge.
    3. Probably. Remember that these are transient densities due to orbital convergence. Spiral arms don't rotate at the same speed as the stars that are in them at any given time. You can't have everyyhing in them.
    4. No. Long before that the disk will become highly distorted. Plus it is impossible to construct orbits that converge all the time.

    It sounds like you are thinking of the spiral arm as some kind of bound system again. It isn't. It is just a place where a number of correlated orbits converge. Remember the video of the idealised system? You cannot construct the overdensities in that without having mass in between these areas.

    Edit to add: also worth noting that "the density wave" might actually better be thought of as the superposition of lots of smaller essentially noninteracting density waves kicked up by different interactions.

  13. #73
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    It is my understanding that those density patterns are observed in real galaxies. The theorists test their theories by comparing the results of simulation runs with the observations.

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    Quote Originally Posted by Hornblower View Post
    It is my understanding that those density patterns are observed in real galaxies. The theorists test their theories by comparing the results of simulation runs with the observations.
    Thanks

    That is great Idea!

    There are about 2000 stars in a 50 LY sphere around the solar system.

    http://www.atlasoftheuniverse.com/50lys.html

    "There are roughly 1400 star systems within this volume of space containing 2000 stars"

    Based on our simulation the estimated mass density in the spiral arm should be greater by 10% to 20% comparing to the mass density outside the arms.
    Therefore, based on observation, we should find about 2000 x (90% or 80%) = 1800 to 1600 Stars in a similar sphere outside the arms.

    If I understand it correctly, our solar system is located at the inwards edge of the Orion spiral arm.

    The Carina Sagittarius arm is located only few K light away from our location.

    https://en.wikipedia.org/wiki/Milky_...y_Way_Arms.svg

    Let's set a virtual point exactly at the middle distance between our location and this Carina Sagittarius arm.
    Around this virtual point let's set a sphere with a radius of 50 LY.

    If we find there the expected 1800 to 1600 stars, then we can claim for full correlation between the simulation and observation.
    If no - we have to think about it.

    Any idea about that?
    Actually, do we have a list of all the nearby stars which are located outside the arm?
    Please be aware that we don't need a very sophisticated tool to discover those stars. They should be located directly in front of our eyes.
    Last edited by Dave Lee; 2018-May-26 at 02:27 PM.

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    Comparing two 50ly patches is a tiny sample size - especially without a scale dependent assessment of density variations. If you want to do this properly take multiple samples of this size and run some statistical tests. If you don't your conclusions will be completely unjustified, whether they support or oppose the theory. You also should not just consider stars. Consider all the mass out there including gas clouds. The analysis you are proposing is far too simplistic to give meaningful results.

    You might also want to not fixate on one test and look at several. For example traceback of open cluster formation, cold gas studies etc. All of these tests have been done and compared to predictions. Some results led to refinements of the model (for example the colour gradient that was predicted but did not occur on the edges of spiral arms). More suggested that the essence of the model is correct.

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    Quote Originally Posted by Dave Lee View Post
    Please be aware that we don't need a very sophisticated tool to discover those stars. They should be located directly in front of our eyes.
    You can only see around 133 of those 2000 stars with your eyes. Most of those stars are red and brown dwarfs that can only be detected with telescopes, and individual stars of any sort are increasingly difficult to detect with distance. And we can't measure the distance of distant stars with as much precision as we can near stars. And then there's the fact that our view of other parts of the Milky Way is obscured by all the other stars, gas, and dust in the disk, we can only get a clear view of other spiral galaxies. It's simply not possible to count the stars in some arbitrary 50 ly wide volume elsewhere in the galaxy and compare it to what's around us.

    What we can do is look at other galaxies, using views in multiple spectra to distinguish the varying numbers of different star types, concentrations of gas, etc. And that's the kind of thing that researchers are actually doing:
    http://scienceblogs.com/startswithab...13/09/gals.jpg

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    Quote Originally Posted by Shaula View Post
    Comparing two 50ly patches is a tiny sample size - especially without a scale dependent assessment of density variations. If you want to do this properly take multiple samples of this size and run some statistical tests. If you don't your conclusions will be completely unjustified, whether they support or oppose the theory. You also should not just consider stars. Consider all the mass out there including gas clouds. The analysis you are proposing is far too simplistic to give meaningful results.
    Yes, I agree that it's better to look at a wider radius scale.
    I also fully agree that we need to monitor any sort of mass including gas clouds.

