Thread: black holes

why is it that black holes emit energy? and why is it perpendicular to the shape of the rest of the system?

Because information cannot be destoyed. They omit energy streams at their polar regions.

I'm not sure that's the correct answer. The black holes don't really "emit" energy, anything that crosses the event horizon is in there to stay. Period.
But Hawking radiation is believed to be emitted from just outside the event horizon, and that takes energy from the black hole.

Originally Posted by Neutrino

I'm not sure that's the correct answer. The black holes don't really "emit" energy, anything that crosses the event horizon is in there to stay. Period.
But Hawking radiation is believed to be emitted from just outside the event horizon, and that takes energy from the black hole.

Erm. So where do you propose that hawking radiation comes from ?

Originally Posted by leohopkins

Erm. So where do you propose that hawking radiation comes from ?

The brilliant mind of Stephen Hawking - however there are scientists who question it, mere mortals like us sit open minded waiting to see who is the victor.

Active galaxies show as having huge jets of energy thusting out from the galaxy's polar regions. Is this not proof alone that some black holes occassionally radiate ?

Furthermore, would anyone care to hazard a guess as to what might happen should two neighbouring active galaxies "jet streams" collide ?

I think you are confusing 'quasars' with black holes, if black holes 'shot out jets of flame then the one thats 28KLY away would keep the night sky lit up and the earth devoid of life'

No. we are now pretty certain that there is a black hole at the heart of every galaxy. Active galaxies (i.e when the black hole is feeding) show up as having huge jets of energy radiating from the polar regions.

http://www.astro.umd.edu/education/a...al/actgal.html

Thankyou for the link Leo.

Now perhaps you might like to read the whole article - it is the acretion disk around the black hole which is thought to emit the gas jets - not the black hole.

Yes but the jets only occur when the black hole is actually feeding, which tells me there is a definate relationship between the black hole's activity and the acretion disk. There must be some kind of communication between the two.

Then to be scientifically correct the black hole does not emit the radiation, but the blackhole-acretion system does.

It's not emitted FROM the black hole, it's certainly emitted because of the black hole's gravity but it's not FROM the black hole itself. I think it's an important distinction. That goes for the jets and for the hawking radiation.

Nutrino

Hawking radiation does not rely on there being any more than a blackhole to exist, it is theoretically proposed to be the ultimate leaking of energy - resulting in the final decay.

THe jets are dependant upon there being both a black hole and a acretion disk (a ring of matter arbiting the BH and slowly being drawn in). It is an interaction between the two which causes the disk to emit the gas jets.

Originally Posted by Megabrain

Nutrino

Hawking radiation does not rely on there being any more than a blackhole to exist, it is theoretically proposed to be the ultimate leaking of energy - resulting in the final decay.

THe jets are dependant upon there being both a black hole and a acretion disk (a ring of matter arbiting the BH and slowly being drawn in). It is an interaction between the two which causes the disk to emit the gas jets.

I agree? But in both cases the radiation or material isn't being emitted from inside the event horizon is the point I was making.

You and I agree clearly that the BH supplies the power but not the fuel - leo has to come to this understanding - I'm sure his original misconception was probably due to reading it from a poor source.

BH supplies the power yes. But how does the black-hole get this power to supply it ?

Leo,

From your link, I quote -

"As surrounding galactic material moved toward the center, it would form an accretion disk around the black hole. Friction in the accretion disk could slow the material enough to cause the material to fall into the black hole. This would cause the inner part of the accretion disk to become very hot. The hot, inner part of the accretion disk would then be capable of producing jets of hot gas and radiation streaming out of the nucleus along the axis of rotation of the disk. These jets would be observable at radio wavelengths. If the disk were thick, the jets would be focused into narrow beams. Such beams have been observed in active galaxies, for example, in the center of the giant elliptical galaxy M87 and NGC4261."

I think you are missing my point somewhat. :?

I like this dance. May I cut in?

I just want to touch on a few points I read;

These "jets" are known as bipolar flows. It is material from the accretion disk. This material follows the magnetic field of the BH or neutron star (and even protostars). The key distinction is that "polar" refers to the magnetic poles - not the poles of rotation.

