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Why? It captures information from a flux of particles (not photons, but neutrinos in this case) emitted by astrophysical objects. It allows us to study properties of those objects (and of the detected particles as well). It doesn't have a resolution high enough to give us an "image" of most of those objects, but Hubble can't image most single stars too. IceCube won't give you a pretty picture for APOD, but it will do everything else we can do with an optical telescope, or a charged particle telescope such as Auger.

It is much more complex than that. The flux of 10^20 eV particles has NOT increased it is still very very low (like 1 per 100km^2 per century). Check out the Auger Southern observatory site for some info on those particles. What is being discussed in this article is much lower energies. These cause damage only as a side effect and virtually all space mission will not be effected by them. What can happen is that electronics which are not radiation hardened can be put into a funky state by the passage of a charged particle through a sensitive portion of the electronics causing a fault which could be unrecoverable. All NASA missions require radiation hardened electronics for any mission critical components and are thus much less likely to fail due to interactions with cosmic rays.

More info on Auger can be found here.

Looking at the cosmic ray particle spectrum (google 'cosmic ray spectrum') one can see stuff at 10^20 eV, that is a lot higher energy than the couple of TeV these particle accelerators achieve (no mean feat). Here's a list of some observatories that look at cosmic rays:

Pierre Auger Observatory : http://www.auger.org/index.html
HESS : http://www.mpi-hd.mpg.de/hfm/HESS/
MAGIC : http://magic.mppmu.mpg.de/
Icecube http://icecube.wisc.edu/

The LHC (http://en.wikipedia.org/wiki/Lhc) has a collison energy of in the TeV scale (tera = 10^12)

The Pierre Auger Observatory (http://www.auger.org/observatory/) records one 10^19 eV hit per km^2 a year, just on earth. If that hasn't turned up any major anomalies in our solar system or even in the major mass centers in our close vicinity over the billions of years it's been happening then I would like an explantion why.

It is not merely about the "same energy". It is about: the exact same combination of conditions as will exist within the LHC.

At the individual particle scale, energy all that matters here. Space is mostly empty, whether you're a few blasts of protons smacking into each other in a pretty good vacuum in the LHC or individual ones from outer space hitting nuclei in the Earth's upper atmosphere. Really, it makes no difference. Not just theory, thousands of rather smart people have been building clever devices to watch this stuff happen for decades, and it all adds up.

You might say "but the basic laws of physics might fall apart just past where you've carefully studied so far. Ok, unlikely, but they might. However, everything we've seen by watching what flies of cosmic ray collisions across the whole range of energies above where we've well-studied the things is very consistent with what we know from lower energy ones. It's the fine detail we're missing, not the basics.

Please show me where on Earth I would find the natural combination of conditions that are the same as will exist within the operational LHC.

No need to buy a ticket. Sit back and look up. The LHC center of mass energy is about the same as the average collision which creates the cosmic ray muon showers I see every couple of seconds in the MINOS Far Detector. Here, look for yourself. And these are garden variety things compared the the more rare and far more energetic ones we've observed in really big arrays designed specifically to go count how many we get of each one, like this experiment.

By "object", I mean "astrophysical object." Heck, you can have relativistic dust grains in the vicinity of black holes, but I'm pretty sure that nowhere in the known Universe are you going to find a star passing by another star at near the speed of light.

Given that the experiment I work on is the Pierre Auger Observatory, I'm quite familiar with the 320 EeV particle.

Not that you have to go to 320 EeV to get a 0.577 c speed. For a proton, that's a Lorentz factor of ~1.15, which is an energy in the GeV range. That's nothing.

I've read (somewhere) that the highest energy *photon* ever observed was ~1MJ. That is on the order of 10^24eV! Not sure of the error on this though.

As for highest energy cosmic rays, well, they seem to get to 10^20eV. But there is a cutoff limit for cosmic rays since they interact with microwave background (see that same page).

But we *have*; and given the repeated observations...regardless of the curve, there will *still* be some particles at the extreme ends. Given that our detectors are still fairly primitive, it's possible that the high-e events are statistically more likely to be detected, is it not?