    I have used the 50 LY as a reference as we have full measurements for this radius.
    If you wish to use 100 LY as a reference, that is perfectly ok.
    I don't want to fixate on one test and look at several.
    I also have no intention to trackback of open cluster formation, cold gas studies etc.

    I only want to look at a random place between the arms - in front of our Eyes - and monitor the Mass/Stars/Gas clouds at a sphere around this point.
    Why is it so complicated?
    The analysis which I'm proposing is very important. (Not just for me.)

    Somehow, it seems to me that you are too worried about this information.
    Could it be that there are no mass at all between the spiral arms?
    If there is - would you kindly help me to find it?

  18. #78
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    Quote Originally Posted by Dave Lee View Post
    I have used the 50 LY as a reference as we have full measurements for this radius.
    If you wish to use 100 LY as a reference, that is perfectly ok.
    No, what I mean is that just picking one location to sample is bad technique. It is bad stats and a bad piece of analysis. You need to do a proper density analysis using multiple samples from different places in your areas you want to test.

    Quote Originally Posted by Dave Lee View Post
    I don't want to fixate on one test and look at several.
    I also have no intention to trackback of open cluster formation, cold gas studies etc.
    So if you have no intention to look at other published test results how is that not fixating on your chosen one test?

    Quote Originally Posted by Dave Lee View Post
    I only want to look at a random place between the arms - in front of our Eyes - and monitor the Mass/Stars/Gas clouds at a sphere around this point.
    Why is it so complicated?
    The analysis which I'm proposing is very important. (Not just for me.)
    It is not that complicated. Your approach is simplistic. Your proposed study methodology is statistically unsound and not robust. Ergo any conclusion you draw from this is going to be invalid, whichever way it comes out.

    Your approach is similar to me going outside, looking down the road I live on and seeing no Ford cars - then using this data to claim that there are no Ford cars on any residential streets.

    I have to say that I don't regard this analysis as important. It is easier to do this for other galaxies as we are not hampered by being inside them. It is easier to do other tests of our models. Comparing two tiny areas of a galaxy we are inside is not important. And doing it properly for our galaxy is a much bigger piece of work.

    Quote Originally Posted by Dave Lee View Post
    Somehow, it seems to me that you are too worried about this information.
    Could it be that there are no mass at all between the spiral arms?
    If there is - would you kindly help me to find it?
    I'm not worried in the slightest. Why don't you have a quick glance at, say, M51 (Whirlpool galaxy - https://apod.nasa.gov/apod/ap130224.html) or NGC1232 (The Grand Spiral - https://apod.nasa.gov/apod/ap171226.html). See? Plenty of stars and other matter between spiral arms.
    If you are really desperate to do precisely the invalid test you want to then I am only going to point you to GAIA - you can get huge databases of star positions from it. I've already warned you, though, about how valid your conclusion will be unless you change your experiment plan.
    Last edited by Shaula; 2018-May-26 at 04:02 PM.

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    Quote Originally Posted by Shaula View Post
    I'm not worried in the slightest. Why don't you have a quick glance at, say, M51 (Whirlpool galaxy - https://apod.nasa.gov/apod/ap130224.html) or NGC1232 (The Grand Spiral - https://apod.nasa.gov/apod/ap171226.html). See? Plenty of stars and other matter between spiral arms.
    Thanks, but I have no interest in M51 galaxy.
    I don't want to find stars between the arms in a galaxy which is located at a distance of 23,160,000 Ly from us.
    Please remember that if we look at far end galaxy, we can't focus only on the spiral disc.
    We see the spiral arms with all the stars/gas clouds... which are located above and below the disc.
    How can we distinguish if those stars are located 20 K Light Years above/below the disc or directly on the disc between the arms, while we monitor them from a distance of 23 Million Light year? Is it real?
    Therefore, this data is useless!!!

    Don't you think that it's much more realistic to look for those stars nearby?
    We are located at the disc. we are located at the spiral arm.
    So, why can't we look for this important data in a distance of 2K light years away from us?
    Why would we prefer to look for an answer at so far location which can't give any valid data?

    Quote Originally Posted by Shaula View Post
    Your approach is similar to me going outside, looking down the road I live on and seeing no Ford cars - then using this data to claim that there are no Ford cars on any residential streets.
    Let me use a better example.

    Let's assume that we had been informed that in the city there are 10% to 20% more people density with regards to the people density in a nearby desert.

    How can we prove or disapprove this statement?
    We might think that the best solution is to set the size of the city and the desert and than count all the people in the city and in the desert and compare the densities.
    However, we also could just look for living people in the desert.
    if we don't see any person in the whole desert, why do we have to make all of this hard work?

