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Singularity or just a very small, massive shell?

  1. Sep 17, 2011 #1
    The nature of a black hole is that gravity attracts objects at a speed faster than light making it impossible for them to be able to escape but if the object is accelerating towards the black hole it would slow down and become more massive the close it got because it is approaching the speed of light and as such would never reach the center. Instead the mass would just form an extremely massive shell around the center but would never actually reach the center. I was just thinking about this on my own and never heard anyone mention it so I assume that there must be some flaw in my logic or that I just haven't studied enough. Can someone please enlighten me on the subject?
  2. jcsd
  3. Sep 17, 2011 #2
    Where is the basis for objects slowing down as they accelerate?
  4. Sep 17, 2011 #3
    They would be approaching the speed of light due to the black hole's gravity as they accelerate inwards causing time to slow down. Please excuse my wording as they wouldn't be "slowing down" in relation to speed but instead time would go very slowly for the object compared to the rest of the universe making it take a very long time (for us) for the object to get any closer to the center. In addition the closer it got to the center the slower time would move for the object as it would have accelerated even more within that time frame.
  5. Sep 17, 2011 #4
    Thats an interesting point I've never thought of. I don't know enough Relativity to say what an object falling into a black hole would appear to look like from other reference frames, so I think someone else needs to answer you here.

    My guess is this doesn't matter because even though it may appear to take infinitely long to fall into the singularity, it doesn't appear that way to anyone else (imagine a ship traveling at 99.9999...% c leaving Earth heading to the sun, while it may take infinitely long for the people on the ship to experience the time it takes to hit the sun, from an outside observer they would just smash into the sun in 8 minutes).
  6. Sep 17, 2011 #5
    I think you're backwards with the effects of moving near the speed of light. To the people on the space ship it would take 8 minutes to hit the sun but for the people on earth it would seem that it took them an extremely long time. This is due to the fact that light must be measured as traveling at the same speed from all points of reference. The people on the ship would travel at a very slow speed and be become very compact (flat) so that when they measure the speed (distance/time) of light it would still come out the same as the people on earth. The ship would also become very massive in order to have the same amount of energy without surpassing light speed.
  7. Sep 17, 2011 #6
    If that is the case then why don't we see light as motionless?
  8. Sep 17, 2011 #7
    Because light has no mass. It is pure energy making it able to travel at the fastest possible speed. That is why we measure light to be the maximum speed possible because all mass will be unable to reach that speed and therefore fall short.
  9. Sep 17, 2011 #8
    I'm getting myself confused, and it's a bit too late for me to pull out the Lorentz equations to see if i'm thinking about that correctly (if this is still unresolved tomorrow I might do that). But I'm pretty sure I'm right here, the last thought experiment I can think of is this:

    The concept of accelerating to near-light speed velocities to accomplish interstellar travel within a human lifetime (for the passengers onboard the ship) is well established. If time dilation works like you are saying, this would be impossible like this:

    Lets say you are moving at a speed infinitely close to c. You are traveling to a star approx. 100 ly away. If light worked the way you said it does, then it would still take 100 years for the astronauts to reach the star, and they would all be dead.
  10. Sep 17, 2011 #9
    Yes, this is what I'm saying. That is why even if we could accelerate close to the speed of light it would still take a very long time to reach another planet which makes people either use multi-generational space ships or the use of huge amounts of mass and energy to pull space towards them shortening the distance between the two locations.
  11. Sep 18, 2011 #10


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    You are assuming black holes can arise by virtue of relativistic mass increase. This does not occur. If an object is not sufficiently dense to form a black hole in its own reference frame, it is not a black hole in any reference frame.
  12. Sep 18, 2011 #11
    Anyone out there !! Are there any theories stating that the matter falls exactly into the center of a black hole? Not to be rude, am just a beginner. thank yo :)
  13. Sep 18, 2011 #12
    What about once the original singularity forms? What will happen to other matter that falls towards the black hole? Will it ever reach the center?
  14. Sep 18, 2011 #13
    Matter will fall exactly toward the center of a black hole because that is where the strongest gravitational attraction is. This thread is about if the matter actually ever makes it into the center of a black hole.
  15. Sep 18, 2011 #14
    K...got it !! But why do you think it would ever form a "shell" like thing ? Couldn't it be "as it is" and stop at one point somewhere near the center?
  16. Sep 18, 2011 #15
    Ya but I was thinking that mass would be coming in from all sides so the shell would be roughly uniform with stopped matter creating the "shell". Most of the mass making up the shell would probably be hydrogen so if a larger object fell in it would be as you described just stopping "as it is" at some point near the center.
  17. Sep 18, 2011 #16
    Being simple n straight, why hydrogen??
  18. Sep 18, 2011 #17
    Because that's the most common element in space. The center of the black will probably contain the heavier elements the star fused so the shell will likely contain hydrogen from space and from the part of the star that was blown away during the end of the red super giant phase. Helium will also be in the shell as well as any other matter that was brought into the black hole after the singularity formed.
  19. Sep 18, 2011 #18


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    Em370 what are you basing any of this on? It is my understanding that current models predict a gravitational singularity beyond an event horizon though contemporary understanding is that this is due to a limitation of current science. There is a thread going over this https://www.physicsforums.com/showthread.php?goto=newpost&t=226671

    Please note that overly speculative posts and unsubstantiated personal theories are not allowed at PF
  20. Sep 18, 2011 #19


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    From the perspective of an outside observer the infalling mass does not slow down, processes in the mass do. E.g.

    A clock falls into the black hole
    It falls at the rate and acceleration you would expect
    However the rate of it's ticking keeps slowing down

    From the perspective of the clock things are different e.g.

    A clock falls into the black hole
    It falls at the rate and acceleration it would expects
    It's own rate of ticking is constant
  21. Sep 18, 2011 #20
    Okay reading back I realized I probably phrased this really poorly. I learned that a black hole is an object with a gravitational force faster than the speed of light which is why it is called a black hole since light can't escape. I also learned that as things approach the speed of light they experience time at a rate different from those not traveling at that speed. I just want to know if something that falls into a black hole will actually ever reach the center or if the gravity of the black hole will cause it to travel towards the center so fast that it will experience time so slow that to us outside the black hole it will seem to never reach the center. The stuff I said about the shell was just speculation as to what it would look like if we could see inside the event horizon. I apologize if this seems insubstantial I really don't know that much about what happens past the event horizon.
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