(Yes, I know we've seen them. Otherwise I'd be in a different field right now, and the waiters in Malargue, Argentina wouldn't all know me by name. :) But the fact that we've seen them probably implies that we don't know the source, not that we don't understand the propagation.)

I think you're missing what I'm saying - the only way we could've seen any of these particles is if they came from less than 50 Mpc. The GZK effect gets much, much stronger as you go to higher energies. After 50 Mpc, a particle that starts off at 1E21 is below 6E19. Same with particles of higher energy. Astrophysically, that's right in our backyard. There's nothing we know of that could accelerate particles like that. There's an additional problem, which is the fact that there's a spectral change in the 10^19 range that we can't explain, either. Spectral changes occur when acceleration mechanisms change. Supernovae fall apart in the 10^14-10^15 range, and there's a spectral change there, too. The fact that the spectrum continues after 10^19 (in fact, it flattens) implies that there's a new source that's "turning on" in that energy range.

As far as I understand it, the mw background is the peak energy distribution, not the total one. It's what we built our detectors to observe because it's easiest to observe - sorting random noise from the detector noise in gamma/XR is damned difficult.

It's a pure blackbody distribution, with a characteristic temperature at 2.7K. In order to have a particle out of that spectrum at 10^20, it would need to have about 10^23 times the most probable value. I haven't done the math, I'll admit - but something like e^-(10^23) probably times even the size of the Universe probably doesn't even equal *1*. (Oddly enough e^(-(10^23)) times the *number of bits* in the Universe through the end of Time wouldn't even be 1)

We don't know that, because we don't have a source for those protons. Sure, there's nothing on that vector, but even ultra-high-c factor particle paths can be altered by gravitational fields - which were not mentioned in the OMG webpage)

Yes, we do. The GZK cutoff is not "experimental physics". It's the delta++ resonance. This is stuff that they did in the 1950s, and has been extremely well studied since then. It's just proton-photon interactions. Unless Lorentz invariance is wrong (which is possible! but you should read the paper on that suggestion, and it's very, very bad), we know that GZK will slow a particle travelling faster than 6E19 couldn't've travelled more than 50 Mpc.

And gravity doesn't alter particle's paths anywhere near as much as magnetic fields do, and those particles have such high speed that neither gravity, magnetic fields, or anything else could possibly alter their path more than a tenth of a degree.

The "OMG particle"'s webpage (which, by the way, I've never heard it called - which is... odd) is a little sparse. Try the Auger homepage, this UNM site, or this LSU site. If you've got access to Science magazine, also here.

There are actually many, many more interesting things going on in the UHECR field which I haven't even mentioned.

Natural cosmic ray (probably created by supernovae or hypernovae) are far more energetic than any puny little collision we can muster.

First off, the origin of 10^20 eV cosmics is not at all understood. The Auger experiment for example is investigating this question.

Second, those very high energetic cosmic particles crash into earth (or whatever object in their path), which is basically at rest (compared to the speed of the cosmics). In particle physics, this is called "fixed target mode". Since both energy and momentum are conserved in the crash, the particles produced in the collision are not at rest but must carry the momentum of the cosmics (think billard). Thus, only a small part of the energy of the cosmics is avalable for forming new objects, namely sqrt(E), which is only 10 GeV, well within range of terrestral accelerators since over 10 years. The rest of the cosmics' energy just propels the new objects.

The Large Hadron Collider at CERN will crash protons at 7 TeV energy against other protons of the same energy/speed but opposite direction. This is called "collider mode", and the entire energy of 2x7=14 TeV is available for new objects.

(Well, not really, since protons are themselves compound objects, made of 3 quarks and lots of "gluons" which glue the quarks together. So really its only a quark-quark or gluon-gluon collision with less than a sixth of 14 TeV but still more than the 10 GeV above.)

There is of course the possibility of a cosmic particle colliding with another cosmic particle, but given the rate of 5 of those cosmics per 1000 km^2 per year, and the very low cross section of these high energetic particles, this isn't going to happen very often :-)

Oh my God, I'm amazed - this is the observatory I actually WORK for, and it's on SLASHDOT, my God.

Forgive me for going completely crazy replying to everyone, but this is just too cool.