    So, it should be very easy for us.
    Just try to find stars/gas clouds... between our location and the nearby arm.
    If we can't find any kind of mass, what should be the outcome???

    Quote Originally Posted by Shaula View Post
    No, what I mean is that just picking one location to sample is bad technique. It is bad stats and a bad piece of analysis. You need to do a proper density analysis using multiple samples from different places in your areas you want to test.
    .
    I'm with you.
    Please feel free to choose different places (between the arms) in front our eyes and set the proper density analysis using multiple samples.
    You are more than welcome to start with any location which you wish.

    However, instead of introducing that data, we discuss why this data is irrelevant.

    I'm quite sure that if there were Stars/Gas clouds/mass in front of our eyes - between the arms, you would introduce it immediately.

    Quote Originally Posted by Shaula View Post
    If you are really desperate to do precisely the invalid test you want to then I am only going to point you to GAIA - you can get huge databases of star positions from it. I've already warned you, though, about how valid your conclusion will be unless you change your experiment plan.
    Thanks

    Yes, I really want to see this data.
    Would you kindly advice the web site (as I only found the Gaia Royal Hotel...).
    Last edited by Dave Lee; 2018-May-26 at 06:06 PM.

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    Quote Originally Posted by cjameshuff View Post
    And then there's the fact that our view of other parts of the Milky Way is obscured by all the other stars, gas, and dust in the disk, we can only get a clear view of other spiral galaxies. It's simply not possible to count the stars in some arbitrary 50 ly wide volume elsewhere in the galaxy and compare it to what's around us.
    With regards to the Carina–Sagittarius Arm which is located inwards the Milky way;
    It is stated:
    https://en.wikipedia.org/wiki/Carina...agittarius_Arm
    "The Carina–Sagittarius Arm is one of the most pronounced arms in our galaxy as a large number of HII regions, young stars and giant molecular clouds are concentrated in it.[2]"
    So, if we see all of those stars in this nearby arm, why can't we find the other stars between our location and that arm?
    If it is too difficult for us, let's look for mass/stars between the Orion arm and Persues arm (which is located outwards from the Milky Way center)

  21. #81
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    Quote Originally Posted by Dave Lee View Post
    Thanks, but I have no interest in M51 galaxy.
    I don't want to find stars between the arms in a galaxy which is located at a distance of 23,160,000 Ly from us.
    Please remember that if we look at far end galaxy, we can't focus only on the spiral disc.
    We see the spiral arms with all the stars/gas clouds... which are located above and below the disc.
    How can we distinguish if those stars are located 20 K Light Years above/below the disc or directly on the disc between the arms, while we monitor them from a distance of 23 Million Light year? Is it real?
    Therefore, this data is useless!!!
    Wow. Another arbitrary excuse to avoid evidence. So now you are claiming that distant spirals that are face on are completely different, morphologically, to spirals we see edge on?

    Quote Originally Posted by Dave Lee View Post
    Don't you think that it's much more realistic to look for those stars nearby?
    We are located at the disc. we are located at the spiral arm.
    So, why can't we look for this important data in a distance of 2K light years away from us?
    Why would we prefer to look for an answer at so far location which can't give any valid data?
    As I said, we are inside the structure we are trying to study. That makes it more difficult. The data to do it is out there but finding a paper that happens to do exactly the test you are demanding is not easy. Presumably because it is not necessary and won't tell us much.

    Quote Originally Posted by Dave Lee View Post
    Let me use a better example.

    Let's assume that we had been informed that in the city there are 10% to 20% more people density with regards to the people density in a nearby desert.

    How can we prove or disapprove this statement?
    We might think that the best solution is to set the size of the city and the desert and than count all the people in the city and in the desert and compare the densities.
    However, we also could just look for living people in the desert.
    if we don't see any person in the whole desert, why do we have to make all of this hard work?
    This pretty much sums up what is wrong with your approach to statistics. I've pointed this out to you before.

    Quote Originally Posted by Dave Lee View Post
    So, it should be very easy for us.
    Just try to find stars/gas clouds... between our location and the nearby arm.
    If we can't find any kind of mass, what should be the outcome???
    I look forward as to why these are not good evidence:
    Star clusters between arms: https://www.nasa.gov/sites/default/f...go_rev_v05.jpg

    I am also getting quite tired of performing basic internet searches for you.

    Quote Originally Posted by Dave Lee View Post
    I'm with you.
    Please feel free to choose different places (between the arms) in front our eyes and set the proper density analysis using multiple samples.
    You are more than welcome to start with any location which you wish.

