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

  1. #61
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    That was what the filament/streamers suggestion was about, but has been dropped due to lack of details. It was just a suggestion really, to show that if, for any reason, there was a region of increased density at the outer regions of the galaxy, - it would spiral in, increasing in density as it did so, and be a region where star formation was more likely.
    "...when you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes

  2. #62
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    Quote Originally Posted by Jean Tate View Post
    For avoidance of doubt, those four questions are not rhetorical; I look forward to your answers.
    The Q&A questions was not the full extent, there was an extensive search on the internet and arXiv, which came up with the three papers linked in post 31, which showed a substantial radial velocity both towards and away from the centre of the galaxy. Here is part of post 31 again.

    "There is some evidence here:
    https://arxiv.org/abs/0803.1826 Fig 6 page 38 and Table 5 pg 59, especially column Vavg

    and https://arxiv.org/abs/1805.00275 Fig 1 page 2 and Fig 10 page 7

    and https://arxiv.org/abs/1006.0064 Fig 4.2.1 page 45, which shows stars moving in highly elliptical orbits. These three papers show that there are stars in the bulge moving in highly eccentric orbits with one star measured with radial velocity of over 400 km/s."

    Currently looking into RAVE and awaiting Tusenfem's or the moderators response to private emails, or of post 55.
    "...when you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes

  3. #63
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    Quote Originally Posted by john hunter View Post
    The Q&A questions was not the full extent, there was an extensive search on the internet and arXiv, which came up with the three papers linked in post 31, which showed a substantial radial velocity both towards and away from the centre of the galaxy. Here is part of post 31 again.

    "There is some evidence here:
    https://arxiv.org/abs/0803.1826 Fig 6 page 38 and Table 5 pg 59, especially column Vavg

    and https://arxiv.org/abs/1805.00275 Fig 1 page 2 and Fig 10 page 7

    and https://arxiv.org/abs/1006.0064 Fig 4.2.1 page 45, which shows stars moving in highly elliptical orbits. These three papers show that there are stars in the bulge moving in highly eccentric orbits with one star measured with radial velocity of over 400 km/s."

    Currently looking into RAVE and awaiting Tusenfem's or the moderators response to private emails, or of post 55.
    Thank you.

    From your last sentence, I infer that you have not done your own, independent analyses of any relevant, publicly available astronomical data, but are considering doing so; is that correct?

  4. #64
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    I think that there are enough problems with the galactic disk and the stars moving radially and tangentially at the same speed, "spiralling" into the BH at the centre.
    So, I think we will let the "shooting out of the stars perpendicular to the disk" by a "change in how gravity works at high density" lie for the moment.
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  5. #65
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    Ok, thanks for the clarification.
    "...when you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes

  6. #66
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    Quote Originally Posted by john hunter View Post
    The Q&A questions was not the full extent, there was an extensive search on the internet and arXiv, which came up with the three papers linked in post 31, which showed a substantial radial velocity both towards and away from the centre of the galaxy. Here is part of post 31 again.

    "There is some evidence here:
    https://arxiv.org/abs/0803.1826 Fig 6 page 38 and Table 5 pg 59, especially column Vavg

    and https://arxiv.org/abs/1805.00275 Fig 1 page 2 and Fig 10 page 7

    and https://arxiv.org/abs/1006.0064 Fig 4.2.1 page 45, which shows stars moving in highly elliptical orbits. These three papers show that there are stars in the bulge moving in highly eccentric orbits with one star measured with radial velocity of over 400 km/s."

    Currently looking into RAVE and awaiting Tusenfem's or the moderators response to private emails, or of post 55.
    Thanks again.

    Two of those papers are, explicitly, about the “central parsec” of our own galaxy, and the third about the MW bulge, not the disk. None seem to have any relevance to the vast majority of stars in the disks of spiral galaxies.

    Do you have any observational data which is relevant to your ATM claims?

  7. #67
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    Quote Originally Posted by Jean Tate View Post
    Thanks again.

    Two of those papers are, explicitly, about the “central parsec” of our own galaxy, and the third about the MW bulge, not the disk. None seem to have any relevance to the vast majority of stars in the disks of spiral galaxies.

    Do you have any observational data which is relevant to your ATM claims?
    My bold. I'll second that.

    While I am at it, that graph in the second link in post 57 is not indicative of any discontinuity in the overall form of the galaxy. The author used different equations for different portions of the curve to empirically fit a smooth curve to an orbital velocity dataset without needing an ungodly huge number of terms. Remember, this is a multibody problem with no explicit analytical solution for the orbital elements. When the direction of the curvature changes several times it is my educated guess that a single equation for the whole range would have unacceptable squiggles between the fitted points. A set of cubic equations, each of which is used between two of the inflection (?) points, appears to be much more useful for the task at hand, which is interpolating between available data points.

