How big is a black hole?

Question

Ok I read that "IF" our sun could become a black hole it would be 3km across (they gave this as a size reference) is that the event horizon or the singularity?

Answer 1

thats the event horizon, as a singularity is a single point of
space/time.

Answer 2

Any measurement of the "size" / diameter of a black hole would be in terms of its event horizon, NOT its singularity.

The event horizon of a black hole is the point away from its center at which nothing, not even light, can escape. Anything which falls through the event horizon is for all intensive purposes, lost to the universe. It is the event horizon which is used to measure the size of black holes.

When a mass (any mass) is compressed into a black hole, its reaches a point at which the internal forces resting collapse are no longer able to support the mass under its own gravity, this happens as the object pass the Schwarzschild radius. Once the object has been compressed to this point, the mass collapses into a single point called a singularity.
A singularity is a point. A point has no size of volume. A line is made up of an infinite amount of points.

Density = mass / volume
D = m / v
Since all of a black hole's mass is contained within a single point (the singularity), black holes have an infinite density.


When describing the "size" of black hole which the sun could theoretically form (this will not happen naturally), the size of given in terms of the diameter of its even horizon.

Answer 3

Actually, that's a pretty 'ify' question. Technically speaking, we don't really know for certain black holes exist. There is the scientific evidence that says they do, but as far as I know, one hasn't really been found as of yet. However, it seems to me they probably do. The answer to your question is the event horizon. I seem to remember having read in some astronomy magazine that some scientists think the event horizon for our sun (if it became a black hole) would be three kilometers in diameter in the form of a sphere. We probably read the same articles. However, this is a guess. Some even say our sun is way too small to become a black hole. Others say black holes are only the size of a pinprick in relation to the comparative size-volume of 'regular' space, not compressed space as you would deal with in a black hole. I guess that would be true IF the idea of 'space' as a plenum, which means space as an actual physical aspect of reality that behaves much like a sponge, with matter being the 'water' that fills the 'sponge' (space), is true.

Answer 4

Everyone above is complicating your question rediculously. The answer is simple:
A black hole is a singularity which means it's infinitely small. The event horizon is what has size. Thus, if the sun were to become a black hole, the sun itself would become infinitely small, but its event horizon would be about 3 km.

Answer 5

They are referring to the size of the singularity (the actual matter that has collapsed from the star to form the black hole). The event horizon denotes the area of space that is deformed by the singularities immense gravitational field. It could be very large; many millions of kilometers across.

Answer 6

the second and third answerers are sick.

the ranges of size of the black hole will differ depending on the star that has collapsed. For the event horizon verses singularity size, I really couldn't tell you sorry. No one knows how big a black hole is.

Answer 7

The sun cant possibly become a black hole. If it could, I estimate that would be its sigularity. Actual black holes come in different sizes. Most black holes are about 4-15 solar masses, comepared to our sun, which IS A solar mass. SUpermassive black holes range from about 10^5 - 10^10 solar masses.

Answer 8

from 'Ask a Scientist'

Black hole size

Author: eileenb, kewi a ebersole
How big is a black hole?

Response #: 1 of 1
Author: asmith
A black hole can be any size. The heavier it is, the bigger. For a black hole of the size of a star, I think the size is around 1 kilometer (if the MASS is that of a star, that is). For a black hole with billions of stars in mass, the size would be billions of kilometers.

Answer 9

Our sun is a medium sized planet and will not turn into a black hole. When the sun looses its energy, It will go to supernova and start to collapse to become a neutron star.

The size of a black hole always depend on the size of the the collapsing star.

Answer 10

actually black holes are a point of singularity meaning they have no deminsions, what they probably meant is the Schwarzchild radius was 3 km across, meaning you would have to come within 1.5 km to get sucked into it. If a black hole had the mass of the earth you would have to come within 1 centimeter of it to get sucked in, blackholes aren't really as big and scary as sci fi movies make them out to be.

Answer 11

Any measurement of a black hole is going to be of its singularity in terms of diameter. Why?

You don't know how big a black hole is, neither do I, neither does anyone else...

It can't be mathemetically calculated. :)

To elaborate: a black hole, according to Albert Einstein's Theories of Relativity, is what happens when a star of sufficient mass dies, and does so with sufficient explosive violence that the remaining mass (a minimum of some 30 times the mass of our sun in nature) implodes, or collapses in on itself, getting smaller and smaller as the mass becomes more dense and more dense....

Neutron stars, quasars and such, are what happens to stars that don't quite make it to being a black hole: they can only collapse and in the process concentrate their mass, and gravity (curvature of local spacetime) to the point of making their atoms collapse into nothing but neutrons...these stars are made of, literally, neutronium, which is element zero on the Perodic Table of Elements since it isn't even really an atomic element in nature anymore, just a huge mass of pure sub-atomic neutrons...

But I digress....some of these stars keep on going *past* that neutron star point, sucking in more matter as they go, getting smaller and heavier, smaller and heavier....

until something messed up happens.

Eventually, all of the mass of the dying star...becomes smaller than a neutron, smaller than any *single* sub-atomic particle, and....vanishes. Becomes smaller than what the universe can hold.

This is why the gravity of a black hole is so severe that light itself doesn't escape. This is why neither the true size of a black hole nor its gravity can be calculated...

Well, wait, hold on, we know the size of a black hole. My bad, I jumped the gun.

THERE IS NONE. Literally. Black holes take up zero space, then less than zero space as spacetime folds in on itself and disappears from the rest of the universe. The gravity cannot be calculated because that is based on a density caculation, and you cannot divide any mass, any *number* by zero, it doesn't work.

So...unless you talk to Stephen Hawking on a first-name basis, black holes really only have a handful of things you can say about them:

--they have a mass,
--their *event horizons*, or radius of no return, beyond which light can't escape, has a measurable radius,
--they have magnetic fields on occasion,
--they have a spin or rotation on occasion,
--and by definition they have unlimited gravity that can't be defined by mathematics and literally *don't exist* in our spacetime anymore since they take up NO space....

Sorry for any confusion....but black holes are messed up that way.