Most Powerful Cosmic Rays Come From Galaxies Far, Far Away (space.com)

A new study finds the highest-energy cosmic rays to bombard Earth come from galaxies far, far away. Space.com reports: The sun emits relatively low-energy cosmic rays. However, for more than 50 years, scientists have also detected ultra-high-energy cosmic rays, ones far beyond the capability of any particle accelerator on Earth to generate. One way to discover the origins of ultra-high-energy cosmic rays is to study their directions of travel. However, ultra-high-energy cosmic rays only rarely strike Earth's atmosphere, with one hitting any given area about the size of a soccer field about once per century, the researchers said. In order to detect ultra-high-energy cosmic rays, scientists look for the spray of electrons, photons and other particles that result when ultra-high-energy cosmic rays hit the top of Earth's atmosphere. Each of these showers contains more than 10 billion particles, which fly downward in a disk shaped like a giant plate miles wide, according to the statement. Scientists examined the sprays from ultra-high-energy cosmic rays using the largest cosmic-ray observatory yet: the Pierre Auger Observatory built in the western plains of Argentina in 2001. It consists of an array of 1,600 particle detectors deployed in a hexagonal grid over 1,160 square miles (3,000 square kilometers), an area comparable in size to Rhode Island. A connected set of telescopes is also used to see the dim fluorescent light the particles in the sprays emit at night.

The researchers analyzed data collected between 2004 and 2016. During these 12 years, the scientists detected more than 30,000 ultra-high-energy cosmic rays. If ultra-high-energy cosmic rays came from the Milky Way, one might perhaps expect them to come from all across the sky, or perhaps mostly from the direction of the supermassive black hole at the galaxy's center. However, the researchers saw that ultra-high-energy cosmic rays mostly came from a broad area of sky about 90 degrees away from the direction of the Milky Way's core.

Comments

Re:Not the Distance, but the Time...

[The Evil Atheist]

We are also told by physicists that our universe started with a "big bang", a state and point in time at which the state of our universe was so energised that the sub-atomic particles we take for granted today [never mind atoms and molecules] did not exist - because the universe had not cooled sufficiently. So if you extrapolate this facts, don't they suggest that it stands to reason that, the further away in distance [and thus the further back in time] that we look, the higher the energies we would expect to observe. Everything else is [just / subject to] entropy.

No, because the high energies from that time has cooled down to what we predicted and observed as the Cosmic Microwave Background.

Re:PROOF that evolution is a HOAX.

[Anonymous Coward]

Human like footprints have been found that are over 6 million years old. To record history you have to be able to write.

Yes, but can't explain Cosmic Rays

[Roger W Moore]

So if you extrapolate this facts, don't they suggest that it stands to reason that, the further away in distance [and thus the further back in time] that we look, the higher the energies we would expect to observe.

To get to the energies of cosmic rays you have to go back to before 10^-13 s after the Big Bang. Back then the Universe was incredibly small and incredibly dense. So dense and energetic that everything, even things like neutrinos, were colliding and interacting with everything around them. This meant that everything was roughly in thermal equilibrium and had comparable energies.

By the time than the charged particles responsible for cosmic rays the energy and density of the universe would have been much, much lower since it would require photons to decouple first which happened 380,000 years after the Big Bang. The result is that there is no way that a Cosmic ray, as a charged particle, can get its energy directly from the Big Bang.

It could get it indirectly if there were some high mass, exotic and as yet undiscovered particle which was created in the Big Bang and which decays with a lifetime of billions of years or which might annihilate with itself to create these particles. This is one possible way to detect Dark Matter but it is extremely unlikely (impossible without even more new physics) that this would provide enough energy to explain high energy cosmic rays.

Re:How can this be new?

[Michael Woodhams]

I did my MSc across the Tasman in New Zealand in 1988 on the JANZOS cosmic ray experiment. We had Cerenkov telescopes detecting particles of about 10^12 eV, and particle detectors for showers from primary particles of about 10^15 eV. (i.e. high enough energy that the cosmic ray shower reached ground level.)

We were well aware of the problem of charged particles traveling straight. A few cosmic rays (from memory, about 1%) are gamma rays, which do travel straight. The problem is that we couldn't tell from the shower whether the primary particle was a gamma ray, so you're looking for a directional signal of 1% against a background noise of 99%.

There were suggestions at the time that Cerenkov telescopes with better imaging than ours could perhaps distinguish gamma ray induced showers, and for the higher energy showers you could use underground muon detectors, because hadron-triggered showers produced more muons. I haven't followed cosmic ray astronomy since then, so I don't know the current state of the art. I found it frustrating to be in a field where you struggle to convince others (and possibly yourself) that you've seen anything at all other than noise.

The AC from Adelaide in the 2000s replying to your message says that at these super-high energies you can get direction information because they are too high energy to be deflected much. It makes sense that this would be the case at sufficiently high energy, although I don't know what 'sufficiently high energy' would be.

I did maximum likelihood analysis on reconstructing the direction of the cosmic rays from the particle detectors. I had a little legacy code to start with, which was in Fortran 77, so that is what I used. Happily, I have never had to use Fortran ever again.