# Black holesWatch

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Thread starter 1 week ago
#1
What determines the size of a black hole?
The singularities would be all the same size presumably.
So what determines the radius of the event horizon??
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1 week ago
#2
Its mass.
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Thread starter 1 week ago
#3
(Original post by Sinnoh)
Its mass.
The curvature of space time depends on the mass right? So why doesn’t the star bend space time as much as the black hole it forms if they both have the same mass.
Sorry if these seem like dumb questions
Last edited by JakeTSR; 1 week ago
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1 week ago
#4
(Original post by JakeTSR)
The curvature of space time depends on the mass right? So why doesn’t the star bend space time as much as the black hole if they both have the same mass.
Sorry if these seem like dumb questions
Remember that it also depends on the size of the object (not that I am at all versed in GR). Gravitational field strength is proportional to and for any mass M, for it to be a black hole its radius has to be less than or equal to where c is the speed of light. This is just what you get from rearranging Newton's laws of gravity.
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1 week ago
#5
the "size" of a black hole depends on how massive it is (easy) and how fast it is spinning (not so easy).
the curvature of space-time depends on mass distribution (ie. density), clearly packing more mass into a smaller space is going to have a bigger effect, otherwise the whole universe would be a black hole.
a singularity pretty much by definition has zero size, so the best you can do to quantify the "size" is the size and shape of the event horizon.
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