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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."
> So why dont they use it to gather data ?
They do.
Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.
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.
Cosmic rays can provide some interesting information for physicists.
In fact, since the particle accelerator for the LHC has not yet turned on, the only real "data" to speak of is cosmic rays passing through the detectors. It's great background noise to make sure everything is working.
However, it's not as good as an accelerator for a couple of reasons:
1) Most interesting particles are the decay products of a collision, not necessarily in cosmic rays.
2) Repeatability. While protons in the LHC may collide at 100Hz or so, cosmic rays are a little less predictable.
3) Statistics. To show the existence of a new particle, you need statistics at 5-sigma. This might require tens or hundreds of thousands of recorded events of a certain signature in order to be considered reliable. You simply can't get that from cosmic rays.
(3) is why some results from the Tevatron are just now getting interesting - the device has simply been running long enough to make the discovery of the Higgs a remote possibility because of the sheer number of days running and events recorded. Because the energies of the LHC are going to be much higher and at a greater rate, the Higgs search should be much faster on that machine.
(I am not a particle physicist. I just work for them.)
Most interesting particles are the decay products of a collision, not necessarily in cosmic rays.
The problem here is one of energy. Cosmic rays do actually "collide" with the ATLAS detector but the energy available is far, far lower than current colliders plus most of the cosmic rays are muons which mean that they only rarely have a real collision.
Repeatability. While protons in the LHC may collide at 100Hz or so, cosmic rays are a little less predictable.
You are a few orders of magnitude off here. The LHC proton bunches collide at 40MHz and there are roughly 20 collisions per crossing at nominal intensity. In fact the bunches collide so rapidly that the particles from the preceding collision have not actually escaped the detector by the time the next bunch crossing occurs. On the other had, at the surface, one cosmic ray will pass through 1cm3 every second. Down in the detector pit this is less but what also kills the rate is that we want a direction that will pass through most of the detector.
Statistics. To show the existence of a new particle, you need statistics at 5-sigma. This might require tens or hundreds of thousands of recorded events of a certain signature in order to be considered reliable. You simply can't get that from cosmic rays.
Actually new particles have been found in cosmic rays - that is how the muon (heavier brother of the electron) was discovered in 1935/6 (IIRC). To get to 5-sigma you simply need a lot more signal events than background events. If your backgrounds are very low then you don't need many events at all.
(I am not a particle physicist. I just work for them.)
I am a particle physicist and while I don't know whom you work for or in what capacity - thanks! A lot of people don't realise that while there are a lot of physicists working on theses experiments there are even more technicians, engineers, machine operators etc. behind the scenes making it all possible.