    However, instead of introducing that data, we discuss why this data is irrelevant.

    I'm quite sure that if there were Stars/Gas clouds/mass in front of our eyes - between the arms, you would introduce it immediately.
    No, Dave, I am not spending my free time working through data sets to produce evidence you will then decide is wrong for some reason. This has gone far beyond reasonable. You have so far dismissed theory, toy models, simulations, a reasonable number of observational tests of the models and evidence from other galaxies where we can see the structure more clearly. Instead you are fixated on your own concept of a test and insisting that other people have to do the work to provide you with the only evidence you have decided to accept. I'm not doing it. If you want to then you do it. The case had been proven beyond reasonable doubt.

    Quote Originally Posted by Dave Lee View Post
    Thanks

    Yes, I really want to see this data.
    Would you kindly advice the web site (as I only found the Gaia Royal Hotel...).
    Typing Gaia into Google and "Gaia creates richest star map of our Galaxy – and beyond - ESA" is result 5. In Bing "ESA Science & Technology: Gaia" is number 5. Typing "Gaia stars" into either gives all the information you could want about the satellite. Plus there is a thread on this forum discussing the data release in the Astronomy section.

    https://www.esa.int/Our_Activities/S...axy_and_beyond

    The data link is in the article as http://archives.esac.esa.int/gaia

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    http://charliehoey.com/threejs-demos/gaia_dr1.html

    That is about as good a visualisation as you are going to get. Notice - no matter how far out you go there are no huge empty gaps. There is the usual issues of detection selection bias etc. But if your notion that the spiral arms are all the stars and matter were true you'd see huge bands in the data. You don't.

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    Quote Originally Posted by Shaula View Post
    Typing Gaia into Google and "Gaia creates richest star map of our Galaxy and beyond - ESA" is result 5. In Bing "ESA Science & Technology: Gaia" is number 5.
    Unfortunately, the list returned by Google that you see is not the list that other people see. In particular, searching just for "Gaia" demonstrates what's called "the bubble effect". Google tracks you and your IP address and the searches and selections made from that IP address. Supposedly the items early in its list of results are those that it "thinks" you'll be most interested in. It is not the same list that others get when using the same search string.

    For example, although there are links to the ESA's Gaia web sites (there's more than one) in what I see, the specific link you mention isn't even on the first page for me. In particular, link #5 points to a youtube video about a search service named Gaia.

    Strangely, I've never used Google to investigate yoga, so I have no idea why it thinks I'd be interested in that.

    ETA: Aha! There were multiple network glitches last night and my Spectrum RoadRunner DHCP IP address has changed. I suspect that whoever had it before me was into that kind of thing.

    I don't use Bing, so I can't check what it does.
    Attached Images Attached Images
    Last edited by selden; 2018-May-26 at 07:12 PM.
    Selden

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    Quote Originally Posted by Dave Lee View Post
    With regards to the Carina–Sagittarius Arm which is located inwards the Milky way;
    It is stated:
    https://en.wikipedia.org/wiki/Carina...agittarius_Arm
    "The Carina–Sagittarius Arm is one of the most pronounced arms in our galaxy as a large number of HII regions, young stars and giant molecular clouds are concentrated in it.[2]"
    So, if we see all of those stars in this nearby arm, why can't we find the other stars between our location and that arm?
    If it is too difficult for us, let's look for mass/stars between the Orion arm and Persues arm (which is located outwards from the Milky Way center)
    My bold. It is a mystery to me as to why you think we don't find stars in the regions between the arms. Please explain.

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    Quote Originally Posted by Hornblower View Post
    It is a mystery to me as to why you think we don't find stars in the regions between the arms. Please explain.
    My explanation isn't fully correlated with the main stream.
    However, if there were stars, nearby - between the arms, don't you think that we had to find them very easily (Or at least, some of them)?
    How can we see so clearly all the stars in the Carina–Sagittarius Arm, but we can't see stars between the Orion and that arm?
    I would mostly appreciate to know even about one star which is located between our location and the Carina–Sagittarius Arm.
    No need for 1500 Stars between the arms. Only one star and only in front of our eyes (Just between the arms) - is good enough for me.


    Quote Originally Posted by Shaula View Post
    http://charliehoey.com/threejs-demos/gaia_dr1.html

    That is about as good a visualisation as you are going to get. Notice - no matter how far out you go there are no huge empty gaps. There is the usual issues of detection selection bias etc. But if your notion that the spiral arms are all the stars and matter were true you'd see huge bands in the data. You don't.
    Thanks Shaula

    I do appreciate your great support.

