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Black hole

  1. Sep 10, 2005 #1
    What makes black hole so heavy even it's tiny in size? :eek:
  2. jcsd
  3. Sep 11, 2005 #2
    Well, It is a star at least 10 times the Sun's mass that has collapsed in on itself, and with such high densities it has a huge (infinite) gravitational pull towards the singularity, or center of a black hole. All the stuff pulled into a black hole will innevitably be crushed into the infinately dense singularity.

    Answer your question?
  4. Sep 11, 2005 #3
    All the "stuff" including light.
    Hence the color, "black" :biggrin:
  5. Sep 12, 2005 #4


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    Welcome to Physics Forums, anarchy.spirit

    Active stars have a balancing act where the inward pressure of all their mass is counterbalanced by the outward pressure of the fusion reaction in the star's core. When the star dies and the fusion reaction in the core stops, the star's matter crunches inward under its own weight/gravity. The end result depends on how much matter there is being crushed down. A star like our sun will compact down to an object called a white dwarf which will be about the size of the planet Earth. Larger stars crush down to something even smaller...a city-sized object called a neutron star. Even larger stars crush down to a point thereby creating a black hole. So, it's small, but it's made from a lot of mass.
  6. Sep 12, 2005 #5


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    Phobos is describing a heirarchy of degenerate matter in star collapse. When the mechanism supplying a star's outward pressure fails, the star will collapse. Depending on the mass of the remains of the star, it may end up as a white dwarf (in which the Pauli Exclusion principle prevents atoms from being compressed beyond a certain point because the electrons resist being forced together) or as a neutron star (in which the electrons and protons have been forced to combine to produce neutrons, but the neutrons again obey the Pauli Exclusion principle and resist further densification). Then, there are the more extreme mass star remnants - these are expected to form black holes hidden behind event horizons which hide their properties from our universe.
  7. Sep 12, 2005 #6


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    isnt our sun is expected to become a red giant?
  8. Sep 12, 2005 #7


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    A white dwarf is what's left when a red giant runs out of fuel for fusion and blows away its outer layers, leaving the core behind. See red giants and white dwarfs.
  9. Sep 14, 2005 #8
    Hence the color, "black" :biggrin:[/QUOTE]
    Do you mean that the black hole is perfectly black?
  10. Sep 14, 2005 #9
    Blackholes can't be seen directly, because light cannot escape them. They are detected from the X-rays that the accretion disks they form. When material falls into a black hole from a companion star, it gets heated to millions of degrees Kelvin and accelerated. The superheated materials emit X-rays, which can be detected by X-ray telescopes such as the orbiting Chandra X-ray Observatory. The star Cygnus X-1 is a strong X-ray source and is considered to be a good candidate for a black hole. Stellar winds from the companion star, blow material onto the accretion disk surrounding the black hole. As this material falls into the black hole, it emits X-rays.
    Last edited: Sep 14, 2005
  11. Sep 14, 2005 #10
    The end result depends on how much matter there is being crushed down. ]
    If so,how the informations in the balack hole can be retraced?I recently heared that "Stephen Hawkings" accepted that there is a non zero poosibility for getting back the information that is absorbed by the black hole due to its gravity.
  12. Sep 23, 2005 #11
    Stephen Hawking has stuck to his guns regarding the ultimate loss of information from black holes in our Universe.
    However, his new theory uses the many worlds/sum over histories hypothosis and states that there are sufficient (ie:- a majority of) alternative Universes, where the prevailing physics prevents the formation of black holes and hence any loss of information.
    Locally, individual Universes may lose information, but these comprise a minority of the total number of possible Universes. Therefore, overall there is no loss of information.
  13. Sep 24, 2005 #12
    is the space in a black hole constant or does it undergo any revolution or rotation?
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