Black Hole query ref. AN Feb Page 11

[G1ZmO]

From Astronomy Now (Feb) Page 11 "Black hole's jet of death"

"Jets are generated by the powerful magnetic fields around supermassive black holes, which sweep up charged particles such as protons and electrons that have become trapped in a disc around the black hole at the center of galaxies" The particles are then funnelled away in a pair of jets that blast out along the vertical axes of the galaxies"

Can anyone explain in simple terms how the jets of particles refered to can be streaming AWAY fro the black hole?

I would have thought that, even far from the event horizon, the forces acting on particles would still be attractive (towards the black hole) and not repulsive?

Paul

[ringz]

The trouble with jets is that no-one really knows how they work. There's lots of conjecture but with the distances involved it's a bit difficult getting the observations to see right into the processes that are actually creating the jets.

--

Martyn

[Macavity]

Yes, one begins to sense there is no "shame" (nor solitude) in not knowing why...

"The mechanisms for the creation of jets[1] and the composition of jets[2] are still a matter of much debate in the scientific community" (http://en.wikipedia.org/wiki/Relativistic_jet) etc. etc.

[Astroman]

From what I know, (which isn't really that much), it's a matter of trajectory, combined with the orientation of the magnetic field, and the polarity of the particle being ejected.

Simply put, a particle is falling toward a black hole. Most fall right in, but above circumstances may cause the particle to be deflected by the magnetic field and propelled away, or it may simply just barely miss the "sweet spot" of the hole and do a "lip out", as a golf ball around the hole. If the latter, the field propels it out along the pole in one direction or the other, depending on the particle's charge.

HTH.

[coatesg]

Can anyone explain in simple terms how the jets of particles refered to can be streaming AWAY fro the black hole?

I would have thought that, even far from the event horizon, the forces acting on particles would still be attractive (towards the black hole) and not repulsive?

The gravitational force on a particle near the black hole will be large, but as long as any object is outside of the event horizon, it can always escape given enough energy. The further from the BH, the lower the gravitational attraction (inverse square law) between the BH and the particle and so it's easier for a particle to make it away from the BH.

In the case of the jets from BHs, the source of the jet particles is actually some distance from the BH event horizon where the particles can be driven away (the "outwards force" on a particle is greater than the "inwards force"). I think studies of M87 have shown the jet forms within a few tenths of a light year away from the black hole, and the jet actually narrows somewhat from the source after being fairly wide angled at first.

[Tiny]

I did enquire here who invented the term 'Black Hole' but the message seems not to have arrived. Wonder where it went. Anyway, unlike more immediate dangers from out there, the Black Hole name seems to be one that should win a prize for engaging the imagination of Joe Public.

Incidently, doesn't Hawkin radiation come in somewhere with what comes out of Black holes?

[G1ZmO]

I think Karl Jansky was one of those who first predicted the presence of black holes and was one of the founders of radio astronomy.

[Macavity]

Mr. Hawking claims the term "Black Hole" was "coined in 1969 by American scientist John Wheeler...". OK, I cheated and looked! The question as to - What was the SOURCE of all this matter being "flung about", also occured to me? With no evidence (or theory), I'm guessing it's "external" matter getting sucked into the process. There must(?) be SOME component of "Hawking radiation" - Essentially from quantum splitting of the vacuum and then rendering the "virtual" particles, real? But who knows what the "ratio" is... If indeed that is the question! :mrgreen:

[coatesg]

Incidently, doesn't Hawkin radiation come in somewhere with what comes out of Black holes?

Kinda - it appears to come "out" of black holes - it (theoretically!) comes from pair formation (quantum fluctuation in the vacuum allows a particle-antiparticle pair to briefly form and annihilate from a vacuum) at very close to (but outside) the event horizon.

One of the pair disappears over the event horizon, and the other stays outside. To an observer, the particle that is outside the event horizon appears to have been emitted from the black hole's event horizon, and the mass of the black hole has decreased.

Clever, but with nasty complex theories lurking beneath the surface!

[Kaptain Klevtsov]

Having just watched the C4 Hawking program I'm even more confused that usual. The program described a pair of particles being conjoured up out of nowhere as is supposed to be the norm these days. Now I can see that if these two particles sum to zero there is no problem with conservation of mass or energy so my non-quantum physics understanding isn't offended. What struck me as odd was the idea that the particle with negative mass got into the black hole while the positive mass bit got away. I was under the impression that gravity worked on mass and as such the positive mass bit would get a tug from the BH, whereas the negative mass bit might even find itself being repulsed by the BH.

Any pointers as to why that might be?

Kaptain Klevtsov

[Macavity]

Hi, KK! Bothered me too... But I can only quote (scan) Prof. Hawking:

Because energy cannot be created out of nothing, one of the partners in a particle/antiparticle pair will have positive energy, and the other partner negative energy. The one with negative energy is condemned to be a short-lived virtual particle because real particles always have positive energy in normal situations. It must therefore seek out its partner and annihilate with it. However, a real particle close to a massive body has less energy than if it were far away, because it would take energy to lift it far away against the gravitational attraction of the body. Normally, the energy of the particle is still positive, but the gravitational field inside a black hole is so strong that even a real particle can have negative energy there. It is therefore possible, if a black hole is present, for the virtual particle with negative energy to fall into the black hole and become a real particle or antiparticle. In this case it no longer has to annihilate with its partner. Its forsaken partner may fall into the black hole as well. Or, having positive energy, it might also escape from the vicinity of the black hole as a real particle or antiparticle. To an observer at a distance, it will appear to have been emitted from the black hole. The smaller the black hole, the shorter the distance the particle with negative energy will have to go before it becomes a real particle, and thus the greater the rate of emission, and the apparent temperature, of black hole.

SO THERE! But I think anyone can be forgiven (even remaining slight) confusion? :mrgreen:

From a "Brief History of Time" - Copyright Bantam Press - And (vaguely) claiming "reviewers rights"

(Hey, BUY THE BOOK!) and because this seems to be an interesting GENERAL question here...

[Kaptain Klevtsov]

I've got the book and have read it at least four times. Once I've read the book its all clear, for five minutes.

"because real particles always have positive energy in normal situations." What does that mean? Is it supposed to be "normal" sat on the event horizon, or would you expect wierd stuff to happen? In normal situations there are no black holes, virtual particles (with or without negative energy or gravity) or even bendy space. Does my head in this stuff.

Kaptain Klevtsov

[Tiny]

If memory serves I didn't like what it said on page 37.

[Kaptain Klevtsov]

Yeah, that whole heliocentric bit is a bit off the wall isn't it?

Kaptain Klevtsov

[barkis]

Heinrich Hertz said, " One cannot escape the feeling that these mathematical formulae have an independant existence, and intelligence of their own, and that they are wiser than we, wiser even than their discoverers, that we get more out of them than was originally put in."

This quote from the book Deep Time by David Darling. The journey of a sub-atomic particle from the moment of creation to the death of the universe- and beyond.

Ron.

[Tiny]

And then we get to imaginary solutions to nice easy equations. Or maybe the imaginary exists somewhere. Whet about winding numbers with rubber balls turning inside out if cut up the right way.

Find a solution to every question - this thing could run and run. Or - there is a solution to everything but it takes rather longer than this Universe has got to find the solution. Still it keeps people in work.

[supernova]

42