How to define a black hole?

[reciprocity]

A black hole is most appropriately thought of as a point mass, i.e. a tremendous amount of mass concentrated in a zero-dimensional space.

There is often confusion that a black hole exerts an infinite amount of gravitational force. If you go beyond one solar radius, a black hole that is one solar mass would not be any different gravitationally than the sun.

[Austin Liv]

Originally Posted by Lang Sicherung

I think you're a little off there.

Although still not precise, much better would be science defining all "things" as matter or energy. Which are continuously converting into each other, back and forth

With THAT as your starting point, black holes are easily understood... think DENSE MASS... very DENSE

Infinitely dense!

[Guest053011]

According to NASA a black whole is a thing: it is a frozen collapsing star.

I recall a consumer scientific magazine explaining that if earth were to pass through one of these, it would fit comfortably into a teaspoon.


http://science.nasa.gov/astrophysics...s/black-holes/

Don't let the name fool you: a black hole is anything but empty space. Rather, it is a great amount of matter packed into a very small area - think of a star ten times more massive than the Sun squeezed into a sphere approximately the diameter of New York City. The result is a gravitational field so strong that nothing, not even light, can escape. In recent years, NASA instruments have painted a new picture of these strange objects that are, to many, the most fascinating objects in space.

Most black holes form from the remnants of a large star that dies in a supernova explosion. (Smaller stars become dense neutron stars, which are not massive enough to trap light.) If the total mass of the star is large enough (about three times the mass of the Sun), it can be proven theoretically that no force can keep the star from collapsing under the influence of gravity. However, as the star collapses, a strange thing occurs. As the surface of the star nears an imaginary surface called the "event horizon," time on the star slows relative to the time kept by observers far away. When the surface reaches the event horizon, time stands still, and the star can collapse no more - it is a frozen collapsing object.


WAY COOL:

Another interesting possibility becomes available when the black hole is in a binary star system with a compact star like a neutron star or another black hole. When two black holes orbit each other, their accelerated masses directly create gravitational waves that stream away through space and carry information about the masses and strong fields that created them. Gravitational waves are waves of space curvature and may be detected by missions such as the Laser Interferometer Space Antenna (LISA) through the way they affect the geometry of space at the location of the detector. In a sense, a black hole is the mass it contains plus the intense gravitational field around it, so LISA will actually be able to "see" black holes. From these observations, astronomers will be able to study the details of the gravitational field around the black hole and measure all the parameters of the black hole - its mass, its spin, and its location in the sky.

[Guest053011]

Originally Posted by atlcomedy

I'd rather skip dinner.....


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But apparently it's okay for you to be a complete jerk.

[reciprocity]

Originally Posted by Lauren Summerhill

According to NASA a black whole is a thing: it is a frozen collapsing star.

I recall a consumer scientific magazine explaining that if earth were to pass through one of these, it would fit comfortably into a teaspoon.


http://science.nasa.gov/astrophysics...s/black-holes/

Don't let the name fool you: a black hole is anything but empty space. Rather, it is a great amount of matter packed into a very small area - think of a star ten times more massive than the Sun squeezed into a sphere approximately the diameter of New York City. The result is a gravitational field so strong that nothing, not even light, can escape. In recent years, NASA instruments have painted a new picture of these strange objects that are, to many, the most fascinating objects in space.

I think you are confusing a neutron star with a black hole. Like austin_liv mentioned, a black hole is infinitely dense. Density is mass/volume so volume has to be zero for this to equal infinity. This also means a black hole has zero length, width, and height.

When the "size" of a black hole is referred to, the implicit reference is to its Schwarzschild radius (or the distance from the center of the singularity where the gravitational acceleration is equal to the speed of light).

[NinaBrooke]

Originally Posted by atlcomedy

Such class...

are you related to Charles Tudor?

Take it like a man and don`t complain, please. You had it coming (and deserve it) .. As they say : You should not shout into the woods if you can`t handle the echo!

[Can I Play Too???]

Originally Posted by reciprocity

I think you are confusing a neutron star with a black hole. Like austin_liv mentioned, a black hole is infinitely dense. Density is mass/volume so volume has to be zero for this to equal infinity. This also means a black hole has zero length, width, and height.

Since when are you allowed to divide by zero?

Of course, no one has a PHD in physics here and the responses were over simplified but wiki is not ok to use as a source because it can be edited quite easily.

[Camille]

Black hole: something that everyone on this board at has at one time or another been guilty of digging themselves into.

C xxxxxx

[Guest071711]

Theres a book "Black Holes And Warped Space Time" I reccoment it to you. Many interesting theories on black holes

[Guest071711]

Originally Posted by Camille

Black hole: something that everyone on this board at has at one time or another been guilty of digging themselves into.

C xxxxxx

[reciprocity]

Originally Posted by Can I Play Too???

Since when are you allowed to divide by zero?

Dividing by zero is fine under many conditions. Of course, you don't really get the full picture in high school algebra. 0/0 is undefined but since the mass is positive and you would be approaching zero volume from the positive side, "divide mass by zero volume to get infinite density" is well-defined.

Of course, no one has a PHD in physics here and the responses were over simplified but wiki is not ok to use as a source because it can be edited quite easily.

Let's not jump to conclusions =P

[Wwanderer]

Originally Posted by Lauren Summerhill

As the surface of the star nears an imaginary surface called the "event horizon," time on the star slows relative to the time kept by observers far away. When the surface reaches the event horizon, time stands still, and the star can collapse no more - it is a frozen collapsing object.

This is correct, but note the important phrase "the time kept by observers far away". For an observer falling into a black hole (i.e., according time kept in that frame), there is no material object "frozen" by time dilation. Rather there is the disappearance of the mass of the collapsing object into a singularity (a point of zero volume), leaving only a region of pure space-time curvature behind.

Thus, what a black hole is depends on the observer...is meaningful only "*relative* to the observer", as befits a prediction of Einstein's General Theory of Relativity.

Btw, the Russian term for one of these objects means "frozen star" and thus emphasizes the perspective of the distant observer, whereas the English term "black hole" gives more importance to that of an infalling observer.

-Ww

[heidilynnla]

You were more tolerable when you looked like Johnny Depp

Originally Posted by charlestudor2005

Actually, the question evokes in the mind a lot of smart aleck responses.

[Mazomaniac]

Originally Posted by Can I Play Too???

Of course, no one has a PHD in physics here . . . .

I wouldn't be so sure about that.

Geeky scientists need love too, ya know.

Cheers,
Mazo.

[abdclub]

Camille,
Smart AND beautiful ...... what a combo!!!!!

abdclub