# How many dimensions are there in a black hole

vinayjain
Can anyone tell me that how many dimensions are there in a black hole and which are the dimension

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Homework Helper
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vinayjain

can u please tell me the name of those four dimensios which exists in black hole

Homework Helper

I just did: after "executive summary" in post #2.
3 time-like and 1 space-like.

If you want to know what that means you'll just have to read the links.
There's no royal road for this one - sorry.
Perhaps if you told me what you want to know for?

vinayjain

thank you very much for the quick and fruitful reply and I did not want specially anything I am just curious to know about black holes.........again a heartest thanks

alzheimer

those are very useful informations and links, thanks to all, keep it up..

Homework Helper

No worries and happy hunting :)

I find that pairing references like this can help - the Berkely FAQ will help refine questions. You get all the way through it and you have a chance of understanding the Haldenwang paper ... even if you don't follow the math.

Homework Helper

No worries and happy hunting :)

I find that pairing references like this can help - the Berkely FAQ will help refine questions. You get all the way through it and you have a chance of understanding the Haldenwang paper ... even if you don't follow the math.

vinayjain

can anyone please clarify my doubt related to black hole i.e. when black suck objects inside event horizon it hits singularity but it obtain some space in black hole then it must lead to a conclusion that the size of black need to be increased as time pass (when black hole is in active mode) so this means that supermassive black hole has gone through this process and hence quasar is formed. please clarify

mkarger

There's a massive distance between the event horizon (which is nothing more than an optical barrier) and the hypothesized singularity.

There are theories about how black holes both accrete and shed mass. But that is not necessarily related to the formation of quasars.

Quasars are formed from the accretion disk surrounding black holes. They are considered to be early objects within the time span of universal expansion.

vinayjain

There's a massive distance between the event horizon (which is nothing more than an optical barrier) and the hypothesized singularity.

There are theories about how black holes both accrete and shed mass. But that is not necessarily related to the formation of quasars.

Quasars are formed from the accretion disk surrounding black holes. They are considered to be early objects within the time span of universal expansion.

The thing is this that there is massive distance between event horizon and hypothesized singularity of a massive black hole but when a black hole is not that big then these forces act very soon..........

vinayjain

and related to formation of quasar that is what i am asking if a small black hole suck lots of things its mass could increase and thus there is a formation of accretion disk and thus quasar is that is the process?

Staff Emeritus

and related to formation of quasar that is what i am asking if a small black hole suck lots of things its mass could increase and thus there is a formation of accretion disk and thus quasar is that is the process?

Sure. How do you think quasars initially formed? The only problem in todays time is that one of the only places there is a high enough concentration of mass to form a quasar is in the center of a galaxy. Which usually happens to already have a supermassive black hole that has already absorbed most of that mass. So we don't really have the conditions to form many quasars at this point in time.

Gold Member

A quasar could care less about the presumed 'singularity'. All the radiation is emitted from outside the event horizon, as has already been noted.

Staff Emeritus

can anyone please clarify my doubt related to black hole i.e. when black suck objects inside event horizon it hits singularity but it obtain some space in black hole then it must lead to a conclusion that the size of black need to be increased as time pass (when black hole is in active mode) so this means that supermassive black hole has gone through this process and hence quasar is formed. please clarify

As the mass of a black hole increases, the radius of the event horizon from the center also increases. It is currently unknown about the ultimate fate of matter and energy that falls into a black hole and passes the event horizon, so no one can really say much about the singularity.

Homework Helper

How long would it take for something to enter a black hole, from the pov of someone well outside it?

NOte: smallest BH found has about 12km to the center, and the biggest (stellar) BH has 50-odd kms. Not that far.

The galactic-center supermassive is supposed to be 13-14million kms to it's center so there you'd be travelling a while. There is a tendancy to think of these things as super-dense as well, like stellar BHs, but that need not be the case.

vinayjain

according to the different studies given on internet it is said that according to the observer who is looking at a black hole it would take a huge amount of time which is considered to be as forever but on the other hand the thing which is falling in the black hole (supermassive) it would take around 7 seconds to hit singularity and for black hole (small in size) gravitational pull will tear the object apart before even entering the black hole.

vinayjain

As the mass of a black hole increases, the radius of the event horizon from the center also increases. It is currently unknown about the ultimate fate of matter and energy that falls into a black hole and passes the event horizon, so no one can really say much about the singularity.

Probably the thing is when a black hole pulls enough things inside that can increase its radius to an extent where the end side escape velocity is less than velocity of light we see that there is an object emmitting light but actually it is the black hole which has increased its size to that extent (and it may true that's how a quasar is generated)

vinayjain

can anyone please tell that is it possible that even black holes magnetic poles inside it

Homework Helper

BHs can have mass, spin, entropy and charge ... spinning charged hole will have a magnetic field. This would be a Kerr Black Hole. You can also get a magnetic field without spin ... see:

As for magnets inside them - Haldenwang
http://members.cox.net/jhaldenwang/black_hole.htm
- discusses the possibility of our Universe being inside a BH. That would include magnets.