  8. #68
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    Jean Tate and Hornblower. Post 31 Gave some evidence for a velocity dispersion in the bulge with a great many stars having velocity towards the CMO.

    Evidence for a universal flow of all stars in the disk towards the centre has not been found yet, although it's early days.

    However out of the billlions of stars that make a galaxy, the ATM thread requires approximately 1000 per year to enter the bulge from the disk. It could be that occasionally a star's orbit is changed by the spiral arms or other dense region causing a phenomenon of 'radial migration', which can occur both ways, inwards and outwards - it's going to take time to investigate whether there can be a net effect inwards - so maybe Jean Tate's advice of post 56 (of a pause) will be followed, if better evidence isn't found in a day or two.

    The theoretical advantages of the net inward flow are:
    A possible way for spiral patterns to emerge.
    A natural way to explain the matter distribution to give the flat rotation curves - i.e a constant inflow leads to a density rho proportional to 1/r^2 and m(r)/r=constant. Since most of the matter is dark matter, in the disk, the dark matter would also have a net inwards flow at constant speed.

    About the graph, second link post 57...Nature would have a way of smoothly linking the two straight lines in the previous graph. Only the points
    0 0
    1 8
    2 8
    3 8
    4 8 etc.. were put into the cubic-spline fitter, (try, from post 57 if you want), and a reasonable version of a rotation curve appeared. From this it strengthens the case that there are really just two regions. The flat one and the bulge of constant density, the rest of the shape seems to emerge as a requirement (according to the ATM model) of a constant inward flow meeting the constant density region.
    Last edited by john hunter; 2018-Jul-11 at 09:22 AM.
    "...when you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes

  9. #69
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    Quote Originally Posted by john hunter View Post
    However out of the billlions of stars that make a galaxy, the ATM thread requires approximately 1000 per year to enter the bulge from the disk.
    IF03: Please give or cite your calculation that requires ~1000 stars per year to enter the bulge from the disk

    IF02: Please give your prediction from your ATM idea for the galactocentric radial velocity of bulge stars with a galactic longitude of around 0 ("directly inwards" from the Sun).

  10. #70
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    Quote Originally Posted by Reality Check View Post
    IF03: Please give or cite your calculation that requires ~1000 stars per year to enter the bulge from the disk
    There was something on this in post 19. However...

    vt^2/r=Gm(r)/r^2

    m(r)/r=vt^2/G

    m(r) =(vt^2/G)*r

    In this ATM model, there is an inwards flow of at vr. In one second a 'shell' of matter would move a distance vr, which is of similar magnitude to vt, say 'v' approx. 230 km/s

    The amount of matter passing a radius r in one second is all the matter between radii r+v to r.

    (v^2/G)*(r+v)-(v^2/G)*(r)= (v^2/G)*(v) = (v^3/G) or more exactly vt^2*vr/G

    For an estimate 230000^3/6.67*10^-11=1.8*10^26 kg/s = 5.8*10^33kg/year. The Sun has mass 2*10^30kg, so it's 2900 solar masses per year.

    A lot of this flow could be dark matter, but it must flow along the disk, then from disk to bulge, then to CMO, then be ejected (perhaps in bursts), but all at the same rate, on average, to maintain a stable equilibrium.
    "...when you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes

  11. #71
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    Quote Originally Posted by john hunter View Post
    Jean Tate and Hornblower. Post 31 Gave some evidence for a velocity dispersion in the bulge with a great many stars having velocity towards the CMO.
    Could you elaborate on this please?

    As I read the “bulge” paper, there is evidence for a lot of stars having a component of their velocity “towards the CMO”; would you please explain how you concluded, from that paper, that the velocity is radial?

    Also, doesn’t that paper also provide evidence for a lot of stars having a velocity component away from the CMO?

    Evidence for a universal flow of all stars in the disk towards the centre has not been found yet, although it's early days.

    <snip>
    In the absence of such evidence, what is the point of this ATM thread?

  12. #72
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    A thousand stars per year falling through a given radius does not sound like much until we multiply it by, say, 100 million years. Then it adds up to the entire population of the disk. Virtually all the stars would have to be moving this way, and as has been pointed out, the type of motion john hunter is envisioning would be readily observable by the same means that we observe the transverse motion with respect to the galactic center. I would say that describing this idea as stillborn is an understatement.

