Black Hole

[saturno2]

I think ( a hyphothesis), a black hole is not a "hole".
I think that in the center of a black hole there is a " black star" of
neutrons.
This "black star" of neutrons has more density, diameter, magnetic field
and gravity than a pulsar.
It rotates at high speed as a pulsar.
This " black star" is black because it does not emit radiation and
"light off" the photons

[Markus Schwarz]

I think ( a hyphothesis), a black hole is not a "hole".
I think that in the center of a black hole there is a " black star" of
neutrons.
This "black star" of neutrons has more density, diameter, magnetic field
and gravity than a pulsar.
It rotates at high speed as a pulsar.
This " black star" is black because it does not emit radiation and
"light off" the photons

A black hole is an object with an event horizon. Once objects and light pass the horizon, gravity is so strong that they cannot return. Thus, black holes appear black because they don't emit light. Also, since "no material object can travel faster than light" no object can return from inside a black hole. In this sense the black hole is a hole. Inside the horizon everything eventually reaches the center of the black hole. It is yet unclear what really happens there.

In a neutron star, gravity is so strong that is pulls the electrons into the atomic nucleus, resulting in neutrons. Gravity is than balanced by a pressure arising from quantum effects. Once you compress matter even further, no known force can withstand gravity and the neutron star collapses into a black hole.

By now there is strong experimental evidence that black holes exist and that they not just dense "dark stars". For example, the center of the galaxy contains such a large mass in such a small radius that it can only be a black hole.

[saturno2]

In a black hole, the event horizon is an imaginary spherical
surface, through wich the particles fall into the hole only.
We can not see the state of matter in the center of this hole.
It is conceivable, within the possibilitles, that in the center of
a black hole, there is a black star of neutrons, denser than a pulsar

[Chris Peterson]

In a black hole, the event horizon is an imaginary spherical
surface, through wich the particles fall into the hole only.
We can not see the state of matter in the center of this hole.
It is conceivable, within the possibilitles, that in the center of
a black hole, there is a black star of neutrons, denser than a pulsar

The event horizon is not imaginary.

Our physics currently tells us next to nothing about what is inside a black hole. The math tends to suggest a singularity, but most physicists are very uncomfortable with that notion. Certainly, we have few analytical tools we can use to describe what a physical singularity even means.

Outside of some very esoteric and specialized physics, it is probably best to avoid speculation on what is "inside" a black hole. It may not even have an inside in the way we usually think of that word. Asking what is inside a black hole might be like asking what is inside a fundamental particle. A black hole has measurable, understandable properties like mass, spin, and charge. We understand quite well how a black hole operates right up to its event horizon. And for almost all purposes, that is all we need.

[saturno2]

Chris Peterson wrote:
The event horizon is not imaginary.
Wikipedia wrote:
"Event horizon in a rotary black hole
The event horizon is an imaginary surface of spherical form
surrounding a black hole"

[geckzilla]

Chris Peterson wrote:
The event horizon is not imaginary.
Wikipedia wrote:
"Event horizon in a rotary black hole
The event horizon is an imaginary surface of spherical form
surrounding a black hole"

Can you give us a link to the article? I searched for that statement in the Wikipedia article for black hole but couldn't find it. Maybe you are translating from a different language.

[Chris Peterson]

Wikipedia wrote:
"Event horizon in a rotary black hole
The event horizon is an imaginary surface of spherical form
surrounding a black hole"

That sounds like a bad translation. The event horizon is not imaginary. Neither is it a physical surface, so perhaps that is why "imaginary" is being used, but that's not a good word. The event horizon is a boundary, very much a real thing. And its properties are largely the same whether or not the black hole is rotating, so I don't know why that distinction is made in the above reference.

[rstevenson]

I see no harm in using "imaginary" to describe the event horizon. After all, we use imaginary numbers all the time in mathematics, so "imaginary" is not the same, at least in a scientific context, as "unreal." Events can be seen to happen outside the event horizon, and cannot be seen to happen within it. That's all the event horizon is. It's not a place in the usual sense, and may not even be steady and uniform. It exists only as a cusp within the mathematics used to describe black holes. Imaginary is therefore a fine word to describe it.

