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Objects turning into a black hole near the speed of light?

  1. Apr 26, 2005 #1
    The Theory of Relativity proposes equivalence between mass and energy. Well... since they are "equal", when mass disturbes the spacetime which causes a forcefield that we call gravity, energy should have the same effect on spacetime. Putting a huge amount of mass in a very little place in space, we have a black hole. After this little explanation my question ;):

    Does any Kind of energy have the same effect? Thus heating up some gas to a 10^xxxxxxxxxxxx Temperatur would -in the end, theoretically- cause a black hole beeing created? Another example would be a gigantic magnetic field. Which causes such a large density of energy in a certain place that spacetime would collapse? Now my last and maybe most controverse example:
    Is it possible to accelerate an object on such a high speed that his kinetic energy (from the frame of reference of the observer) would cause the object to let spacetime around it collapse into a black hole?
    I thought maybe this effect would not appear since time slows time in the frame ofthe accelerated object. Thus making its spacetime more "spread out". And working against the black-hole thing.
    And last but not least: if you place the observer in the object which is Now flying veryvery close to the speed of light. wouldn't everything else which hasn't been accelerated look like a black hole? I'm just wondering and would love to get some answers of people who really know this stuff.
  2. jcsd
  3. Apr 26, 2005 #2
  4. Apr 26, 2005 #3


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    This question is addressed in the Usenet physics FAQ, in the section If you go too fast do you become a black hole?:
  5. Apr 27, 2005 #4


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    Take a look at the sci.physics.faq on the topic at the following link:

    If I go too fast, do I turn into a black hole?

    [add] Oh, I see Jesse beat me to it.

    The answer to this part of your question is that you do not turn into a black hole if you go too fast.

    I think some of your other ideas could work in theory though (they probably won't actually happen, they are more in the line of thought experiments). The formulas you'll see for the critical density of a black hole assume that one is in the center of mass frame of the system - changing the velocity has no effect on whether or not an object becomes a black hole.

    Temperature is a form of energy, so if you could somehow heat an object up hot enough AND keep it confined to a small areaa (a rather difficult job, because it will tend to expand), you could probably in principle form a black hole.

    Even in the center of mass frame, the condtions for forming a black hole aren't definitely known, but there is a conjecture, known as the "hoop conjecture", which basically says that an object of mass M has to have a circumference of less than 4*pi*GM/c^2 in all directions in order to form a black hole. See for instance

  6. Apr 27, 2005 #5
    Wait, are you people saying that if object posseses so much relavistic mass in one area of space, a black hole will open? This is BS, I have aksed that same questio here before and somebody told me I didnt know what I was talking about, and that it does NOTwork that way.

    I don't know what to belive anymore. I though physicsforums was well educated, now it seems that people just say things to seem kewl, or they dont really know what they are talking about.
  7. Apr 27, 2005 #6
    Whomever told you that sure didn't know what they were talking about. Its well known that a star can collapse to form a blackhole. Don't think of it as something "opening" though. That way of phrasing it gives me the willies!!! :bugeye:

  8. Apr 27, 2005 #7
    Well, that situation was reffering to relavistic mass, not rest mass. :yuck:
  9. Apr 27, 2005 #8
    That doesn't tell me why he thinks the equivalence principle is not consistent with the scalar theory. Brans and Dicke didn't create a theory without it that's for sure (and for the reasons I mentioned). Remember that the time component of the energy-momentum tensor is the mass of the system. It remains as such even when the system is composed of photons with random directions etc.

  10. Apr 27, 2005 #9


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    No, everyone who has answered yeus' question so far said the exact opposite, that an increase in relativistic mass without an increase in rest mass will not cause a black hole to form. Read the responses again.
  11. Apr 27, 2005 #10


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    eNathan was talking only about an increase in relativistic mass due to increased velocity causing a black hole to form, without any change in mass or density in the object's rest frame--you yourself agreed this couldn't happen in your original response to yeus.
  12. Apr 27, 2005 #11
    It appeared to me that in his follow up to me that he was now referring to the rest frame - I have to admit that it was a bit unclear and I should have asked for clarity. I took his comment "in one area of space" to be quite general and as such apply to the rest frame as well, as in pack the matter into smaller region of space and you get a black hole.

    To be honest, this is getting confusing to me.

  13. Apr 27, 2005 #12
    In Gravitation, by MTW, one of the more whimsical results is a theoretical limit on horspower, about 10^54 h.p., after which point black hole formation is unavoidable.
  14. Apr 27, 2005 #13
    Imagine a massive object bouncing around inside a perfect box (ie perfectly elastic, and as rigid as relativity allows).

    As the speed of the object increases inside the box, does the external gravity field of the box increase?
  15. Apr 27, 2005 #14


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    Why would the speed of the object increase? Wouldn't that violate conservation of momentum?
  16. Apr 27, 2005 #15
    Good point!

    Let me think...

    Let's say we have two identical objects in two identical boxes. The object in one box is bouncing around much faster than the object in the other box. Does the box with the fast object have more gravity?
  17. Apr 27, 2005 #16


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    I'm not sure...on the one hand, between collisions you can always find a frame where the object in the second box is moving slower, but maybe the constant changes in direction after each collision would break the symmetry...pmb_phy said that increasing temperature could cause a black hole to form, and increasing the temperature of a box filled with gas molecules just means increasing the average speed of all the molecules bouncing around between walls. Maybe someone who understands GR better can give a more definite answer.
  18. Apr 28, 2005 #17
    I'm trying to approach it using SR and Newtonian gravity by considering conservation of momentum as the box falls toward another massive object.... but I'm a bit too lazy to follow it through rigorously.

    My unreliable intuition at the moment is that the fast moving object-in-box results in a high average gravity field... and if I knew any GR I might think about the object-box collisions perhaps producing gravity waves with the same result?
  19. Apr 28, 2005 #18
    Yes. That is correct.
    These are not too different things. They are identically the same thing. Increasing the average speed of particles in a box is synonymous with increasing the temperature of the gas and thus increasing the active gravitational mass of the gas. Increase if far enough and the result will be a black hole (theoritically possible. Too difficult in practice of course.

    Note that the gravitational field of a single particle will change with the change of the speed of the particle. However that does not mean a black hole will form.

  20. Apr 28, 2005 #19
    Can I please just get a straight answer here.

    1. Does relavistic mass create gravity?

    2. Is it as easy to calculate as just plugging in the relavistic mass variable into the universal gravity equation?
  21. Apr 28, 2005 #20


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    No to both, at least not if you're talking about increasing an object's velocity in a uniform way (increasing the velocity of all the particles in a single direction). As long as the object doesn't look any different in its own rest frame, it will be no more likely to form a black hole.
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