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Recoil may eject black holes from a galaxy

  1. Feb 4, 2004 #1

    marcus

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    I hadnt heard of GW recoil imparting velocity to a black hole.
    http://www.arxiv.org/astro-ph/0402056

    "How Black Holes Get Their Kicks..."

    It's an article by three people, from Cornell, MIT, and Chicago.

    When two black holes spiral in and merge, linear momentum is carried off asymmetrically by a burst of gravitational waves at the end

    unless the two holes have equal mass (which one wouldnt expect them to have)

    and this one-sided burst of GW produces a "recoil" which can give
    the resulting black hole a velocity big enough to take it out
    of the galaxy or globular cluster it belongs to

    would not have expected this, their explanation of it is interesting

    the effect was first predicted in 1982
     
  2. jcsd
  3. Feb 4, 2004 #2
    I have heard of a simulacrum of this idea, which is described in the novel Moonseed, by Stephen Baxter. Two celestial bodies, Venus and, er, I shall not spoil it for you, blow up from the effect of nano-machines or something. The after-effects of the cataclysmic destructions leave black hole "boosters". The black holes would be moving at the speed of light, and sweep up anything in their paths. At the end, pioneers use the black holes to travel approximately 300,000 kilometers per second and colonize the galaxy.

    Now that would certainly make a trip to the Andromeda galaxy easier, but at such a tremendous price! (Again, I refrain in revealing of too much data. Read the book.)
     
  4. Feb 4, 2004 #3

    marcus

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    :smile:
    in this article the recoilspeeds produced by the holes falling together are only a few hundred kilometers per second.
    it's a conventional journal article by conventional astrophysicists

    but I have to confess that the conclusion seems bizarre to me

    do you understand their explanation

    it is peculiar because the center of mass of the two holes
    starts out basically standing still

    then they merge and suddenly the combined hole is moving off to the left at several hundred km/second. what happened to Conservation of
    Momentum?

    where did all the momentum come from?
    what did they send moving off to the right so it would have equal and opposite momentum? what takes the place of rocket exhaust?

    the recoil momentum comes from sending a burst of gravitational waves off to the right.
    but it has to be an extremely powerful pulse to carry the same momentum as stellar-mass black holes moving hundreds of km/sec.

    if your scifi author figured out how to make that happen, more power (and momentum) to him
     
    Last edited: Feb 4, 2004
  5. Feb 5, 2004 #4
    (Apparently) The momentum for the black holes came from some GUT/Dimension-Unfolding power. It goes pretty deep in the book, but the info I have is shallow. I'd suggest reading Moonseed, as the black hole booster theory occurs many times in the book.
     
  6. Feb 6, 2004 #5

    wolram

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  7. Feb 6, 2004 #6

    wolram

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  8. Feb 6, 2004 #7

    marcus

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    I looked at "Dynamics of BH Nuclei" by David Merritt and it covers a lot of ground, with plenty of pictures. Thanks for the link.

    Yes. There could be hundreds of stellarmass BHs zooming around.

    the momentum comes during the final plunge together. as some of these people explain.

    they spiral around each other radiating off energy with GW and then they go faster and faster and radiate off a huge burst and abruptly fall in together. And at that point it is not symmetric (because one is more massive, unless they just happen to be the same mass) and in that plunge ONE of them accelerates more and GW is radiated in a lopsided way

    so that carries momentum off in one direction and gives a recoil kick

    so the merged black hole is flying in the opposite direction with enough speed so it could leave a small galaxy or a globular cluster

    this is extremely strange to me but the people who are expounding it seem to be reasonable well-qualified people.
    so I have to accept the idea that in the universe there are black holes zooming around which are big enough to eat the earth for breakfast. it is not a comforting thought

     
  9. Feb 6, 2004 #8

    wolram

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    none of this makes me happy, it just seems totally wrong,
    but it seems there is some observational evidence to re enforce
    the theory, could there be some error in the data?
     
    Last edited: Feb 6, 2004
  10. Feb 6, 2004 #9

    wolram

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    i have had a little time to think about this and in my
    ever skeptical way have decided its a load of old
    cods wallop sorry if i am not scientific with my
    thoughts.
     
