Francois Nel asked:
We often hear that blackholes are so massive that even light cannot escape its grasp, therefore light bends when close a blackhole. Come to close and light enters the event horizon and its lost.
Then, why do we hear that black holes spew out particles? Do the particles travel faster than light then?
Kat Arney put this question to Cambridge astronomer Matt Middleton...
Matt - Jets are the most powerful events in the universe - jets from black holes. They carry away huge amounts of material and very often theyíre moving extremely close to the speed of light - say 99.9% of the speed of light. Iím sure that we all roughly remember around our GCSEs - something like this, where you could work out the kinetic energy of a moving body from 0.5 x mv2. Take that mass - oh Katís wondering about it, alright.
Kat - Iím a biologistÖ
Matt - Youíre a biologist - you donít do equations. So if you take the mass thatís coming out of it, take the velocity, clearly thereís a huge amount of energy. And, in fact, thereís a very nearby jet coming from a supermassive black hole called CenA, and the amount of power that is coming from that is 10 to the 12 times the power that is coming from the sun.
Chris - How do we know the jets there?
Matt - You can see it. So these jets in particular emit everything from optical all the way through to x-rays and probably beyond.
Chris - Ah, so the stuff coming out which is radiating thisÖ
Matt - Absolutely. It radiates acrossÖ
Chris - So is it just radiation or is it particles. What is in the jet?
Matt - So it is particles and those particles are radiating. So essentially for those who are on a geek out for some science you have magnetic fields and you have electrons that spiral around those magnetic fields and, because theyíre constantly changing direction, they have acceleration.
Chris - Why are they firing out of the black hole and where from the black hole are they coming from?
Matt - Okay. So, the point is these are not actually from inside the black hole. The old adage of, you genuinely cannot get out of a black hole, is true. You cannot escape from it. And in fact, we should point people to the podcast. But theyíre coming from close to the black hole and, in fact, in another nearby supermassive black hole, people have been able to use radio interferometers. Thatís when you have multiple radio dishes, and they provide a very high angular resolution view of these structures and theyíve been able to work out that itís coming from about 5 times the size of the black hole, above the black hole. So thatís incredibly close.
Chris - Do we know what concentrates the material into a jet? Why isn't it just sort of spinning round, getting excited, and then just radiating in all directions like our sun radiates radiation at us in all directions.
Matt - Sure. So if you ever ask an astronomer a question they canít answer, theyíll always say magnetic fields or dust. It turns out it is magnetic fields and it genuinely is the answer. We know there are magnetic fields there because we see what we call synchrotron emissions, so these are the electrons spiralling around magnetic field lines. And thatís why you basically collimate all this emission thatís coming away from the black hole through these magnetic fields, so it actually does look like a jet. Itís perhaps worth mentioning that thereís aren't the only particles that we see from black holes, thereís also Hawking radiation and thatís when the black hole itself decays. So you have a particle thatís created on the event horizon. Itís actually is a particle-antiparticle pair. One of them goes into the black hole, the other one gets kicked out and thatís how black holes decayÖ
Chris - The black hole loses a little bit of mass and that makes it shrink?
Matt - Absolutely!
Chris - So black holes should evaporate over time?
Matt - And thatís why weíre not going to be destroyed by the Large Hadron Collider.
Kat - Hooray!
Chris - Thatís reassuring to know isnít it Kat?
Kat - It is reassuring.
Chris - Thanks Matt.
The jets are not issuing from the black hole itself (i.e. not from beyond the event horizon) but from the region surrounding the black hole. When there's a lot of material falling in towards the black hole, there are a lot of collisions and it gets very hot. This heating is what's believed to produce the jets. burning, Sat, 27th Jul 2013
Astronomers do not yet have a close-up view of the accretion disk around a black hole, so there are a number of competing theories.
I have a theory that might suggest that light IS actually bending around the the black hole and that's what is being captured in photographs (light that hasn't been captured yet). With refracted light waves, one can actually see the light, such as in a prism. I figure black holes are actually what can be called as the "perfect bond", which can neither move, nor be broken by any of known principle of breaking bonds (chemical or current energy solutions), and is why light can't escape and by which I will describe why in the next section.