Quote:
Originally Posted by xelasnave
From what I have read I formed the impression that all black holes are part of a binary system. If this is so I wonder why.
I dont know if this is the way it is and if there are black holes that exist as soletary units. Do you know of any exception to my perception of that rule?
Can you provide a pinch of enlightnment on this aspect  .
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A black hole often forms in a binary because of differences in mass of the two stars. A big star in a binary that goes S.N. may form a neutron star that then sucks mass from the secondary in the system. As the mass is deposited, the neutron star can become to large and then collapse to form a blackhole. The dynamics are interesting and are linked to recurrent Nova'sand other interesting stuff.
However, any star big enough may form a black hole. I think the limit is about 20 solar masses but I can't remember exactly.
Summary of fates (very much simplified):
Small star = nova and white dwarf which cools after a long time
Big star = S.N. and neutron star which cools after a very long time, maybe
Massive star = Black hole which does wierd stuff
Its all related to initial mass of the star involved, and the dynamics of the fusion process. If the star is big enough, whether a binary or not, a S.N. will generate an implosion in the core but the resulting object will have to much mass to form a neutron star so the collapse under gravity continues and a black hole results.
Hope this helps