Rob

[Chris Peterson]

I see no harm in using "imaginary" to describe the event horizon. After all, we use imaginary numbers all the time in mathematics, so "imaginary" is not the same, at least in a scientific context, as "unreal." Events can be seen to happen outside the event horizon, and cannot be seen to happen within it. That's all the event horizon is. It's not a place in the usual sense, and may not even be steady and uniform. It exists only as a cusp within the mathematics used to describe black holes. Imaginary is therefore a fine word to describe it.

Rob

Calling the event horizon "imaginary" is simply inaccurate. It isn't imaginary in the mathematical sense, and it represents a physical boundary, with different conditions on each side. It's no more imaginary than the tropopause in the atmosphere or a thermocline in the ocean. The event horizon is a physical, measurable thing; it isn't just a consequence of mathematics, seen only in equations.

Not being a solid surface does not make something imaginary.

[saturno2]

geczilla
You are right
The original article is in Spanish and this is the link

http://es.wikipedia.org/wiki/Horizonte_de_sucesos

But imaginary in English is " imaginario" in Spanish.
The article uses the phrase " superficie imaginaria" = imaginary surface
There is no mistaking .

[geckzilla]

Several articles do call the surface imaginary. I'm not sure why. I'm in agreement with Chris's assessment. This article calls the event horizon impossible to observe which I'm not sure I agree with either. It would seem to me that if the hole were in front of some kind of object, the entire sphere could be observed. Something like a distant nebula or a transit of a nearby star would suffice.

[rstevenson]

I picture the event horizon using this analogy...

Take two magnets and place them near each other. Each will attract iron filings, as usual. But there is a "surface" between them which can be defined as the collection of all points where the magnetic force pulling filings towards one magnet is precisely balanced by the force pulling filings to the other magnet. Iron filings dropped near that surface will be attracted to one side or the other of it, eventually reaching one magnet or the other. We can use a suitable equation to calculate where that surface is, yet there is nothing there. We have to imagine it, hence it's an imaginary surface.

Similarly, there is nothing at the event horizon of a black hole -- or to be more precise, nothing hangs around long enough to form what we usually call a surface. There's nothing physically there to look at, yet its location is made visible by the lack of light below it.

I'm quite comfortable describing the event horizon as a very real phenomenon while also calling it an imaginary surface.

Rob

[geckzilla]

Light must be imaginary then since I can't see it passing through a vacuum.

[Beyond]

Maybe you're seeing it from the back side?

[geckzilla]

You're imaginary too, Beyond. I can't see you.

Joking aside, I see your point, Rob. But while I agree there are imaginary aspects to trying to visualize a magnetic field in one's head, I disagree that a magnetic field ("surface" or otherwise) is imaginary. Otherwise it wouldn't exist anywhere but my mind.

[Beyond]

Maybe it would help a little if you thought of it as a 'place', where you may or may not see anything, depending on what's happening.

ha-ha, i can't see you either, O hidden one. But once in a while i get a glimpse. So i can tell you're around.

[Beyond]

All this time spent talking about a black hole. I just can't see it.

[Chris Peterson]

I picture the event horizon using this analogy...

Take two magnets and place them near each other. Each will attract iron filings, as usual. But there is a "surface" between them which can be defined as the collection of all points where the magnetic force pulling filings towards one magnet is precisely balanced by the force pulling filings to the other magnet. Iron filings dropped near that surface will be attracted to one side or the other of it, eventually reaching one magnet or the other. We can use a suitable equation to calculate where that surface is, yet there is nothing there. We have to imagine it, hence it's an imaginary surface.

No, it isn't. Like an event horizon, or the other examples I gave previously, it's a field boundary. There's nothing imaginary about it. The space around the magnets has physical, measurable properties. The boundary is characterized by the nature of the magnetic field. A test body will behave differently at the boundary than elsewhere. We need imagine nothing; instruments will precisely map it.