Seems like someone enquired where Hawking radiation comes from. Steve (as I know him...) envisioned that particles can pop in and out of existence - but they pop in pairs - matter and the antimatter partner. If they "pop" in the right spot (i.e., near the event horizon), one can get sucked in while the other escapes - thus they cannot annihilate each other. Now the details of BH evaporation are still a bit fuzzy to me, but as I understand it, since it would appear that the particle which escaped was emitted by the BH - and has a positive energy, to conserve energy, the other particle would have negative energy, which would take energy away from the BH - hence, slowly evaporate it as this process continues.

I think Leo said something about active galaxies. These are also called AGN's (active galactic nuclei). This is just a galaxy with a supermassive-BH in the center with a lot of gas around it (forming an accretion disk). You can imagine galaxies with BH centers but not much gas to "feed" it. These are just plain ol' galaxies (and... there may be smaller galaxies without the BH center...?).

Quasars are thought to be similar to AGN's except that they are very far away - and thus reveal galaxies near the time when they were forming. But, like AGN's, they are thought to be supermassive-BH's fed by accretion disks.

And Leo asked, where does the BH get its power. The accretion disk could be called the "food," but the "hunger" comes from gravity itself.

Oh... and those who stated that the event horizon is the point of no return are correct (as to my knowledge...). Nothing can escape from within the event horizon (except maybe gravity waves and the graviton if it exists - i.e., gravity itself...).

Cheers,
william

Interesting. I think the existence of black holes would completely disprove "gravitons" on the basis of a paradox. That a black holes gravity could in the end get so strong that its gravity would cease to exist and would no longer pull matter in to it.

The black-hole's magnetic field ?? Hmmmm

As for particle pairs popping into existence and immediately annihalating each other. Well, this happens quite a lot yes, but they annihalate each other almost instantanously which to me suggests that they are in very close proximity to each other when they are first created and to suggest that one of them could be sucked in by the black hole while the other remains unharmed seems to be a little, um, difficult to grasp, as that would mean that one of the particles would have to be created just the other side of the event horizon. If it were not then this could not happen. However strong a black-hole's grqavitational pull is, it is STILL not as strong as the magnetic, weak and strong forces. Even though it it acts over an infinate range.

Gravity is one of two things here. It is either caused by the warping of space-time, in which case gravity is supplied by the space-time fabric OR if indeed gravitons come into play then that would mean that it is the black-hole itself that is supplying energy to any acretion discs.

We all know that a neutron star is just a huge bunch of quarks. If indeed gravitons exist. Could a black-hole just be a huge bunch of gravitons?

Originally Posted by leohopkins

(...)

As for particle pairs popping into existence and immediately annihalating each other. Well, this happens quite a lot yes, but they annihalate each other almost instantanously which to me suggests that they are in very close proximity to each other when they are first created and to suggest that one of them could be sucked in by the black hole while the other remains unharmed seems to be a little, um, difficult to grasp, as that would mean that one of the particles would have to be created just the other side of the event horizon. If it were not then this could not happen. (...)

Remember that the event horizon is not there -it's like a cloud; a cloud is not there, what is there is a place where condensation happens... :wink:

The event horizon is the point where escape velocity=c; not less and not more, and not a matherial thing rather a "place".

What Hawking says (at least what I got from reading his 1977 Scientifc American article) is that a particle/antiparticle couple could be understood as two particles, one of which is travelling backwards in time, and thus with divergent trajecories. Then, if one is "bearing" towards the event horizon and the other away from it, a particle would fall inside and the other would escape -yet all energy would come from within the black hole itself, jsut we would never know that there's a particle going backwards in time as it would be beyond the EH. :?

Also, I figure that whenever the hole intakes matter, this matter actually may "pull" the event horizon before crossing it, so a couple could find itself inside/outside in the process of creation... I wonder if there's a mathematical model on how matter could affect the EH at the entry point...

