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Thread: Spiral Galaxies: Stars move inwards with constant radial speed.

  1. #91
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    Quote Originally Posted by Jean Tate View Post
    OK, full disclosure: I have been actively hunting SDRAGNs (spiral galaxies with double (radio) lobe AGNs) for some time now, based primarily on Radio Galaxy Zoo. I lead a team working on finding and confirming them. In the literature, there are ~a dozen, and we have found perhaps another dozen (publication pending, as they say). Out of perhaps a million confirmed spirals.

    I have also been active in Galaxy Zoo...

    From this work, I can say with a very high degree of confidence that what you present is pure cherry picking....

    I may post some details of the work that has been done, work that is directly relevant to your idea, and which you seem to be unaware of (or have chosen to ignore).
    It would be interesting to see your work, but the cherry picking accusation isn't fair. GAIA (post 76) took time to find, but it happens to be the most up to date and accurate survey of Milky Way kinematics, if it shows a complex interplay of substantial inward and outwards radial motions including streaming, so be it. That's not cherry picking.

    Also mentioning that the Milky Way has enormous lobes which are also radio sources isn't cherry picking. We happen to live in a galaxy with such lobes. Why it's different for the ones you mentioned, who knows. But to claim that there isn't vast ejections from galaxies is probably more ATM than this ATM thread!
    "...when you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes

  2. #92
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    Here's the (key part of) the OP:

    The stars in a spiral galaxy are moving at approximately constant radial speed towards the galactic nucleus.

    It's at a similar value to the tangential speed, which is also approximately constant, (flat rotation curves), meaning that the stars move at constant speed towards the centre of the galaxy.

    It was the flat rotation curves which led to the 'dark matter' model, and dark matter is still required here.

    However, something there doesn't seem to have been much work on, is why dark matter takes on the particular distribution it needs to have to give the flat rotation curves. This very definite distribution lacks an explanation. The proposal here can explain this distribution, details soon.

    The proposal can also explain the spiral shape.
    From the Gaia DR2 paper you posted, it seems that your ATM model is ruled out.

    Also, your ATM idea seems to be quite unrelated to "vast ejections from galaxies"; can you remind me again please, what is the relevance to the explicit ATM model you posted early in this thread (post #3?)? (there are certainly "ejections", but "vast"? Like mass ~equal to the baryonic mass of the disk, every giga-year? or ~the mass of a typical GMC every 100 My?)

    Finally, re "why dark matter takes on the particular distribution it needs to have to give the flat rotation curves", in addition to what Shaula posted, you seem to have ignored (or are unaware of) the extensive work done to try to get a handle on this, empirically. For example, in today's arXiv, "Constraining the Milky Way Halo Potential with the GD-1 stellar stream", Malhan&Ibata (2018). How is work like this irrelevant to your ATM idea?

  3. #93
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    And as luck would have it, there's a Galaxy Zoo blog post (!!!) today with direct pertinence to this ATM idea: Finding Bars in Galaxy Zoo: 3D. Here's a part which is directly relevant:

    Itís been postulated that a bar can transfer matter (such as gas) radially inwards through a galaxyís disk and into its central regions.
    If a postdoc says that, you can bet there's a considerable literature on it, which you somehow seem to have missed, john hunter.

  4. #94
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    Quote Originally Posted by john hunter View Post
    It is you that is claiming that Newtonian gravity is violated in the orbits. ...
    I am claiming that any consideration of the Newtonian gravity that you are using for stars makes your ATM idea wrong and that you need to fix that flaw.
    A "loss in angular momentum to dark matter" guess without physics is not science. You imagining what may happen as in post 74 is not science.

    It is obvious to people who think about orbits of stars in that galaxy that there will be some, probably random galactocentric radial velocities [that cancel out and so invalidate your ATM idea].
    IF05: Where are your calculations of the orbits of stars including dark matter using Newtonian gravity that produce a "constant radial speed", john hunter?

    The probable answer is that you have none and so your ATM idea has a flaw that you need to fix. I suggest that you suspend the thread and do the work. This will also allow you to answer the question below.

    IF04: How closely do the galactocentric velocities in this paper match your ATM idea predictions, john hunter?
    Last edited by Reality Check; 2018-Jul-17 at 09:34 PM.

  5. #95
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    The ATM model says that matter moves inwards with a net constant radial speed for the flat part of the curve. e.g. if it's 20km/s at r=30kpc it's also 20km/s at r=15kpc and 20km/s at r=8kpc etc...that includes dark matter too.

    Quote Originally Posted by Jean Tate View Post

    From the Gaia DR2 paper you posted, it seems that your ATM model is ruled out.

    Also, your ATM idea seems to be quite unrelated to "vast ejections from galaxies"; can you remind me again please, what is the relevance to the explicit ATM model you posted early in this thread (post #3?)? (there are certainly "ejections", but "vast"? Like mass ~equal to the baryonic mass of the disk, every giga-year? or ~the mass of a typical GMC every 100 My?)