If it takes an infinite time for an object to cross into a BH, viewed from a outside, then in what sense would a BH increase it's mass over time?

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Staff Emeritus

Probably the thing is when a black hole pulls enough things inside that can increase its radius to an extent where the end side escape velocity is less than velocity of light we see that there is an object emmitting light but actually it is the black hole which has increased its size to that extent (and it may true that's how a quasar is generated)

I don't think any of that is correct. To my knowledge once inside the event horizon (which is what is expanding when the black hole increases in mass) it is not possible for anything to get back out.

Staff Emeritus

If it takes an infinite time for an object to cross into a BH, viewed from a outside, then in what sense would a BH increase it's mass over time?
Perhaps the in-falling mass adds to the mass of the black hole (or rather the strength of the gravitational pull in the area around it) making the event horizon expand? Not sure.

vinayjain

I don't think any of that is correct. To my knowledge once inside the event horizon (which is what is expanding when the black hole increases in mass) it is not possible for anything to get back out.

the statement which i made might be incorrect on which u quoted sir but the thing is if anything cannot come out after crossing the event horizon then how could the gases at accretion disk gets heated up in quasar which have a supermassive black hole at centre............

Staff Emeritus

the statement which i made might be incorrect on which u quoted sir but the thing is if anything cannot come out after crossing the event horizon then how could the gases at accretion disk gets heated up in quasar which have a supermassive black hole at centre............

The accretion disk is outside of the event horizon.

Perhaps the in-falling mass adds to the mass of the black hole (or rather the strength of the gravitational pull in the area around it) making the event horizon expand? Not sure.

Indeed, the event horizon begins to expand BEFORE the mass crosses the horizon from an outside observer's perspective (as noted, it will never do so). The event horizon's size increases asymptotically to the value it would have if we just assumed the the object fell in immediately.

vinayjain

The accretion disk is outside of the event horizon.

I know that accretion disk is outside the event horizon I am asking that how does the gases present in accretion disk heats up and radiate so that it make the visible from millions of light year and named as quasar.

Means there is a phenomena that heats up the gases to an extent that they radiated.........

vinayjain

If it takes an infinite time for an object to cross into a BH, viewed from a outside, then in what sense would a BH increase it's mass over time?

actually it takes infinite time on the perspective of an outside observer but actually it takes a very short amount of time to fell in black hole after crossing event horizon..........

Staff Emeritus

I know that accretion disk is outside the event horizon I am asking that how does the gases present in accretion disk heats up and radiate so that it make the visible from millions of light year and named as quasar.

Means there is a phenomena that heats up the gases to an extent that they radiated.........

From wikipedia:
The most spectacular accretion discs found in nature are those of active galactic nuclei and of quasars, which are believed to be massive black holes at the center of galaxies. As matter spirals into a black hole, the intense gravitational gradient gives rise to intense frictional heating; the accretion disc of a black hole is hot enough to emit X-rays just outside of the event horizon. The large luminosity of quasars is believed to be a result of gas being accreted by supermassive black holes. This process can convert about 10 percent of the mass of an object into energy as compared to around 0.5 percent for nuclear fusion processes.

Here's the article: http://en.wikipedia.org/wiki/Accretion_disk

mkarger

I know that accretion disk is outside the event horizon I am asking that how does the gases present in accretion disk heats up and radiate so that it make the visible from millions of light year and named as quasar.

Means there is a phenomena that heats up the gases to an extent that they radiated.........

The accretion disk heats up because it's being compressed.

vinayjain

The accretion disk heats up because it's being compressed.

How????

Staff Emeritus

How????

When a material, especially a gas, is compressed it heats up.

mkarger

How????

When you compress a body, you are putting energy into it. This raises particles to higher energy states. In an attempt to reach equilibrium (ground state), the matter will shed energy in the form of light and heat.

(This is, of course, a simplified explanation)

mkarger

Forgot to mention drag friction. A critical component.

Because of conservation of angular momentum, the matter stretches out as it spins. Like pizza dough. Which causes gravity to pull at different strength in different parts of the spinning matter. Because the disk does not act as a solid body, these forces cause a lot of differential speeds. Which results in large amounts of friction loss in the form of light and heat.

Homework Helper

actually it takes infinite time on the perspective of an outside observer but actually it takes a very short amount of time to fell in black hole after crossing event horizon..........

So - do you mean to suggest that a BH increases it's mass at a finite rate only from the pov of an observer following the mass?

We would not expect to measure the mass of a black-hole from the pov of something falling into it would we? Surely we'd stand back and observe the schwarzchild radius (somehow) as mass falls into the BH. (Otherwise, how do we get the data back to the lab?)

So, such an observer measuring the radius against time would see what?

If it takes an infinity of the observers time for the BH to increase it's mass, surely the graph of radius against time will be flat?

Note: these are pedagogical guiding questions.

There has been a part-answer already: what happens to the schwarzchild radius as the matter approaches it? Still, what sort of time scale are we talking about?