how can a black hole have any circumfrance at all?

Question

i saw this thing on tv about black holes, and they said supermassive black holes are so an so many miles big, and then i thought, if it has infinite density, how can it be any more bigger than a pinpoint?

Answer 1

It is the singularity that has [virtually] no circumference and that generates the black hole.

This is a common error in understanding the wacky stuff that goes on in a black hole.

Go to "Black Holes 101" for more details.

http://ultraviolet-oasis.deviantart.com/art/Black-Holes-101-67694666

Answer 2

Some misinformation here (and a question of my own...)

Answers are correct in stating that the so-called "event horizon" is the radius under discussion. This is the radius at which light, upon entering, cannot escape the gravity of the black hole. It is presumptuous to claim that nothing can escape it.

Actually, answer 3 was on the right track. As a black hole accumulates matter, it's gravity increases, and therefore the distance at which light becomes trapped (by the intense gravity) becomes greater.

To the best of my knowledge (about 20-years-old physics), black holes are *not* infinitely dense. They are simply very large masses dense enough to trap light. I recall reading that the earth would be a black hole if it were compressed to a volume half the size of a golf ball. Clearly, this is not infinitely dense, just very dense. Perhaps the physics theory concerning this has changed in the last 20 years?

Jim, www life-after-harry-potter com

Answer 3

ok a black hole is the region around a singularity from which light cannot escape. it is not a physical boundary.

a black hole surrounds a quantum singularity. this is an object with zero radius and infinite density. the singularity is the remnant of a supermassive star or a relic from the big bang.

it is important to remember the relationship between a singularity and a black hole and the difference between the two.

Answer 4

A black hole does not have infinite density, nothing does. A black hole, three miles in diameter, is considered to be at the centre of our galaxy

Answer 5

A black hole is not a hole. The word hole in this case is misleading. It's a very compact star who's gravity is so strong it does not shine. It's called a black hole because unlike other stars it is dark. Like other stars it's shaped like a ball or is sphere shaped. It stand to reason that as it gathers and sucks in matter it gets larger. Astronomers have located black holes of different sizes all over the known universe.
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Answer 6

The "circumference" they mention is a dimension
of the event horizon. It is not an object 'per se`.
Space/time becomes more and more twisted as
this Imaginary surface is approached.
Beyond it, any prediction of conditions is, at the
present time, pure conjecture.
All we can say about 'density` in relation to
a black hole with any certainty is to
relate observed mass to this surface.

Answer 7

the event horizon would be miles long. the event horizon isnt really the black hole itself, its just the 'point of no return'. once u pass it your not coming back. the black hole itself would be a single geometric point, at the most a size of an atom, possibly smaller.

Answer 8

They would be describing the event horizon, the circumference where it becomes impossible for anything to escape, including light.