    Finally,...Malhan&Ibata (2018).

    [and from post 93] "It’s been postulated that a bar can transfer matter (such as gas) radially inwards through a galaxy’s disk and into its central regions."
    GAIA: post 76 shows complex radial motions, so it's going to be difficult to determine the net result and the ATM is not ruled out.

    Relevance of ejections: According to the ATM (as above) it's natural to wonder where all this matter is going. It must eventually be ejected from the centre if a stable dynamic equilibrium is reached. The rate of infall and hence rate of ejection (including dark matter) is vt^2*vr/G
    For a low vr of 1% vt, it would be about 30 solar masses per year.

    Re Finally: The link showed stars streaming in complex orbits with significant radial components. If such a stream were to 'run into' the Central Massive Object it would contribute significantly to the net inward flow.

    and Re "a bar can transfer matter (such as gas) radially inwards": That kind of thing could be part of the complicated inflow - that results in the net constant inflow, constant with radius (averaged over time and all matter).
    Last edited by john hunter; 2018-Jul-17 at 10:41 PM.
    "...when you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes

  6. #96
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    Quote Originally Posted by Reality Check View Post
    IF05 Where are your calculations of the orbits of stars including dark matter using Newtonian gravity that produce a "constant radial speed".
    IF05: It probably isn’t possible to do that. As shown by GAIA and things suggested by Jean Tate, in post 93, there are complicated and dynamic processes going on, the result of which is the net constant inflow.

    To repeat the advantages of the inflow:

    The spiral pattern may occur under certain circumstances.

    The m(r)/r = constant, occurs naturally for constant inflow, which gives the flat part of the rotation curve.

    The constant inflow meeting the constant density region, gives the right shape for a rotation curve
    Post 57 and link https://www.desmos.com/calculator/ys9xlui6cs

    A break will now be requested from the moderators.
    Last edited by john hunter; 2018-Jul-17 at 10:48 PM.
    "...when you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes

  7. #97
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    Quote Originally Posted by john hunter View Post
    The ATM model says that matter moves inwards with a net constant radial speed for the flat part of the curve. e.g. if it's 20km/s at r=30kpc it's also 20km/s at r=15kpc and 20km/s at r=8kpc etc...that includes dark matter too.



    GAIA: post 76 shows complex radial motions, so it's going to be difficult to determine the net result and the ATM is not ruled out.

    Relevance of ejections: According to the ATM (as above) it's natural to wonder where all this matter is going. It must eventually be ejected from the centre if a stable dynamic equilibrium is reached. The rate of infall and hence rate of ejection (including dark matter) is vt^2*vr/G
    For a low vr of 1% vt, it would be about 30 solar masses per year.

    Re Finally: The link showed stars streaming in complex orbits with significant radial components. If such a stream were to 'run into' the Central Massive Object it would contribute significantly to the net inward flow.

    and Re "a bar can transfer matter (such as gas) radially inwards": That kind of thing could be part of the complicated inflow - that results in the net constant inflow, constant with radius (averaged over time and all matter).
    I am now thoroughly confused as to what the ATM idea is, and what it isn't.

    That there is "secular evolution" in disk galaxies (not just spirals) is thoroughly mainstream ... left alone, disk galaxies' morphologies will change, and the distribution of mass - particularly "gas", but also stars - will change too. Some of that will surely involve "a net constant radial speed" at least some of the time (though it may, or may not, be ~comparable to "for the flat part of the curve"); some of it not. That "mergers" - minor or major - will produce streams which persist long after the obvious gross morphology has gone is also thoroughly mainstream, ditto that some of those streams will be found within disks.

    Complex motions may have a "net radial component"; how will you analyze data like that found in Gaia DR2 or MaNGA to estimate what is the net is (whether radial or not)?

    What criteria will you use to determine/decide if your ATM idea is consistent with all relevant data?

  8. #98
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    Quote Originally Posted by john hunter View Post
    IF05: It probably isnít possible to do that.
    That is a fatal problem with your ATM idea. If it is nor developed enough to back up its assertions with physics then it is fairly useless in its current state.

    The rest of your post:
    1. A spiral pattern is still trivial and irrelevant. Imagine that stars have a "constant radial velocity" and an orbital speed. Of course they will spiral in.
    2. Guessing that "m(r)/r = constant" gives the flat part of galaxy rotation curves is not science, especially when galaxy rotation curves need not have a flat part.
    3. Post 57 does not derive a galaxy rotation curve from your ATM idea.
    4. https://www.desmos.com/calculator/ys9xlui6cs is not an galaxy rotation curve !

  9. #99
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    By the request of the OP, this thread is temporarily closed, to give john hunter time to catch up on some research and reflection.

    john hunter, when you are ready to continue, please report this post. And yes, you may reference your previous thread when you restart.
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