Black holes event horizon

arwhiston · Jan 13, 2005

Newbie here wants to know if black holes at their event horizon on inward are so dense that nothing not even light escapes, how can xrays be shooting out the north and south pole like recent news story?

nacnud · Jan 13, 2005

er... Hawking radiation [wikipedia.org] is formed at, well slightly outside, the event horizon. The distribution of matter inside the even horizon is lightly to be clumped together in the centre of the black hole. There is not a physical boundary as you cross the event horizon but the gravitational gradient would pull you apart long before you reached the surface.

Saiph · Jan 13, 2005

Right, what you see emitted "from" the BH is actually emitted in close proximity to it. It's poor use of the language by the media (and quite likely astronomers talking to the media). So material near the BH emit's x-rays. This material is funneled up via magnetic fields to the poles, and so the X-rays tend to be emitted from the poles, or parrallel to the poles. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

claywoman · Jan 13, 2005

please forgive the questioning of a real newbie here, but, okay what you are saying is that the X-rays are emited outside the hole itself? could it be that the X-rays are the last 'screams' of the planet(s) as they are consumed by the hole itself?

Saiph · Jan 13, 2005

I wouldn't call it screams, but yeah. As the matter enters a BH, it gets accelerated. As such, if it's charged (and it usually is for various reasons) it emits light. Since the acceleration near a BH is extreme, the light emitted is of higher energies (x-rays). Anyway, off to my galactic astronomy class. P.s. don't worry about being a newb and asking questions. Everyone's been a newb, and questions are good, from anybody, at any time, for any reason. So ask away! <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

nacnud · Jan 13, 2005

I think I confused things with the Hawking radiation thing. When material is falling into the hole it forms an accretion disk around the hole a bit like Saturn’s rings. As this material falls it accelerates and bumps into itself heating it up. Some of this material and associated x-ray is accelerated into jets and emitted from the poles by the black holes magnetic field before it reaches the event horizon. Only black holes that have material falling into them emit x-ray jets. The X-rays from Hawking radiation are property of the black hole, it always emits these even when material is not falling into it, well if you discount the virtual photons that create the radiation <img src="/images/icons/smile.gif" />. However this Hawking radiation is much much weaker that the jets, almost negligible.

nacnud · Jan 13, 2005

Yup, you’re right. It has been along time since I properly thought about it but I forgot that there was a relationship between the black hole size and the most frequently absorbed virtual photon. I only remembered that small black holes evaporate in a puff of X-rays, oops.

Saiph · Jan 13, 2005

well, for supermassive BH's it's possible to cross the EH intact, though very uncomfortable, before the tidal stresses rip you apart. Now, standard stellar BH's though, and you're toast before you cross it. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

Saiph · Jan 13, 2005

<img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

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