h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Just read this story: http://news.bbc.co.uk/1/hi/sci/tech/7148671.stm which details how a jet of particles from a black hole is bombarding a nearby galaxy.

My question is how does this work? I thought black holes simply sucked things in, with no hope of escape - how could a black hole be ejecting matter?

I'm not the person for a definitive reply - not by a long way.

I think the key though is in the statement "A handful of these galaxies eject powerful jets from the vicinities of their black holes".

I seem to remember Stephen Hawking in "A Brief History of Time" (I think) talking about how these jets work, but I think it is the case that they happen near, and are caused by, black holes. They don't come "from" the black holes for the reason you state.

Again, I have no definitive answer to this, but I seem to recall it being something to do with the fact that most black holes have a 'spin', like the Earth. I think the jets are usually emitted along the axis of the spin, from the north and south poles, as it were.

firstly, particles in this case are electrons and photons so the terminology of 'ejecting matter' isn't really right. Hence why these jets can travel at up to 98% the speed of light (perhaps more but I ain;t heard of such).

Secondly, no, they don't eject matter, the accretion disk does. Sort of.

Round the black hole you have the swirling mass of particles, matter etc that is being dragged into the black hole. As it does so it is naturally compressed and heated up. This causes it to radiate - electrons, photons, and various other things in the EM spectrum - which is why they are generally investigated using radio and X-ray telescopes.

The actual direction of the jets is along the axis of rotation - I'm not too clear whether the ejection is due to gravitational fields, magnetic fields or most likely a combination. Anyway, the energy comes from the conversion of matter outside of the event horizon. As I understand it anyway, where it can escape.

The jets you see are the results of matter being compressed and heated and contorted in the accretion disk round the hole giving off energy (due to that process) in the form of particles. These particles move at a good proportion of the speed of light along the axis of rotation.

Hey, it was over a billion years ago, let it go!

There is also supposed to be a form of radiation Hawking recognized and gave his name to, which can escape a black hole, so they're not entirely "black".

Still though - I just love the idea of a "death beam" irradiating a whole planet in a matter of seconds.

Puts stuff like this --> http://news.bbc.co.uk/2/hi/entertainment/7149525.stm in context, I'd say..

Sweet (original) article. But - electrons aren't matter?

Here is NASA's take on it and where the BBC got it from.

http://science.nasa.gov/headlines/y2007/18dec_assault.htm?list189499

And here is a quick explanation of the way jets occur from NASA Goddard Spaceflight Centrre.

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/990923a.html

turvy

Are black hole jets the explanation for the bars in barred galaxies?

Electrons are matter. Although they are very small and light, they do have measurable mass.

"But - electrons aren't matter?"
they're energy aren't they? All that wave/partical dualism stuff?

I think you're thinking of photons, which are light 'particles'. I'm not really a physicist, though, so if I'm glaringly wrong then please someone put me out of my misery.

you could well be right.
I get too confused about all this sort of stuff. You think of electrons as discrete particles arbiting the nucleus, then you find out actually they're sort of smeared all over the universe or whatever.

I think I got confuddled! I was just concerned that saying 'matter' would conjure up images of large chunks of rock being lobbed at passing galaxies rather than a stream of particles.

Photons = the quanta of electromagnetic radiation = energy.

Electrons = particles with mass and charge (regardless of defined "shape") = matter.

If I've learned anything of astrophysics in the last few years, its that spectacular phenomema from large objects are always magnetic. Think about the auroras on earth when high-speed particles from the sun are channelled down the earth's magnetic field lines. This is probably something similar, whereby the black-hole's rotation accelerates matter up to stupid speeds before the magnetic field lines at the poles spit them out. Maybe .

Hooray! I got a physics one right! Can I have one on sport now, please Bob?

Ah well, not the first, and no doubt not the last, embarressing post on here for me. All I can say is I know what I meant . Shame I couldn't manage to type it out though

Cheers for the corrections.

So what did Jo Brand mean on QI by "probability-density function"???

The probability density function is the mathematical function which tells you where an electron is. Probably.

which sounds like what I was treading round the edges of whith my 'smeared all over the universe' bit!

to quick to post

and so I shall have to go read up on that again.