    However, this image is very complex. We even can't see the spiral shape.
    Therefore, I have no clue which one is in the arm and which one is outside
    Last edited by Dave Lee; 2018-May-27 at 07:51 PM.

  26. #86
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    Quote Originally Posted by Dave Lee View Post
    However, this image is very complex. We even can't see the spiral shape.
    Therefore, I have no clue which one is in the arm and which one is outside
    That is the point. You can't see the spiral shape. If your erroneous notion of completely empty space between the spiral arms were true you WOULD see it. Very clearly. You would see it as huge dark bands with no stars in it at all. What we instead see is a disk structure with stars spread throughout, the majority being near to the Sun because they are bright enough and have enough parallax to measure.

    Zoom out to a few tens of thousands of LY from the Sun. Pan around. You can see the disk structure. But you cannot see the spiral structure because, as people have been telling you all along, it is only a relatively small overdensity of stars. So we can see them. And we can see them easily.

    I note with resignation that you have chosen to ignore the WISE data clearly showing stars between the spiral arms.

    If you won't accept accept GAIA, or WISE, and you won't accept my explanations of the visualisations available I have no idea what the standard of proof you have decided is necessary is. Both data sets show stars where you are asking for evidence of them.

  27. #87
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    Quote Originally Posted by Dave Lee View Post
    No need for 1500 Stars between the arms. Only one star and only in front of our eyes (Just between the arms) - is good enough for me.
    This statement is evidently untrue. Shaula has given you not just one, but many millions of stars with their position identified by the most sophisticated instrument for that purpose that has ever existed (Gaia). And yet, that is quite clearly not good enough for you because in the same post you dismiss it.

    You have a preconceived (and erroneous) mindset that the Milky Way is a structure like some sort of intergalactic ninja throwing star, with only empty space between the 'blades'. You have been told over and over and over again that this concept that you (and only you) have is erroneous - we don't see it when we look at our own Galaxy and we don't see it when we look at ANY OTHER galaxy in the universe. We don't see it when we make models based on Newton's laws, even though you continually invoke Newton and Kepler to somehow underpin your fantasies.

    So, now it's time for YOU to put up or shut up. You are convinced that there is nothing but empty space between the spiral arm. So, show us. Show us these voids in space "in front of our eyes" where there is nothing but nothing between the arms in line with the disc. Show the entire scientific community why they are wrong and you are right.
    Go on - show us. We'll wait.

  28. #88
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    Quote Originally Posted by Dave Lee View Post
    My explanation isn't fully correlated with the main stream.
    Dave Lee,

    Then you need to be very careful. There is questioning the mainstream answers you are given so as to understand them better. But it seems apparent that you are questioning at least some of the answers you are given because they don't match your non-mainstream ideas. You need to stop doing that. Frankly, the Moderation Team is more than a little tired of your behavior.

    If you can't help arguing points that don't agree with your non-mainstream ideas, then maybe you should stop posting those arguments here.
    At night the stars put on a show for free (Carole King)

    All moderation in purple - The rules

  29. #89
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    Quote Originally Posted by Hornblower View Post
    My bold. It is a mystery to me as to why you think we don't find stars in the regions between the arms. Please explain.
    Quote Originally Posted by Dave Lee
    My explanation isn't fully correlated with the main stream.
    I am not asking about an ATM theory aimed at explaining such a void. I am asking about what sort of publications or other sources, if any, are causing you to believe that there are such voids.

  30. #90
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    Let me summarize:

    Zurich Simulation had proved that it is expected to see about 10% to 20% less mass density between the the arms (In the disc).
    Based on the mainstream, the orbital velocity of the stars is faster from the orbital velocity of the spiral arm.

    In the arm, near the Sun, the star density is quite high.
    Sooner or latter all of those stars (In Orion arm) should get out from the arm and new stars should take their place.
    Therefore, I have asked if we see the requested 10% 20% less density between the Orion arm and Sagittarius arm and Orion to Perseus arm.

    I couldn't understand from Shaula if we do see the requested densities between the arms near our location.
    If we don't see, than as the whole mass near our location (including the Sun), will shift out from the Orion arm, no real mass can replace it.

    This might be a contradiction to the Zurich simulation.

    However, as Shaula claim that this is OK, than I have no further question about this issue.
    Last edited by Dave Lee; 2018-May-28 at 06:08 PM.

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