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There are at least two different ways to describe how big something is. We can say how much mass it has, or we can say how much space it takes up. Let's talk first about the masses of black holes.
There is no limit in principle to how much or how little mass a black hole can have. Any amount of mass at all can in principle be made to form a black hole if you compress it to a high enough density. We suspect that most of the black holes that are actually out there were produced in the deaths of massive stars, and so we expect those black holes to weigh about as much as a massive star. A typical mass for such a stellar black hole would be about 10 times the mass of the Sun, or about 10^[31] kilograms. (Here I'm using scientific notation: 10^[31] means a 1 with 31 zeroes after it, or 10,000,000,000,000,000,000,000,000,000,000.) Astronomers also suspect that many galaxies harbor extremely massive black holes at their centers. These are thought to weigh about a million times as much as the Sun, or 10^[36] kilograms.
The more massive a black hole is, the more space it takes up. In fact, the Schwarzschild radius (which means the radius of the horizon) and the mass are directly proportional to one another: if one black hole weighs ten times as much as another, its radius is ten times as large. A black hole with a mass equal to that of the Sun would have a radius of 3 kilometers. So a typical 10-solar-mass black hole would have a radius of 30 kilometers, and a million-solar-mass black hole at the center of a galaxy would have a radius of 3 million kilometers. Three million kilometers may sound like a lot, but it's actually not so big by astronomical standards. The Sun, for example, has a radius of about 700,000 kilometers, and so that supermassive black hole has a radius only about four times bigger than the Sun.
Originally posted by Kaytagg
. . .cease to exist at any place in the universe. . .
The Question
(Submitted September 12, 2001)
At the center of a black hole the singularity point has zero volume and infinite density. I know that the singularity is a point in space rather than an object with specific dimensions, but how is it possible for something to have zero volume and infinite density?
The Answer
This is indeed difficult to grasp. Actually at the center of a black hole spacetime has infinite curvature and matter is crushed to infinite density under the pull of infinite gravity. At a singularity, space and time cease to exist as we know them. The laws of physics as we know them break down at a singularity, so it's not really possible to envision something with infinite density and zero volume. You might check out the web site for further information on black holes and singularities:
antwrp.gsfc.nasa.gov...
Hope this helps,
Georgia & Koji
For "Ask an Astrophysicist"
Originally posted by harrytuttle
I'm sure us hacker-humans will figure out a loophole in the rules of the universe so that we can someday take a peek.
Originally posted by Kaytagg
Can you point out what you think I'm missing in his post?
Originally posted by C-JEAN
Originally posted by Kaytagg
Can you point out what you think I'm missing in his post?
Hi again, Kaytagg.
You are right. I am a little too vague. . . B-)
My point is that the "radius" discussion tells it all.
1- The radius between the "surface" of the inside "DENSE ball" and
the horizon of whole, is a constant.
2- The horizon varies in size, as ...overdose's quote says.
+-10 Km, +-30 Km ?? +-10 miles, +-100 miles. . .etc. . .
3- So, if the horizon varies in size(s), then
there is a ball with a "surface", inside, that varies too. . .
Blue skies.