How could a super massive black hole come about?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by fedr808, May 18, 2011.

  1. fedr808 1100101 Valued Senior Member

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    Okay, the way I understand it (with my knowledge of physics being that of physics 2 so I still have a ways to go) is that a black hole will form when an object has enough mass to be compressed into a sphere less then a certain radius.

    So basically, from what I know the second a star collapses with enough mass in a small enough space it will form a black hole.

    So how can a supermassive black hole form? The instant a star (or the corpse of one) gains too much mass it will collapse.

    So how can a star ever gain enough matter to form a supermassive black hole if it will collapse long before it can ever get to that point?
     
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  3. AlexG Like nailing Jello to a tree Valued Senior Member

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    Black holes can increase in mass via accreation.
     
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  5. ScribJellyDonut Registered Senior Member

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    A supermassive black hole would never form from a star collapsing into a black hole. If I recall the largest theoretical size (look up jeans mass/radius) for a star is about 200 solar masses. A black hole does not form when there is 'enough mass' by the way. When a star would collapse under its own mass, it in fact has outward pressure from the fusion within the star that prevents this from happening. The fuel will eventually exhaust from fusion, and then the outward pressure will not be able to counteract the gravitational collapse. The star will blow off most of its mass in the supernovae, while the core of what is generally iron (in supergiants) will remain. In stars of high mass, the gravitational force/acceleration will exceed the neutron degeneracy pressure and it will therefore become a black hole somewhere between 2 and 200 solar masses (my lower limit may be incorrect as it's been a while since I've done the calculations). Regardless, this is far form the circa billion solar mass sizeof a supermassive black hole, which are believed to exist only in the center of galaxies.

    :EDIT:
    So in short the answer to your question is that supermassive black holes do not form from a collapsing star = these form 'regular' black holes instead. These stars do not collapse as soon as they form because of fusion in the core that raises the temperature and creates an outward pressure that counteracts the gravity.
     
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  7. fedr808 1100101 Valued Senior Member

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    I would think that would take far too long.
     
  8. fedr808 1100101 Valued Senior Member

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    Okay, thanks for your response. But my essential question is how can enough mass can come together to form a supermassive black hole without prematurely collapsing into a normal black hole.
     
  9. AlexG Like nailing Jello to a tree Valued Senior Member

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    We're not talking about a BH drifting in the vast emptyness of interstellar space, sucking in the odd hydrogen cloud. We're talking about the galactic center, were you have many black holes forming and merging, while sucking down solar masses. The lifetime of a galaxy is easily long enough for a supermassive BH to form by merging and accretion.
     
  10. fedr808 1100101 Valued Senior Member

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    So what your saying is that since theyw ere created during the big bang (or at least early on) when there was a high density of matter/energy in a given part of space (because the universe was still pretty small) they were able to absorb energy/matter much more quickly then modern day black holes can since everything has become much more spread out?
     
  11. AlexG Like nailing Jello to a tree Valued Senior Member

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    Nice summation.
     
  12. fedr808 1100101 Valued Senior Member

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    Okay, thanks.
     

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