"Imaginary" is a very poor and misleading word to describe physical boundaries like these.

[neufer]

CORIOLANUS: My nobler friends,
[list] I crave their pardons:
For the mutable, rank-scented many, let them
Regard me as I do not flatter, and
Therein behold themselves:[/list][/color][/i]

<<A misconception concerning event horizons, especially black hole event horizons, is that they represent an immutable surface that destroys objects that approach them. In practice, all event horizons appear to be some distance away from any observer, and objects sent towards an event horizon never appear to cross it from the sending observer's point of view.

An observer crossing a black hole event horizon can calculate the moment they have crossed it, but will not actually see or feel anything special happen at that moment. In terms of visual appearance, observers who fall into the hole perceive the black region constituting the horizon as lying at some apparent distance below them, and never experience crossing this visual horizon. Other objects that had entered the horizon along the same radial path but at an earlier time would appear below the observer but still above the visual position of the horizon, and if they had fallen in recently enough the observer could exchange messages with them before either one was destroyed by the gravitational singularity. Increasing tidal forces (and eventual impact with the hole's singularity) are the only locally noticeable effects.>>

[saturno2]

Chris Peterson wrote:
" The event horizon is not imaginary. Neither is it a physical surface."
You are right
But the article is right, too. Why?
The article not says:
The event horizon is imaginary.
The event horizon is a surface.
It says: " The event horizon is a < imaginary surface> "
The event horizon " seems" a surface.
The phrase < imaginary surface> can not get her out of context and
divide it into two simple words.
We handle many things imaginary: lines, axes, points, numbers ( imaginary
numbers), etc

[Chris Peterson]

Chris Peterson wrote:
" The event horizon is not imaginary. Neither is it a physical surface."
You are right
But the article is right, too. Why?

Sometimes, it isn't a simple matter of "right" or "wrong". Something can be "right" (or at least, not "wrong") and still be poorly worded, or described in a confusing way.

"Imaginary" can mean different things, and in the context of the event horizon isn't necessarily wrong. But that doesn't change the fact that it's not a very good word choice, and in something like a Wikipedia article, designed to educate a lot of people, it's especially inappropriate (given all the different ways people might interpret "imaginary").

If the English Wikipedia article on black holes used that terminology, I'd make an edit- either remove it, or expand upon it.

[geckzilla]

I sort of understand how a moving observer could not see itself crossing an event horizon. But the stationary observer dropping the object in? What's that about? What if the observer remotely drops the object and watches it fall from a perpendicular angle to the drop path? Would it be any different from an observer watching the object from straight above the object?

Aquaporins and black holes. What a funny mix of things to have in my head.

[Chris Peterson]

I sort of understand how a moving observer could not see itself crossing an event horizon. But the stationary observer dropping the object in? What's that about?

An outside observer does see objects cross the event horizon. If you yourself fell into a black hole, however, it would take infinitely long to reach the event horizon- in your reference frame- due to time dilation. From your viewpoint, you would asymptotically approach the horizon but never reach it.

[geckzilla]

Ok,

http://www.hawking.org.uk/into-a-black-hole.html

Although you wouldn't notice anything particular as you fell into a black hole, someone watching you from a distance, would never see you cross the event horizon. Instead, you would appear to slow down, and hover just outside. You would get dimmer and dimmer, and redder and redder, until you were effectively lost from sight.

The crossing of the event horizon is not observed but that doesn't mean that the object never disappears. That's what I needed. Otherwise black holes would be covered in red crap.

[Beyond]

Aquaporins and black holes. What a funny mix of things to have in my head.

Perhaps your sub-consciousness is telling you that the heat we now have in this part of the country (the extreme heat generated around the black hole), is sucking the water out of you fast (represented by the Aquaporins), and that you should stay in air conditioning and drink more water Of course that was a funny thing to have in my head. But I'm already in air conditioning, and i just had some water.