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Are you sure that objects which moves enought fast are not black holes?

  1. Jul 3, 2006 #1
    In order that any mass creates a gravitational field, if those objects do not become black holes, this means that relativistic mass does not create a grav field.

    How can a mass increasing not produce a deeper space warp? That is the mass does not increase with speed?
    Apologies my english.
  2. jcsd
  3. Jul 3, 2006 #2


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    See the sci.physics.faq http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_fast.html" [Broken]

    Whether an object is a black hole or not is a global property of the object. Therfore if an object is not a black hole in it's rest frame, it is not not a black hole if you whiz by it at a high velocity.

    The gravitational field of an object can change when its velocity changes. This can most easily be seen by means of the tidal force.

    If you move at "right angles" to an object, the tidal force you experience will be greater than if you were standing still.

    Interestingly enough, however, if you move directly towards or away from a massive object, the tidal force you experience will not change (it will be the same as if you were not moving).

    You can find the later fact in MTW's "Gravitation" (page numbers on request).

    This demonstrates that velocity can change "gravity". It also helps illustrate how the gravity from a moving object is not symmetrical. It is stronger "to the sides" than it is in front or in back. This is similar in general behavior (though not in exact detail) to how the electric field from an electric charge acts.

    What's important as far as an object being a black hole or not is whether or not light can escape from it. That does not change when the velocities object changes.
    Last edited by a moderator: May 2, 2017
  4. Jul 4, 2006 #3
    Hmmmm, is that correct?
    Does not something happen to the visibility of particles leaving or entering an object during a change in velocity?
  5. Jul 4, 2006 #4


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    Consider the rest frame of the object. Light leaves it and escapes to infinty.

    Now consider the object in a moving frame. Light abberrates, but it still escapes to infinity.

    For an object to be a black hole, light must be trapped by the object.
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