  13. #73
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    Quote Originally Posted by john hunter View Post
    There was something on this in post 19. However...
    If I put 'v' approx. 0 km/s, I get 0 solar masses per year. If I put v ~ c, I get an enormous number of solar masses per year. We are back to how can we trust a number that you have presented no evidence for?

    vt^2/r=Gm(r)/r^2 is merely the mean orbital speed of a object in an essentially circular orbit around a mass of m(r). The shell theorem tells me that I can replace m(r) with m. In both cases, the radial velocity is zero. That implies that your ATM idea includes that Newtonian gravity is wrong. But that equation is derived from Newtonian gravity!
    Last edited by Reality Check; 2018-Jul-11 at 11:50 PM.

  14. #74
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    Reality Check: The tangential velocity component lets us estimate m(r)/r, which is v^2/G, but there can be a radial component too. If this is of similar magnitude to v (not 0 or c) then in-falling matter can trace out a spiral pattern...

    and Hornblower: The value of the radial component may vary from galaxy to galaxy, a great deal of matter would be passing through the centre and out again, but not necessarily destroyed, for the milky way it would take about 10^42kg divided by 10^26kg/s = 10^16s approx. 300 million years (This doesn't mean that the galaxy would disappear. Matter would be ejected from the CMO mostly perpendicular to the disc and some return mainly at the edges). If the radial component is on average 10% of the tangential, then it would be 10 times longer.

    Jean: The point of the first link in post 31 (https://arxiv.org/abs/0803.1826 Fig 6 page 38 and Table 5 pg 59, especially column Vavg), was to show that a substantial radial component exists in the bulge, previously to that (in the Q&A thread) there was no evidence found for any substantial radial component. Many stars have 200km/s for their radial component, similar to the tangential. there was also a 400km/s (radial).

    So instead of neat circular orbits, there are highly elliptical orbits - a chaotic situation.

    If their orbit was too close - they could be absorbed by the CMO. Also they could disturb each others orbits, which could occasionally cause one in an elliptical orbit to be diverted too close to the CMO and absorbed. Imagine there were 2000 stars in such orbits and gradually one by one they are absorbed by the CMO - later there might be 1000 in orbit and 1000 now forming part of the CMO. That's a net in-fall.

    As for 'universal flow' that's true. Not every star is always moving towards the centre (in this ATM thread). It's an average, net, in-fall. Averaged in terms of number of stars and also in time. You mentioned that you would like to see evidence for radial motion in the disc. There will be something posted on that soon.
    Last edited by john hunter; 2018-Jul-12 at 10:12 PM.
    "...when you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes

  15. #75
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    Quote Originally Posted by john hunter View Post
    Reality Check: The tangential velocity component lets us estimate m(r)/r, which is v^2/G, but there can be a radial component too....
    Yes: the tangential velocity component at r gives the mass inside r. But, the only radial component "estimate" you can make is that the radial component is between 0 and c. More realistically, guess that it is within an order of magnitude (or 2?) of the tangential velocity. Or look at the velocities of as many stars as possible in the galaxy and use that distribution. Or find values in the literature. Or find sources that give methods of deriving it from data such as the radial velocity (solar not galactic).

    It is still irrelevant that stars spiral in.
    Last edited by Reality Check; 2018-Jul-13 at 02:40 AM.

  16. #76
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    Here is probably the most up to date and best data available, for radial motion in the disc of the Milky Way, https://arxiv.org/abs/1804.09380 .
    What it shows is a complex situation, in which there are significant radial velocities both inwards and outwards. The paper has a lot of detail in it, but here are some relevant parts.

    -------------------------------------------------------------------------

    In the Abstract, just under Results: “The maps show the complexity and richness of the velocity field of the galactic disc. We observe streaming motions in all the components of the velocities…”

    Figure 10 page 11, top left diagram, shows VR, an interesting diagram which shows a vast blue region to the right of the sun (further radially outwards) moving inwards to the centre of the galaxy, at 15km/s (VR is the galactocentric radial velocity as described in the footnote at the bottom of page 4). Further radially inwards, the red region, there is a vast region moving radially outwards.

    Figure 12 page 13 shows median radial velocity against radius.
    To quote section 3.2. page 10
    “The median radial velocity has a U-shape, with a minimum at about 9 kpc. Around this minimum and within a broad layer below and above the mid-plane, the median radial velocity is negative, meaning that more stars move inwards than outwards. At a distance from the minimum of 1 to 2 kpc, the median radial velocity becomes positive, meaning that more stars move outwards than inwards.“ The data is probably more reliable at smaller distances from the sun, where the results show an inward flow.

