Source of cosmic rays identified

[Martin]

Paper just came out in Science magazine identifying the source of ultra high energy cosmic rays as Active Galactic Nuclei (AGN, supermassive black holes)

Excellent article on this in PHYSICS WORLD, just released today

http://physicsworld.com/cws/article/news/31764

 

 

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The actual technical article in Science magazine is "subscribers only" but there's a free summary

Science 9 November 2007:

Vol. 318. no. 5852, pp. 938 - 943

DOI: 10.1126/science.1151124

 

Using data collected at the Pierre Auger Observatory during the past 3.7 years, we demonstrated a correlation between the arrival directions of cosmic rays with energy above 6 x 10^19 electron volts and the positions of active galactic nuclei (AGN) lying within ~75 megaparsecs. ...The correlation we observed is compatible with the hypothesis that the highest-energy particles originate from nearby extragalactic sources whose flux has not been substantially reduced by interaction with the cosmic background radiation. ...

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It is interesting because the Auger observatory represents a new kind of telescope technology where you use a large piece of the atmosphere as your detector and plot the TRACKS that particles leave in the air (by Cherenkov glow, secondary neutrinos etc) and then infer back from the tracks to determine where the particle came from and how much energy

 

so you have to be watching a 3D block of atmosphere tens of kilometers thick. and be watching for these extremely brief Cherenkov glow trails and also for the shower of secondary and tertiary particles produced when the primary thing hits the air.

 

the telescope is, in a way, similar to the big 3D PARTICLE DETECTORS THEY HAVE AT COLLIDERS, like at Cern and Fermilab.

except you are using a big volume of the atmosphere as your detector chamber.

 

The concept is radically different from all telescopes since Galileo, so it's cool. and it's a significant step forward. (telescopes are humanity's eyes)

 

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the cosmic rays in question are protons going near speed of light, with kinetic energies of over 6 x 10^19 eV

which is roughly on the order of 10 joules

that is the energy you put in by lifting a one kilogram book up one meter

and the energy that makes the thump when you drop it

so one little proton has enough kinetic energy to bounce a book off the table if it could be harnessed.

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so the question was where do these very energetic protons come from and how do they get accelerated

 

and Auger team observed for 3 years and detected 20 of them

and traced each one back to an AGN

in each case it was coming from the direction of one of the known nearby (within 240 million lightyears) AGNs.

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as stuff spirals in towards a supermassive BH at center of a galaxy, the stuff heats up to plasma temperature

 

so being a plasma it is all charged particles now and it can be guided by magnetic field lines

because it is charged particles, instabilities, twisty waves, and suchlike burps of the magnetic field can throw the particles out and give them a kick.

 

so some of the plasma spiraling into the hole never reaches the event horizon and never falls in!

intead it gets accelerated out in some direction by the intense magnetic field generated by the hole.

you often see pictures of how this is imagined to look-----a spiraling glowing accretion disk, polar jets etc....

 

the actual mechanism of what accelerates the protons to make cosmic rays is still not determined

people suspect it has to do with the holes magnetic field and they have various speculations but it has not been pinned down

 

it is a step in the right direction what Auger did to confirm that the very energetic rays came from AGN

 

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turns out Norman scooped me on this. Here is his post dated 8AM this morning

 

http://www.scienceforums.net/forum/showthread.php?p=370282#post370282

[Norman Albers]

Such an accelerator! Can we see any collider physics with these suckers? Granted, collimation and luminosity are nothing to write home about. Are cross-sections low at these momenta?