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Thread: Frame dragging and galactic rotation

  1. #1
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    Frame dragging and galactic rotation

    Could the anomaly of the velocity of galactic rotation be explained by frame dragging, that is, that the velocity of rotation measured here does not take into account that the space in which the galaxy is embedded is itself rotating, due perhaps to frame dragging?

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    Welcome to Cosmoquest! Good question, but I think that frame-dragging is something that happens at very high relative velocities, not at the kinds of velocities that stars orbit around a galaxy.
    As above, so below

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    All most all of the rotation question was answered when they were able to use gravitation bending of light to extrapolate the dark matter halo's that surround the galaxies. The rest I think can be explained by the more recent discovery of the large scale magnetic forces that seem to flow along the arms of the galaxies, which leads to increased star formation and some weak magnetic dragging.

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    Quote Originally Posted by dgavin View Post
    All most all of the rotation question was answered when they were able to use gravitation bending of light to extrapolate the dark matter halo's that surround the galaxies. The rest I think can be explained by the more recent discovery of the large scale magnetic forces that seem to flow along the arms of the galaxies, which leads to increased star formation and some weak magnetic dragging.
    I would be flabbergasted if a magnetic field that is only recently discovered could perturb an orbiting star measurably from what its purely gravitational motion would be.

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    We've measured frame dragging effects around Earth (specifically the Lense–Thirring effect) - and they are small enough that we can rule them out as being responsible for galactic rotation curves. Essentially for them to be responsible they'd have to behave very differently on galactic scales than they do locally.

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    Quote Originally Posted by Shaula View Post
    We've measured frame dragging effects around Earth (specifically the Lense–Thirring effect) - and they are small enough that we can rule them out as being responsible for galactic rotation curves. Essentially for them to be responsible they'd have to behave very differently on galactic scales than they do locally.
    I just had the same question and I found this article:
    http://news.mit.edu/1997/blackholes

    But I am not sure about the range the frame dragging applies.

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    Quote Originally Posted by dgavin View Post
    All most all of the rotation question was answered when they were able to use gravitation bending of light to extrapolate the dark matter halo's that surround the galaxies.
    In the context of the question, I'd say your answer is a tautology.

    They extrapolate what density and distribution of dark matter would result in the observed effect - if DM were the culprit, but it doesn't in-and-of-itself demonstrate that DM is the only solution that fits the observations.
    Last edited by DaveC426913; 2018-Oct-09 at 12:37 AM.

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    Is this paper of help in this discussion? Apologies if not, but it looked relevant.


    https://arxiv.org/abs/1810.04445

    Shedding light on the Milky Way rotation curve with Gaia DR2

    Mariateresa Crosta, Marco Giammaria, Mario G. Lattanzi, Eloisa Poggio (Submitted on 10 Oct 2018 (v1), last revised 16 Oct 2018 (this version, v2))

    Flat rotation curves in disk galaxies represent the main evidence for large amounts of surrounding "dark" matter. Despite of the difficulty in identifying the dark matter contribution to the total mass density in our Galaxy, stellar kinematics, as tracer of gravitational potential, is the most reliable observable for gauging different matter components. Very recently, the Gaia mission has provided such data with unprecedented accuracy and consistency over a range of 11 kpc in Galactocentric distances. By fitting both a "classical" (which includes a DM halo) and a relativistic (as derived form a specialized solution of Einstein's field equation) rotational curves to the Gaia-derived circular velocities of a homogenous sample of disk stars (the largest sample of its kind ever), we put forth the Ansatz that a stationary and axisymmetric galaxy-scale metric could "fill the gap" in a baryons-only Milky Way, suggestive of dragged star orbits along the background geometry generated by a rotating inner bulge. Therefore, in the context of Local Cosmology, our findings point to a Galaxy phase-space as the exterior gravitational field of a Kerr-like source without the need of extra-matter.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
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    Just so everyone is aware, pedoggett started this thread two years ago and hasn't been back since. And Q&A threads aren't for general, long-term discussions. I'm moving this thread to Astronomy, so you may all carry on.
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  10. #10
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    Quote Originally Posted by DaveC426913 View Post
    Quote Originally Posted by dgavin View Post
    All most all of the rotation question was answered when they were able to use gravitation bending of light to extrapolate the dark matter halo's that surround the galaxies.
    In the context of the question, I'd say your answer is a tautology.
    No, it's not.
    They extrapolate what density and distribution of dark matter would result in the observed effect - if DM were the culprit, but it doesn't in-and-of-itself demonstrate that DM is the only solution that fits the observations.
    I read dgavin's post again--those are two separate calculations of the mass of the dark matter. The first is the mass necessary to produce the galaxy rotation curve, and the second is the mass necessary to produce the bending of light. If those two calculations agree, it would be pretty coincidental if there weren't an actual effect.

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    Quote Originally Posted by philippeb8 View Post
    ....But I am not sure about the range the frame dragging applies.
    That's the thing. I haven't done the GR math, but it seems to only apply significantly very close to the surface of a very dense spinning object, and the effect drops off - apparently exponentially - with distance from that surface. (And it seems to be a very large exponent.)
    Everyone is entitled to his own opinion, but not his own facts.

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