Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Mass in black hole?

  1. Feb 26, 2005 #1
    Hi all.

    I was intrested to know if any mass can exist in singularity? Personaly I think I cannot because there are no dimentions or anything, but a friend of mine says that mass can exist(he is not really a physisit and hasn't got much of a knowledge)?

    Who is right?
  2. jcsd
  3. Feb 26, 2005 #2


    User Avatar
    Science Advisor
    Gold Member

    A singularity has all the typical signs of possessing mass. It bends light, stars orbit it, etc. Mass cannot disappear without a trace without tossing most of modern physics into the trash can. Aside from that, singularities are mathematical artifacts. Most modern theorists do not believe they are dimensionless points.
  4. Feb 27, 2005 #3
    so does this mean that mass can exist in a black hole? Are there any dimensions in a black hole?
  5. Feb 27, 2005 #4

    James R

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Black holes have mass. If our Sun suddenly turned into a black hole, the Earth would continue to orbit the hole in exactly the same way it currently orbits the sun. The effect of the black hole's mass is the same as any other equal mass, more or less - so long as you're outside the event horizon.
  6. Feb 27, 2005 #5


    User Avatar

    Too add a little, James mentioned the effect of a black hole is the same as any other equal mass. In general relativity, a key concept to understanding a black hole is spacetime fabric. Let's take a neutron star for example. A star with mass [itex]x[/itex] and density [itex]y_{g/cm^3}[/itex], explodes as a supernova, and forms a neutron star. Well this neutron star will still conserve it's mass [itex]x[/itex] (a little bit of mass is lost as the star's outer layers are blasted off, but it's not important now), but, it's density will now be around [itex]y*10^{15}_ {g/cm^3}[/itex]. Atoms are so tightly packed that the protons and electrons merge into neutrons! So the denser a mass, the more spacetime is curved, the more spacetime is curved the stronger the gravitational force. A black hole is the same way. I used a neutron star because we know more of the numbers than we do a black hole. Right now all we say is a black hole is infinitly dense.
    So, in my opinon, black holes should have mass.
  7. Feb 27, 2005 #6
    I would extent that to: so long as you are outside the equivilant radius of the surface of the equivilant mass.
    The event horizon of a sun-massed black hole would be ~1km in radius.
    But the gravitational effects would start to differ between the two objects as you pass the equivilant distance of the sun's radius.

    -hmm hope my wording is ok to understand :confused:
  8. Mar 1, 2005 #7


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    From what I understand, the following quantities will COMPLETELY describe a black hole (theoretically):

    - mass
    - angular momentum
    - charge

    That is excluded to their observable properties, of course. Inside the event horizon, all bets are off.
  9. Mar 22, 2005 #8
    I am still not too clear about it as my english lacks abit. So would a mass exist inside a blackhole? i.e. Could a mass travel through a blackhole?
  10. Mar 22, 2005 #9


    User Avatar
    Science Advisor

    Actually every black hole has mass, as was already explained. May be you mean ‘matter’ instead of ‘mass’. Black holes form from matter, i.e. fermions (particles with half-integer spin), but they cannot contain any fermions at all, because fermions are destroyed during the gravitational collapse into the singularity. If they would not be destroyed, the Pauli exclusion principle would be violated. The Pauli exclusion principle states that two fermions cannot occupy the same quantum state, or the same place (and the singularity is just one point in space).
  11. Mar 22, 2005 #10
    I can`t think of any way that something with mass could travel through a black hole. Any object that enters a black hole will feel a huge gravitational pull and stay in the black hole.

    Correct me if I`m wrong, but I think it would require an infinite amount of energy to move a massive object out of a black hole.
  12. Mar 22, 2005 #11
    I understand the point you are trying to make, and agree, but think you may be wrong for two reasons:

    1) The gravitational energy released by the suddent collapse of the sun, which, as I am sure you know if you are the same "Jame R" I know and greatly respect from another forum, is not massive enough to become a black hole, but even by just becoming a neutron star/ pulsar it would still blast a lot of energy into space. Earth's side near the sun, certainly the atmosphere, but I bet a lot of the dirt as well, would be blasted into space, changing the orbit of what was left, if anything.

    2) Most of the energy released would not impinge upon any planet, but leave our solar system. Good old E=Mc2 would indicate that the residual "sun" was less masive and the Earth (neglecting point 1 above) would have too much orbit veolocity for current distance from the sun. I.e. it would suddenly be in a more ellipetical orbit climbing towards its new appogee.

    If either 1 or 2 is correct (and I think both are) the Earth's max distance from the sun would very significantly increase.
  13. Mar 22, 2005 #12
    Certainly that is the standard view. If you include "magnetic charge" in "charge" I would completely agree.