OK, so long as people promise not to Slashdot the server (heh, that was dumb) for anyone who wants more information, go to the main Auger website, or for even cooler information, go to the Auger site in Argentina.

Auger is actually a very interesting project, and it's not like anything you'd ever think of - it's a 1600 km^2 array of water Cerenkov detectors (10 cubic meters of water) spaced 1.5 km apart - the picture in the article is of the flourescence detector, which is more like what you think of for a standard detector, but due to the limitations of the flourescence method of detecting cosmic rays, its duty time is only 10%, as opposed to the 100% of the surface array.

The project is proceeding along... pretty well. We've basically finished the Engineering Array, a small-scale testbed to find all of the design flaws in the initial project (and boy, did we find them) and we've detected some cosmic rays which we believe to be ~10^19 eV. We've also demonstrated the hybrid design as well (events where the flourescence detector triggers as well as the surface detector).

The black hole stuff isn't the important goal of the project - the goal is to elucidate the spectrum of cosmic rays above 10^20 eV, because we have no idea where those particles come from - all of basic physics says they can't exist. This is one of the big questions in astrophysics in recent years, up there with gamma ray bursts and odd quantum states of matter.

It's way cool. And not just because I work on it...

Many physicists now argue we cannot experience these extra dimensions directly because they became rolled up more tightly than the width of a single atom during the Big Bang.

There's more information about the Pierre Auger Project here.

In the 1960's, a ground array of 19 detectors spread over 8 square kilometers was built at Volcano Ranch, New Mexico, by a team led by John Linsley. In 1963, his team reported an observation of a cosmic ray with an energy greater than 10^20 eV. Since then, several large detector arrays have been built to search for very high energy csomic rays. One such detector, called the Fly's Eye, and built in the Utah desert, observed a cosmic ray shower in 1991 that at its maximum contained 200 billion particles in the shower. The energy of the primary particle was 3 x 10^20 eV, the highest energy cosmic ray ever observed. While the composition of the primary particle isn't known with certain, the best guess is that it was a moderate mass nucleus (something like oxygen).

Mother of god, a trillion electron volts thru a pair of sport sandals? That can't be good for my feet!

While I'm sure it kicks the ass of the tree-hugging Birkatron, I have to believe that something like the Nikatron will eventually replace it due to reduced, off-shore labour costs.

The question of exactly where all of these insanely high energy particle come from is a deep mystery. Proposed answers include: Gamma Ray Bursts, Active Galactic Nuclei, interactions involving Magnetic Monopoles or Cosmic Strings, the decays of super-massive relics from the big bang, etc. For more info on these rare events, see the Pierre Auger Observatory website at www.auger.org.

Now 2.5*10^7 TeV sounds like an incredible ammount of energy compared to the .1 TeV/nucleon of RHIC, but since the cosmic rays are hitting essentially stationary nuclei in the Earth's atmosphere as opposed to the head-on collisions of RHIC, most of the energy just goes into the kinetic energy of the collision debris rather than into producing interesting physics. The relevant figure is the center of mass energy of the cosmic ray and target nucleus system. It turns out that this is equal to sqrt(2*m*E), where m is the mass of the target and E is the mass of the cosmic ray. Supposing that the target is a Nitrogen nucleus, we get sqrt(2*.014 TeV*2.5*10^7 TeV) or roughly 10^6 TeV. The corresponding figure for RHIC 2*(200 nucleons)*(100 GeV/nucleon)=4*10^4 TeV. The cosmic ray events win, but only by a bit more than an order of magnitude. (Note that this is all very much "back of the napkin" calculation, and may not be exactly right, but it's close.)

That was fun, but what does it all mean? Well, from the RHIC documentation, I figure that RHIC will have roughly 10^15 bunch crossings in each full year of collision running. Assuming that there is less than one collision per beam crossing (it makes it much easier to figure out what's going on in each collision), RHIC will produce an order of magnitude fewer collisions, with an order of magnitude lower energy density than these cosmic rays that bombard the Earth naturally. While a more careful analysis may change some of these numbers by a bit, it seems pretty unlikely that RHIC will destroy the Earth, when all of these cosmic ray collisions obviously haven't.