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Cosmic Rays From Galactic Black Holes
dork writes in with word of a study that contradicts, at least for the highest-energy events, the recent conclusion that cosmic rays are probably formed in supernova remnants. The Pierre Auger Observatory in Argentina has announced that active galactic nuclei are the most likely candidates for the source of the highest-energy cosmic rays that hit Earth. The researchers found that the sources of these highly energetic events are not distributed uniformly across the sky, linking their origins to the locations of nearby galaxies hosting active nuclei in their centers. These galaxies are thought to be powered by supermassive black holes that are devouring large amounts of matter. The exact mechanism of how particles get accelerated to energies 100 million times higher than achievable by the most powerful particle accelerators on Earth is still unknown. The observatory has made 1% of its events available through a public online event display."
The energies of these cosmic rays are measure in EeV (exa-electron volts). 1 EeV ~ 0.16J The most common ones are sitting at around 35 EeV. 35EeV * 0.16J/EeV = 5.6J By comparison, g=9.8 m/s^2. So the weight of a 1 Kg block is 9.8N. Now to lift an object a height h work=mg*h. So, h=work/mg. Puting is 5.6J for the work we get h=5.6/9.5=0.57m So, these photons have enough energy lift a 1 kg block over a half a meter!
The GZK cut-off prevents such highly energetic particles from reaching the Earth unless they are formed in our galactic neighborhood, so this article only talks about how these particles may have formed, but does not answer why it is that they still have their high energies when they reach us.
I was reading about these particles the other day when I got trapped
in an endless Wikipedia link chain. (Damn you and your font of
interesting information!) Anyway, I'm mostly including it because I
was vastly amused by the nickname they gave the particles.
http://en.wikipedia.org/wiki/Oh_my_god_particle
There is not really a contradiction between the results demonstrating that supernova remnants (SNR) in our Galaxy are the source of cosmic-rays and this result (suggesting that active galaxies (AGN) are the source). Both are likely correct: that SNR are the source of the lower energy cosmic-rays and that AGN are the source of the ultra-high energy cosmic-rays.
It had always been expected that the lower and higher energy cosmic-rays would have different origins. At lower energies, the magnetic fields in SNR are strong enough that the charged particles are magnetically trapped and rattle around inside the SNR continuing to be accelerated to higher and higher energies in the process. Once they attain a high enough energy, they are no longer contained in the SNR and escape (and thus do not gain more energy). The very high-energy cosmic-rays seen by Auger are much more energetic than anything in our Galaxy can produce. Active galaxies, which are known to accelerate particles very efficiently fueled by the accretion of matter onto a supermassive black hole had always been a leading candidate for the sources of the ultra high energy cosmic-rays. It is an outstanding result.