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  1. #1
    Jeff Bucove's Avatar
    Jeff Bucove Guest

    Default [Fwd: Dark Matter: black hole frame drag?]





    -------- Original Message --------
    Subject: Dark Matter: black hole frame drag?
    Date: Fri, 26 Nov 2004 17:31:50 -0800
    From: Jeff Bucove <bucove@telus.net>
    Newsgroups: alt.astronomy



    I have always had a problem with the dark matter thing. As an
    explanation for too much "apparent" gravitational force at galactic
    scales it sucks.

    I have always been sure that there is an observational problem
    involving unknown forces at great distance or other as yet to be
    discovered phenomena.

    I have recently learned through public media that the spinning super
    sized black hole at the center of our Galaxy has an angular velocity at
    the event horizon of 1/3 the speed of light, or C/3.

    I am posting to ask authoritative astronomers this question:

    Could the relativistic frame drag of an object this massive spinning at
    this speed generate enough spiral warpage of space-time to account for
    the observed clustering of matter on galactic scales?

    ....jeffery




  2. #2
    Double-A's Avatar
    Double-A Guest

    Default [Fwd: Dark Matter: black hole frame drag?]

    Jeff Bucove <bucove@telus.net> wrote in message news:<3VQpd.208951$9b.189046@edtnps84>...

    An interesting consideration.

    I don't know about the clustering, but the frame dragging influence
    from a massive black hole might affect the galaxy such that the
    galactic spin might appear to be faster than what gravity could
    account for, if the rotation of the black hole were in the same
    direction as the galactic rotation. And isn't this exactly what is
    being observed?

    The only question would be how far the influence of the black hole's
    frame dragging would extend.

    Arlyn

  3. #3
    Jumpin Jeff's Avatar
    Jumpin Jeff Guest

    Default [Fwd: Dark Matter: black hole frame drag?]

    Double-A wrote:

    Well yeah, it is true that (influence distance) is the primary of two
    inherent questions in my querey, the other is the scale of the power of
    the frame drag effect, i.e. if the above is true: how much faster
    is/would be the observerved galactic spin than is the "real galactic
    orbital speed" that is, from a space-time frame fixed reference that
    subtracts the galactic core's frame drag quotient.

    (ouch this stuff bends my head..

    http://einstein.stanford.edu/
    The Gravity Probe B mission is current and determining some of this
    stuff, I was just wondering if we know the magnitudes well enough from
    theory to eliminate the framework of my question.



  4. #4
    Double-A's Avatar
    Double-A Guest

    Default [Fwd: Dark Matter: black hole frame drag?]

    Double-A wrote:
    at
    at
    for

    Well yeah, it is true that (influence distance) is the primary of two
    inherent questions in my querey, the other is the scale of the power
    of
    the frame drag effect, i.e. if the above is true: how much faster
    is/would be the observerved galactic spin than is the "real galactic
    orbital speed" that is, from a space-time frame fixed reference that
    subtracts the galactic core's frame drag quotient.

    (ouch this stuff bends my head..

    http://einstein.stanford.edu/
    The Gravity Probe B mission is current and determining some of this
    stuff, I was just wondering if we know the magnitudes well enough from
    theory to eliminate the framework of my question.


    Double-A writes:

    You should try posting your question to sci.physics.relativity.

    There are several prominent astrophysicists who peruse that group, and
    they may be able to give you a quantitative answer to your question.

    Double-A

  5. #5
    Mike Williams's Avatar
    Mike Williams Guest

    Default [Fwd: Dark Matter: black hole frame drag?]

    Wasn't it Double-A who wrote:


    What is being observed is that the rate of decrease of rotation speed as
    you move out from the centre of the galaxy is less than one would expect
    if most of the mass is concentrated at the core.

    If ALL the mass were concentrated at the core, then the periods of stars
    in the galaxy would obey the same rules as planets orbiting the Sun,
    where the square of the period is proportional to the cube of the
    radius. The mass of a galaxy isn't all concentrated at the core, and
    this changes things so that the orbits in the outer regions are faster
    than that. By observing how fast the outer orbits are compared to the
    inner orbits we can determine that most of the mass of the galaxy is in
    the galactic halo, where there are few stars and few obvious places for
    that mass to reside.

    I don't know much about frame dragging, but I suspect that it would tend
    to affect the core regions far more than objects at the edge of the
    galaxy. This might possibly fit what's going on if the black hole is
    more massive than we would otherwise think, and rotates in the opposite
    direction from the rest of the galaxy. Thus the speed of stars in the
    halo would be mainly driven by gravity effects, but the speed of stars
    near the core would be reduced. However, it seems very unlikely to me
    that so many observed galaxies would happen to have counterrotating
    black holes, since infalling stars would tend to spin up the black hole
    so that it rotated in the same direction as the galaxy.

    --
    Mike Williams
    Gentleman of Leisure

 

 

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