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Thread: centrifugal force

  1. #1
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    centrifugal force

    if a galaxy's spin started to accelerate what would be the apparent change from the observations of say a star/planet on one of the outer arms?

    I would assume that the galaxies in front and in back of the galaxy ( in the direction of the spin ) would get further away from it ...

    Would ones that were further out from the center and further in from the center also get further away?

  2. #2
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    Galaxies don't spin. The stars orbit.

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    If we could magically accelerate all objects in the galaxy prograde in unison, they would fly apart from each other and from the center. If we increase their velocities enough, they could escape.

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    Quote Originally Posted by NEOWatcher View Post
    Galaxies don't spin. The stars orbit.
    OK ... but what if the stars orbited faster ?

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    Quote Originally Posted by tommac View Post
    OK ... but what if the stars orbited faster ?
    Hornblower said it well, things just get farther apart.
    At least at first. If they don't reach escape velocity, they would go more elliptical. At apoapsis, they would start to head back to periapsis appearing to collapse, then it all starts again. (It's a basic concept of orbits)
    The interaction of individual stars gets different because of local influences.

    The bottom line is, you can't look at a galactic movement as a single object.

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    Would the amount of mass in the galaxy or the spin of the SMBH in the center speed up the average orbital speed of the galaxy?

    Quote Originally Posted by Hornblower View Post
    If we could magically accelerate all objects in the galaxy prograde in unison, they would fly apart from each other and from the center. If we increase their velocities enough, they could escape.

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    Why would the mass in the galaxy cause it to speed up? That would imply that the orbits of stars in galaxies gradually get faster and faster; which I don't think they do (otherwise they would rip themselves apart).

    The rotation of the black hole would have some local effects on accreting matter due to frame dragging but would be negligible elsewhere.

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    How local is local?

    Quote Originally Posted by Strange View Post
    Why would the mass in the galaxy cause it to speed up? That would imply that the orbits of stars in galaxies gradually get faster and faster; which I don't think they do (otherwise they would rip themselves apart).

    The rotation of the black hole would have some local effects on accreting matter due to frame dragging but would be negligible elsewhere.

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    Quote Originally Posted by tommac View Post
    Would the amount of mass in the galaxy or the spin of the SMBH in the center speed up the average orbital speed of the galaxy?
    If the mass of a galaxy suddenly increased for some odd reason -- two extragalactic SMBHs smashing into one another from opposite directions at the galactic c.g. -- then I assume the orbital velocities (galactic rotation) of the galaxy would increase during contraction.
    We know time flies, we just can't see its wings.

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    Quote Originally Posted by George View Post
    If the mass of a galaxy suddenly increased for some odd reason -- two extragalactic SMBHs smashing into one another from opposite directions at the galactic c.g. -- then I assume the orbital velocities (galactic rotation) of the galaxy would increase during contraction.
    Remembering that galaxy kinematics are dominated by dark matter and not SMBH's, and discounting all that flinging of stellar matter all over the place, I doubt that doubling or tripling the SMBH mass would make a lot of difference in many galaxies.

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    Quote Originally Posted by loglo View Post
    Remembering that galaxy kinematics are dominated by dark matter and not SMBH's, and discounting all that flinging of stellar matter all over the place, I doubt that doubling or tripling the SMBH mass would make a lot of difference in many galaxies.
    That's a good point considering the mass of the Dark Matter halo. There would be some local changes, but not on the whole without merging with another blob of dark matter, which I assume would require a galactic merger.
    We know time flies, we just can't see its wings.

  12. #12
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    Quote Originally Posted by George View Post
    That's a good point considering the mass of the Dark Matter halo. There would be some local changes, but not on the whole without merging with another blob of dark matter, which I assume would require a galactic merger.
    Yeah, we seem to have swallowed a few dwarf galaxies without any large scale disruption so one with a bit of meat on its bones would be required.

  13. #13
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    Quote Originally Posted by tommac View Post
    How local is local?
    For a super massive black hole...much less then then the size of our solar system
    like time dilation its effect drop off very quickly from the event horizon

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