Black Holes - Where does all the matter go

  1. Okay,

    Lets take a black hole. time, matter - everything is drawn in by the massive gravitational pull of this singularity. The laws of science break down as there is a point in space where there is nothing.

    I hope that is accurate -if not please correct me.

    So, we have this drain of everything situation building up. now this is where I get a little hazy in my understanding. What happens to everything that is drawn in -the time, the matter, (the anti-matter?)?

    I have several ideas and was wondering if you could offer some thoughts.


    • Does it simply build up and the singularity get bigger - I do not believe this is the case, as otherwise black holes would simply grow exponentially and 'consume' the universe.

    • Does the matter become highly concentrated and more dense, tending towards an infinite density? however once more this would simply cause the universe to collapse into an ever growing black hole.

    • Does the matter get 'moved' somewhere?

    • Or simply what does happen?!

    Any thoughts would be well recieved.

    Regards,

    Ben

    (and do white holes exist - where the concept of time relative to the creation of a black hole is reversed?)
     
  2. jcsd
  3. the stuff sucked stays there
    making the BH bigger in mass
    point size is more a math idea then a proven fact
    the event horizen does get bigger as mass is gained

    white holes are as yet unfound and would be hard to hide
    so may not be
     
  4. Okay so: an increase in size, may give three results.

    A decrease in denity, an increase in density or no change in density.

    If it were the last two the black hole would continue to grow and 'consume' everything in the universe. Is this what you are suggesting?

    In the first instance I am not sure what would happen!!

    Why not white hole = big bang?


    Regards,

    Ben
     
  5. chroot

    chroot 10,426
    Staff Emeritus
    Science Advisor
    Gold Member

    According to the classical theory of black holes -- that governed by general relativity alone -- the singularity is already a point of infinite density. You can continue adding mass for it forever, and it will never grow in size; it will always be of infinite density.

    If everything in the universe were to fall into a black hole, then, indeed, the black hole would have 'consumed' the entire universe. Luckily, the majority of the matter in the universe is not in a trajectory that will lead it to collide with a black hole anytime soon, if ever. Remember that, from a distance, a black hole acts no different from any other object with equivalent mass. They're not like "vacuum cleaners," a common misconception.

    - Warren
     
  6. Thank you for your reply, and i do not treat them as 'vacuum cleaners'.

    But I do consider them i this way. If they have infinite mass, their gravitational pull must be huge. This will attract many bodies towards it. now, as you suggest, they are moving in a direction away from the singularity - then their fine, as would be the case in a stable state universe, or in a constantly expanding universe.

    But what if we take the view of a universe that will expand and contract. As the masses move from expanding to contracting ,the velocities will be small in magnitude and so the black hole may attract more matter.

    Another though is this. If we treat space time as sheet of linen, and matter rests on top like little specs of dust. The black hole pulls in the linen, with the dust on top. So will he whole of space time be consumed by such a black hole?

    Regards,

    Ben
     
  7. chroot

    chroot 10,426
    Staff Emeritus
    Science Advisor
    Gold Member

    Or just tangentially - the matter would simply orbit the black hole, and never fall in.
    Obviously the dynamics of the universe will be different when contracting. The logical leap that black holes will gather more mass in a contracting universe, however, does not seem clear to me.
    These kinds of analogies are dangerous. The "specks of dust" you speak of begin initially at rest with respect to the black hole, which is not a normal state of affairs.

    - Warren
     
  8. I understand the apprehension, however, the real point I was trying to make is that if space time is finite, it will be sucked into the black hole eventually. and the matter will be forced to as well.

    Would they? Bodies orbitting another body (planets round a sun) have slightly collapsing orbits, woudld the same not be true of a body oribiting a balck hole. giving the black hole a 'drain' like effect?

    Regards,

    Ben
     
  9. chroot

    chroot 10,426
    Staff Emeritus
    Science Advisor
    Gold Member

    "Spacetime" doesn't get sucked anywhere. Spacetime is a coordinate system.
    Not in the absence of drag or tidal forces, they don't.

    What I'm trying to explain is that, if the entire milky way galaxy became an enormous black hole, it would have no effect at all on even the nearest other galaxies.

    - Warren
     
  10. Okay, this is about to get messy. If we imagine matter as a 'string' 'woven' through spacetime. As it is pulled into a blackhole is jsut the matter at the pointof entering the singularity absorbed, or is the whole string pulled in (as blackholes can attract time and space)

    So, then why is the Earth collapsing in its orbit to the sun? And why would not the same reasons apply to a planet 'orbiting' a black hole?

    Is this using the principle that the gravitational pull of an object is governed by 1/r^2? And due to distance the effect would be too minimal to draw anything in? And if the black hole has infinite mass, why not infinite gravity (i accept it doesn't as we are notin a black hole - but why not)?