Aren't we forgetting somthing? Heat radiation?

the black hole emits about a millionth of a split degree divided by the size of the black hole(or somthing like that, I dont have the formula in my head.)
This means that it is possible it is possible to go pass the event horizon.( i guess)

as i understand it, the effects of gravity from a BH are limited to distance. at some point away, what ever is in orbit, will just stay in that orbit as it passes the so called horizon. its not stated, but i assume the speed of the orbit should be a factor.

If a gravitons do indeed exist, they would be, i would guess a massless boson, similar to a photon. So it is entirely possible that as bosons can exist at the same place at the same time then all of the gravitons could exist inside a singularity, regardless of number. The actual number of gravitons, dictating the strength of the gravitational field and thusly the radius of the event horizon. Who knows, maybe the graviton is the ONLY truly fundamental particle there is. ?

there is nothing like graviton.
it is just a theoretical particle.
gravity is not caused by a particle or by a wave.

Originally Posted by basim

there is nothing like graviton.
it is just a theoretical particle.
gravity is not caused by a particle or by a wave.

Well it's always nice to see somebody has all the answers!

Originally Posted by Megabrain

Originally Posted by basim

there is nothing like graviton.
it is just a theoretical particle.
gravity is not caused by a particle or by a wave.

Well it's always nice to see somebody has all the answers!

He is just another KNS

Basim:
how old are you?
what makes you think youre smarter than the scientific community?
especially einstein, planck, and schrödinger?

are you even a member of anykind of IQ community?

Originally Posted by basim

there is nothing like graviton.
it is just a theoretical particle.
gravity is not caused by a particle or by a wave.

Actually, all particals are theoretical, that's why it's called the atomic THEORY

Originally Posted by Nevyn

Originally Posted by basim

there is nothing like graviton.
it is just a theoretical particle.
gravity is not caused by a particle or by a wave.

Actually, all particals are theoretical, that's why it's called the atomic THEORY

calling them particles is wrong, calling them waves are wrong, its something else wich we are unable to describe but got the propeties of waves and particles

Just to make things clear
Theory dont mean "think" "guess" or any other simular meaning word you can think of

Originally Posted by Zelos

Originally Posted by Nevyn

Originally Posted by basim

there is nothing like graviton.
it is just a theoretical particle.
gravity is not caused by a particle or by a wave.

Actually, all particals are theoretical, that's why it's called the atomic THEORY

calling them particles is wrong, calling them waves are wrong, its something else wich we are unable to describe but got the propeties of waves and particles

Just to make things clear
Theory dont mean "think" "guess" or any other simular meaning word you can think of

May I suggest calling them wavicles ?

Yeah you can suggest it!

than can you make it clear to me what exactly is gravity?
and what is the role of graviton in gravity?
graviton are made of what?

Not aware of what a graviton is, apart from a hypothetical particle which I think has now been discounted as a seperate, unique particle. And No I canot tell you exactly what gravity is, and neither can anyone else!

There is a 'space time curvature' cop out but it is not a complete explanation.

THe only factual statement we can truly, honestly make is "Gravity is the phenomemun exhibited by mass whereby in free space mass tends to attract other mass at a predictable rate" - and today, that's it, same as when Newton around....

why is that we cant block gravity or we cant put a barrier to overcome the gravitational force?

Originally Posted by basim

why is that we cant block gravity or we cant put a barrier to overcome the gravitational force?

i think your mixing gravity with energy principles. energy, an emission from a source and no longer dependent on the source for existence. if the sun became non-existent in a flash, all that had been emitted would not be affected. gravity is an attraction toward mass to other mass, with limitations. if this mass becomes extinct, there is no gravity and anything previously attracted will lose this attraction.

there is no physical barrier (that we know of), other than distance. at any point a particular gravity pull will be lost. whether from other forces, i think is questionable. as for over coming gravity; this is very easy and trajectory and speed will evade any gravitational pull. the earth moving at 20mps or 70k miles per hour in its travels around the sun avoids being pulled into its much greater attraction. the trajectory of some of our space probes, will leave the influence of solar gravity, as well.

Originally Posted by basim

why is that we cant block gravity or we cant put a barrier to overcome the gravitational force?

We do not understand the origins of gravity, we have a bunch of formula that can predict it's effects but that's not the same. As we do not know by what mechanism it works we cannot counter it.