Black Hole

Myrddin

Hi guys, Im just wondering about this lately, hopfully someone has the answer or an input.

We've all seen the black hole analogy, a whirlpool on a 2d plane but has a third dimension (event horizon). In reality though, space is 3 dimensional, therefore how would a black hole actually look (if you could see it) in 3d? Are there any hypothetical models for this online?

Im trying to imagine a sphere which has collapsed in on itself, is the black hole still a sphere albeit much smaller. And does the event horizon lead inwards from all directions? Hope Im making some form of sense....

Spear

EnterNow wrote: »

Hi guys, Im just wondering about this lately, hopfully someone has the answer or an input.

We've all seen the black hole analogy, a whirlpool on a 2d plane but has a third dimension (event horizon). In reality though, space is 3 dimensional, therefore how would a black hole actually look (if you could see it) in 3d? Are there any hypothetical models for this online?

Im trying to imagine a sphere which has collapsed in on itself, is the black hole still a sphere albeit much smaller. And does the event horizon lead inwards from all directions? Hope Im making some form of sense....

They're spheres, accretion disc/gas jets not withstanding.

Kevster

As I understand, black holes 'emit' radiation. However, it's at wavelengths outside of the visible wavelength for humans. Therefore, as long as the black hole isn't 'feeding' from some other star, then it would just appear black and nothing more. You could look at it from any angle and it would look the same.

Hoovers

EnterNow wrote: »

Hi guys, Im just wondering about this lately, hopfully someone has the answer or an input.

We've all seen the black hole analogy, a whirlpool on a 2d plane but has a third dimension (event horizon). In reality though, space is 3 dimensional, therefore how would a black hole actually look (if you could see it) in 3d? Are there any hypothetical models for this online?

Im trying to imagine a sphere which has collapsed in on itself, is the black hole still a sphere albeit much smaller. And does the event horizon lead inwards from all directions? Hope Im making some form of sense....

I think the best way to to think of a Black Hole goes something like this:

-After a sufficiently massive star collapses at the end of its life, the gravity is so great that a Singularity will form- A point of infinite gravity in spacetime.

-The event horizon is the region, spherically, around the Singularity that absolutely no information, not even light can escape once past the horizon.

So in answer to you're question, if you could see a black hole, it would be spherical, with a single point, the singularity at it's center.

(Note that the Event Horizon is a region and not a physical entity)

The 'whirlpool' model you mentioned is called an embedding diagram and it's a 2D analogy of what happens in 3D spacetime. So the hole, represented by a circle, is the 2D analogue of a sphere.

Recommended reading is Black Holes and Time Warps by Kip Thorne. It's the bible on black hole theory and other amazing stuff predicted by General Relativity!:D

Brian_Uckfast

Actually, there is new evidence now that black holes dont exist

Spear

Brian_Uckfast wrote: »

Actually, there is new evidence now that black holes dont exist

Source?

Brian_Uckfast

Spear wrote: »

Source?

http://www.guardian.co.uk/science/2006/jul/29/spaceexploration.uknews

I read somewhere else that they can only exist if you believe in them

Myrddin

Hoovers wrote: »

The event horizon is the region, spherically

Thats what I wanted to know, cheers.

Re the non existence of black hole theory, how would the plasma phenomonon explain gravitational lensing? Accrection discs etc?

Kevster

What's at the center of every galaxy then? - A 'mere' neutron star and not a so-called 'supermassive' black hole? I mean, they've evebn seen jets of matter outfalling from the center of galaxies. That indicates that something is there feeding on matter from other obects. Do Neutron starrs do this?

Hoovers

Brian_Uckfast wrote: »

Actually, there is new evidence now that black holes dont exist

Roger Penrose proved in a theorem with Hawking that a sufficiently massive collapsing star will always form a Singuarity. Therefore a black hole.

Kevster

Hoovers, that was only proven using mathematics and not actual observations. I mean, I think that it was once proven using mathematics that you could place a beam of some length into a room, when in reality it was clearly impossible. Mathemetics isn't an exact representation of the real world... ...and much of our theories in Cosmology are not proven.

Hoovers

Kevster wrote: »

that was only proven using mathematics and not actual observations

Ah yeah I know- It would be news of the millennium if somebody actually observed a singularity!
But I take your point. However, I think that the theorem only adds to some compelling indirect observations made over the past few decades, along with nearly 100 years of serious research by some of the greatest minds in history. And, if you believe what General Relativity has to say, then it predicts that singularities are an inevitable consequence of the collapse of sufficiently massive stars.

So, quick ques Kevster, do you not think that singularities exist?

Kevster

Do I believe that they exist? - Not really, actually. I think that the presence of a singularity in our theories indicates that there's something wrong with the theory in itself. Like, do you actually believe that there are points of 'infinite' density out there? I think that there probably are objects out there that have a huge density, but - urrgh - I dunno... ...I'm only an amateur astronomer and cosmologist!

Hoovers

Ah thats fair enough, just wondering what your thoughts are on the subject... I suppose it comes down to what you believe at the end of the day.
But like I said, If as I do, believe the theory of General Relativity, a theory which has stood some of the most rigorous tests time after time since it was published, then singularities are included in our universe...:eek:

stiff kitten

also known as hell

Kevster

There seems to be a fair bit of research work going on with black holes recently. One group has deduced that they could have formed from Dark Matter 'caving in' on itself and then subsequently dragging in 'normal' matter with it. Other scientists have recently discovered jets of water emanating from a black hole (indicating that it's 'feeding' on something with water on it in the first place).