    -----------------

    Top of page 16 “Grand et al. (2016) used cosmological simulations to study the large-scale motions induced by the spiral arms in a Milky Way-like galaxy. The simulation shows radially outwards and azimuthally backwards motions on the trailing edge of the arms, while on the leading edge, the effect is reversed: the streaming motion is oriented inwards and forwards.

    There are also Fig 19, page 16 and Figs C1, C2 pages 29/30.
    ----------------

    The dispersion is large for VR, a larger dispersion than for the other velocity components. Up to 70km/s for sigma(VR), Fig 16 page 15. And Figs C8/9 pages 36 and 37

    In Conclusions page 21
    "The picture of the Milky Way disc kinematics drawn by Gaia DR2 is both rich and complex. Streaming motions are observed in all three velocity components…We find that stars clearly appear to be organised in kinematic arches… Gaia DR2 is now available to the astronomical community… We can expect this great wealth of information to trigger an intense activity in the galactic community in the years to come."

    ---------------------------------------------------------------

    It’s probably not going to be possible to quickly find conclusive evidence for or against a net radial inwards motion, but the paper shows that such a net inwards motion is a serious possibility, especially given that vast quantities of matter are periodically ejected, from galaxies, perpendicular to the disc.
    Last edited by john hunter; 2018-Jul-13 at 10:05 AM.
    "...when you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes

  17. #77
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    I see nothing in the paper linked in post 76 from which I would infer a long term, systematic spiraling in of stars into the center of the galaxy. The authors note that the galaxy in not in equilibrium, which is normal after recent mergers with various small galaxies. For disk stars I would expect a present day net inflow, if any, to evolve into a net outflow as the respective stars round the periapsides of their eccentric orbits and start moving out again. Stars that remain intact in extremely close approaches to the central black hole will just whip around and go back out in the same orbit, like an Oort cloud comet flying by the Sun. The stuff that squirts out along the polar axis is gas that came into the accretion disk and was deflected by fluid dynamics that would not apply to intact stars.

    This ATMer appears to be cherry-picking words and phrased from published papers upon envisioning them as somehow concurring with his ATM idea.

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    H
    Last edited by Dave Lee; 2018-Jul-13 at 03:45 PM. Reason: error

  19. #79
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    Hello John

    Your key message is valid.
    However, did you also consider an option for stars to drift outwards instead of inwards?
    Last edited by Dave Lee; 2018-Jul-13 at 04:54 PM.

  20. #80
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    Quote Originally Posted by john hunter View Post
    <snip>

    It’s probably not going to be possible to quickly find conclusive evidence for or against a net radial inwards motion, but the paper shows that such a net inwards motion is a serious possibility,
    I think you and I must be reading different papers (YMMV of course). I cannot see how such a thing is a “serious” possibility.

    especially given that vast quantities of matter are periodically ejected, from galaxies, perpendicular to the disc.
    Huh?

    Do you have solid evidence for this? Perhaps start with quantifying “vast quantities”, and “galaxies”. Thanks in advance.

  21. #81
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    Quote Originally Posted by john hunter View Post
    Here is probably the most up to date and best data available, for radial motion in the disc of the Milky Way, https://arxiv.org/abs/1804.09380 ...
    The real question is:
    IF04: How closely do the galactocentric velocities in this paper match your ATM idea predictions, john hunter?

  22. #82
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    A few weeks ago, evidence was being wondered about for any radial motion at all, either in the bulge or disc of a galaxy.

    In post 31 evidence was given for substantial radial motion in the Milky Way bulge.
    The paper in post 76 shows that there are regions with substantial radial motions of matter in the Milky Way disc.

    The situation is complex and chaotic with streaming motions of matter both inwards towards and outwards from the galactic centre.
    A model with near circular orbits would not match these observations. A model with a substantial radial inflow could.

    Nasa’s Fermi telescope found these ‘Fermi bubbles’. Immense Lobes seemingly formed by matter ejected perpendicular to the Milky Way disc. https://www.nasa.gov/mission_pages/G...structure.html

    This paper https://arxiv.org/abs/1612.01578
    puts the visible mass of the bubbles in excess of 2x10^6 solar masses, with a minimum outflow rate of 0.2 solar masses per year. There is 20 times more dark matter in the disc than visible, and the paper used a low ejection speed of 1000km/s. Jets commonly occur in galaxies with velocities near the speed of light. Streaming radial motion outwards in the disc has also been found (link in post 76) , so there are a few reasons to think that this minimum is set low and will be increased as our knowledge/observations improve.

    There is evidence of substantial outflows in the form of Jets and AGNs from other galaxies too, will be posted later.
    Last edited by john hunter; Today at 11:36 AM.
    "...when you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes

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