    Regards,

    Ben
     
  11. chroot

    chroot 10,426
    Staff Emeritus
    Science Advisor
    Gold Member

    I have no idea what you're talking about. Please try to use conventional scientific terms, so that your audience will be able to decipher your thoughts.
    Because there -are- non-negligible tidal forces at work in the Sun-earth system. The tidal forces on the Earth caused by another galaxy, on the other hand, are completely negligible.
    You really do seem to be adhering to the "vacuum cleaner" misconception, even while saying you do not. Black holes don't "draw anything in" any more than any other object of the same mass. Black holes also do not have infinite mass.

    - Warren
     
  12. Okay the string idea. Take a Carbon atom.

    It has existed since the beginning of the universe. Therefore, in spacetime, it has occupied many different points, relative of course to space and time. If one connects each of these points, as is logical if one imagines the atom throughout its existance through space and time, a string is formed.

    I am asking, is this string pulled into the blackhole, and therefore the history of the atom or just the atom as it exists at the point it enters the singularity.

    The notion of a planet orbiting a black hole is no different from that of a planet orbiting a star. the principles are still applicable.

    Finally,you said a while ago, that black holes had INFINITE mass. Well not much else has this property so what should I use as a point of reference. and also, as the black hole is of infinite mass in an infinitely small area (a point), the density is infinite. This would make the gravtitational pull infinite would it not? And therefore by using 1/r^2 the entire universe would suffer the infinite pull of the black hole and therefore collapse. This is not occurring so where is the flaw?!

    And
     
  13. chroot

    chroot 10,426
    Staff Emeritus
    Science Advisor
    Gold Member

    This is called a "worldline."
    If a particle's wordline enters a black hole, it says nothing of the rest of the worldline. Its entire history is not demolished anymore than your evening at home is demolished when you walk into school the next morning.
    I didn't think we were discussing a planet orbiting a black hole -- I thought we were discussing a black hole "sucking up" the entire universe.
    I said no such thing. Black holes certainly do not have infinite mass.

    - Warren
     
  14. No, but the fisrst post you made stated:
    If something has infinite density it has an infinitely small volme, infinitely great mass, or both.

    I expect you will say that the volume is infinitely small, making the density infinite or in fact the desnity is not infinte.

    In the case of the former, the infinite gravity wil lexist anyway no?

    And in the case of the latter, then is the black hole not a point in space?!

    Okay - thanks for clearing that up - my common sense was misplaced!



    Regards,

    Ben
     
  15. chroot

    chroot 10,426
    Staff Emeritus
    Science Advisor
    Gold Member

    The classical singularity has zero volume.
    What is "infinite gravity?" Do you mean "infinite gravitational force?"

    - Warren
     
  16. Yes i do.

    Ben
     
  17. chroot

    chroot 10,426
    Staff Emeritus
    Science Advisor
    Gold Member

    If you're just outside the singularity, you'll feel an almost infinite gravitational force. Of course, the classical singularity is not the entire story -- most physicists believe there is no classical singularity, and that quantum mechanics dictates that the mass in a black hole must have non-zero size. Of course, the unification of general relativity and quantum mechanics is far from complete, so no one can definitively answer the question. The best answers I can give you are those from a complete, well-understood theory, general relativity, which is already known have a limited domain of applicability.

    - Warren
     
  18. Okay, I may sound stupid here but that won't be anything new so lets go for it.

    If just outside the singularity there is in an infinite gravtiational force, then surely, in accordance with the relationship of forces (1/r^2), then the force must always be infinite. I believe this lead sto a fallacy as the universe is expanding not contraction.

    So therefore, must one not suppose that the gravtiational force is not infinite - but rather very large?

    And one final question, if I speed towards a black hole from the other side of the universe near the speed of light, and of course become cloesr to the singularity, am i acclerated by it, u ptowards the speed of light further, or am I unaffected due to my speed, surely with infinite gravity, I will be accelerated.

    This leads me on to one more question (sorry) which is, can gravitational effects affect bodies with no mass?

    regards,

    Ben

    Regards,

    Ben
     
    Last edited by a moderator: May 16, 2005
  19. Janus

    Janus 2,453
    Staff Emeritus
    Science Advisor
    Gold Member

    No,
    the gravitational force is infinite at the singularity because r=0. At any r>0 the gravitational force is finite.
     
  20. Thank you for clearing that up.

    Regards,

    Ben
     
  21. russ_watters

    Staff: Mentor

    From the point of view of an observer stationary wrt the black hole, you will continue to accelerate hyperbolically approaching C, but never getting there. From your point of view, you will accelerate constantly, but get to the black hole before reaching C (it doesn't matter how strong the black hole's gravity is or how fast you started - you won't ever reach C).
     
Know someone interested in this topic? Share this thead via email, Google+, Twitter, or Facebook

Have something to add?