  11. Feb 7, 2004 #10

    wolram

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    http://arxiv.org/PS_cache/astro-ph/pdf/0402/0402057.pdf


    ABSTRACT
    Coalescing binary black holes experience an impulsive kick due to anisotropic emission of gravitational waves.
    We discuss the dynamical consequences of the recoil accompanying massive black hole mergers. Recoil velocities
    are sufficient to eject most coalescing black holes from dwarf galaxies and globular clusters, which may
    explain the apparent absence of massive black holes in these systems.
    ----------------------------------------------------------------------
    this is the best explanatory paper i can find and is worth
    reading its only a couple of pages.
     
  12. Feb 7, 2004 #11

    marcus

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    by a nice coincidence, they begin by referring to the paper I linked to at the start of the thread. It is by 3 of the authors who wrote this one.

    --------
    1. Kick Amplitude
    In a companion paper (Favata, Hughes & Holz 2004; hereafter
    Paper I), the amplitude of the recoil velocity experienced
    by a binary black hole (BH) due to anisotropic emission
    of gravitational radiation during coalescence is computed.
    --------

    the "companion paper" by Favata, Hughes, Holz
    http://arxiv.org/PS_cache/astro-ph/pdf/0402/0402057.pdf
    has a reasonably clear description of how the
    anisotropy ("lopsidedness") of the radiation arises,
    mostly during the final plunge
     
  13. Feb 7, 2004 #12

    Stingray

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    Why?

    Everything they talk about is normal physics. That the effect exists isn't hard to guess. Gravitational radiation can carry away linear momentum, so its reasonable that a strongly radiating asymmetric system would do this. The contribution of this paper is more about showing exactly how large the effect is.
     
  14. Feb 8, 2004 #13

    wolram

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    quote, stingray.

    Everything they talk about is normal physics. That the effect exists isn't hard to guess. Gravitational radiation can carry away linear momentum, so its reasonable that a strongly radiating asymmetric system would do this. The contribution of this paper is more about showing exactly how large the effect is.
    -------------------------------------------------------------------
    i know my comment is not justified, but have you ever
    thought our grasp on reality is slipping, ok these things are
    possible given our present theories are correct, but
    i have doubts, if we take everything we are told for granted
    then our universe is ever more strange and hostile to life.
    the next decade is probably going to be the turning point in our
    theories of gravity and how our universe works, but i will
    remain skeptical until we have proof of what gravity is,
    may be my view is unscientific and i am in a minority but this
    doesn't worry me, when gravitational radiation is detected i
    fall in line.
     
  15. Feb 8, 2004 #14

    wolram

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    the second of these two articles demonstrates that not everything
    is black or white, a slip with the numbers gave birth to a BH
    now they are not sure.
    ----------------------------------------------------------------------

    http://www.space.com/scienceastronomy/astronomy/blackhole_010913.html

    Conducting a bit of astronomical archaeology, researchers have dug up 43-year-old photographic evidence of an ancient black hole and used the information to learn that the object has been wandering at high speed on an odd, looping path through the Milky Way Galaxy for 7 billion years.
    ----------------------------------------------------------------------------
    20 jan 2003.

    http://www.space.com/scienceastronomy/blackhole_trick_030120.html

    It turns out there may not even be a black hole in the star cluster, called M15, a separate team of astronomers now says. Instead, a more plausible explanation is that the central region of M15 is a mass cosmic grave
     
  16. Feb 8, 2004 #15

    Stingray

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    Ok, fair enough. Even if GR is wrong though, I doubt that the alternative would lack gravitational waves. Almost any theory you try to write down would have them (of course the numerical predictions would be different in every case) unless you go with action-at-a-distance type models.

    I also don't see this as being very hostile to life. It wouldn't be a very common process, and it would still be very unlikely that any wandering object would get near enough to do any damage. The threat of a nearby supernova is probably much worse.
     
  17. Feb 8, 2004 #16

    wolram

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    quote stingray.

    Ok, fair enough. Even if GR is wrong though, I doubt that the alternative would lack gravitational waves. Almost any theory you try to write down would have them (of course the numerical predictions would be different in every case) unless you go with action-at-a-distance type models.
    -------------------------------------------------------------------
    action at a distance sounds implausible but i wouldn't
    rule out the possibility of some kind of entanglement
    I'm not exactly sure what i mean by this an dont want
    to join the crackpot brigade, i can only wait for
    evidence of gravitational radiation, but what if
    it is not found?
     
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