    I have a love affair with magnetic monopoles, so even thought there has been only one (not repeatable) observation of them, I think they were created as the standard theory suggests. (That observation was the current step in a supper conducting ring which was what one monopole passing thru the ring should have made.)

    I am very attracted to the idea that back in the early universe when matter was "condensing out of energy" monopoles did form as predicted, but unlike the cooling and becoming neutral baryon / electron mix, they had power to strongly (not weak gravity force only) attract each other over long ranges for eons - "N pole seeking S pole for permanent union and black hole creation" was what a typical classified "sex ads" said back then. (Note that they individually are so heavy that a pair might form a black hole.)

    Don't worry SpaceTiger I won't take this further as i did on our vacuum polarization / black hole exchanges. At least not here and if Chroot (Warren) has his way I will soon be banded form the forum - See my post in the subsection "Quantum Physics" thread about spectral line widths / line frequencys where as usual, you also made a good contribution to recently.
    Last edited: Mar 22, 2005
  14. Mar 22, 2005 #13


    User Avatar
    Science Advisor

    Not exactly the original topic, but magnetic field was added to the list as a must several years ago. So the list is now:

    - mass
    - angular momentum
    - charge
    - magnetic field

    But, I'm not in love with any requirement for "magnetic monopoles"... :yuck:
  15. Mar 22, 2005 #14


    User Avatar
    Science Advisor
    Gold Member

    I have to agree, magnetic monopoles are a non-starter. Theories that predict them, predict them in great abundance and that is not supported by observations. I recall a simple, but haunting argument a physics prof once made: If magnetic monopoles were prolific, they would demagnetize everything.
  16. Mar 23, 2005 #15
    Yes indeed I mean "matter" and what I mean by blackhole is not around it or in the middle of it. I mean just inside the curvature of it. i.e Can a spaceship enter in a blackhole?
  17. Mar 23, 2005 #16


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Anything can enter a black hole -- the problem is that nothing can ever leave it once inside.

    - Warren
  18. Mar 23, 2005 #17
    Here we agree completely.
    This is my I am not fully on board the the never observed, but very standard theory that "Hawkings Radiation" permits mass captured in the point singularity to "get out" with increasing rapidity and the hole "evaporates"

    I.e. consider a black hole at time when its mass is just beginning to drop thru 100Kg and then very shortly later when its mass is 99kg. How did that 1kg "get out" from the point singularity?
  19. Mar 23, 2005 #18


    User Avatar
    Science Advisor

    That has already been covered to the point of overkill. You have to do some serious reading, as this is now to the point of annoying... :frown:
  20. Mar 25, 2005 #19
    So we do not need any space-time fabric to exist?
  21. Mar 26, 2005 #20
    The mass would end up being ripped apart until it was mere atoms and travel towards singularity, but of course you can't just go to the center of the milky way (for instance), shine a flashlight, and hope to see where the matter that's being ripped apart from a nearby star ends up in a black hole

    Agh i hit submit instead of preview (silly tired me :grumpy: ). I forgot to add that the only way we know black holes exist are through theory and by observations of their effect on other celestial objects in the universe. Since light cannot escape from a BH, you can't see it with the naked eye or through a telescope (optical). However if there is a star nearby, the star's hydrogen and helium and other elements it has synthesized through fusion will swirl towards the black holes center (like the water in your sink) and will get accelerated. The material will then release x and gamma rays (due to inverse compton scattering and bremstralung [I know I spelled this wrong... I can never spell this word]). This is something that you can observe and measure with x and gamma ray detectors. Therefore matter can enter a black hole and indeed travel through it. It will never return (as a previous poster mentioned), and you the observer will never see it finish it's travel after it entered (Stephen Hawking has a better description of why this happens... i don't remember sorry).
    Last edited: Mar 26, 2005
  22. Mar 26, 2005 #21
    Wait, I thought black holes absorbed everything that came in contact with them. Wouldn't that mean then we would not orbit the black hole, but instead be pulled into it due to its intense gravatational force?
  23. Mar 26, 2005 #22
    Whoa, hold the phone here calhoon. Do you mean that when a star explodes and becomes a supernova, the protons and electrons of the atoms that made up the mass were brought so close together that they formed neutrons because their charges cancelled out?! :bugeye:
  24. Mar 26, 2005 #23
    Why specifically angular momentum? Mass makes sense, charge makes sense, but I'm not sure about the angular momentum.
  25. Mar 26, 2005 #24
    Pardon my ignorance, but if a mass was able to travel through a black hole wouldn't that make the black hole a worm hole; which only exsist in theory.
  26. Mar 26, 2005 #25
    Please pardon my ignorance again :redface:, but monopoles have been mentioned in several previous posts. What are they?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook