Become a fan of Slashdot on Facebook

 



Forgot your password?
typodupeerror
Space Communications Earth

Most Powerful Cosmic Rays Come From Galaxies Far, Far Away (space.com) 97

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.

This discussion has been archived. No new comments can be posted.

Most Powerful Cosmic Rays Come From Galaxies Far, Far Away

Comments Filter:
  • Long long ago, far far away ... must be the tail-end of a death star beam.
    • by Tomahawk ( 1343 )

      Or the explosions from the Death Stars. After all, those things were holding on to a lot of power that had to go somewhere...

      If you look through really really really powerful telescopes would we see a planet being altered to consume the full power of a nearby sun?

      • Or the explosions from the Death Stars. After all, those things were holding on to a lot of power that had to go somewhere...

        Every Death Star contains a clone of Donald Trump in its core. When a "Fire!" command is received, the Principal Fire Command Engineer takes a lighter and pretends to put fire on Donald Trumps hair. The Death Star core bundles the concentrated anger of the Donald into a laser beam.

        This is what actually happens inside of a Death Star.

    • They are not Cosmic Rays... they're Midi-Chlorians.

    • That's ridiculous...in order to be detectible at this distance the beam would have to be incredibly coherent and collimated, like some kind of super-laser.

  • by Anonymous Coward

    Perhaps the spherical ("planetary") component of the galaxy has a large dipole magnetic field, which could cause an acceleration of charged particles which impinge upon the disc portion, thereby mimicking "intergalactic" cosmic rays.

    • by habig ( 12787 )

      The galaxy does have a magnetic field, which is rather chaotic rather than dipole shaped and weighs in at the micro-gauss level. There are a number of different ways to measure this both in our own galaxy and in other similar galaxies.

      To get charged particles of these energies (> 10^20 eV) to bend in less than a galactic radius, you need a lot more B than that, and that large a B is not seen.

  • by ytene ( 4376651 ) on Friday September 22, 2017 @03:41AM (#55242835)
    Perhaps there is another way of looking at the data.

    When dealing with astronomical observations of this type, we accept that the observations we are making could be millions or even billions of years old, based on the distance from which the phenomena originate. OK, so: old data.

    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.

    I'm not sure where Occam's Razor would swing across this story, but suspect the explanation - whatever it is - will be a simple one.
    • by Tomahawk ( 1343 )

      One issue with Occam's razor is that what may be obvious and simple to one person may not be to another. Hence 2 different people will come up with what they think to be a perfectly logical and simple explanation.

      That means that some will actually think this is Star Wars.

      I may be that person...

      • Truth be told, it satisfies both assumptions of "a long, long time ago" AND "in a galaxy far, far away".

    • by The Evil Atheist ( 2484676 ) on Friday September 22, 2017 @05:04AM (#55243045) Homepage

      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.

      • The initial energy has decayed to something like 3 kelvins nowadays, except in very small spots. However, some energetic events (quasars, at least) did happen when the Universe was younger.

    • by Roger W Moore ( 538166 ) on Friday September 22, 2017 @08:43AM (#55243571) Journal

      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.

      • by lgw ( 121541 )

        Very well put! Makes me miss the good old days of slashdot, when posts like this were more common, and the trolls were more energetic too.

      • 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.

        The obvious explanation is that they bounced off the edge of the universe, God yelled "brick!" and the rays were flung back at us via blackhole. We're part of a REALLY big game of cosmic basketball. ;)

  • by 93 Escort Wagon ( 326346 ) on Friday September 22, 2017 @03:52AM (#55242851)

    If I'm ever asked "how big is Rhode Island?", I'm going to say "it's roughly the size of the Pierre Auger Observatory in Argentina".

  • That doesn't mean they came from elsewhere, it would also sync up really well with them coming from the blackhole in the center of our galaxy and being curved back inward by the gravity of the whole galaxy - sort of a galactic-scale particle accelerator. (Like the field lines of a magnet.)
    • by ledow ( 319597 )

      If true, all such matter would have the same change / trajectory to it.

      It means they come in on a completely unexpected angle, the people studying them aren't stupid.

      Comparatively speaking the gravity of the galaxy is either pathetic, or so strong you end up caught in it's whirlpool. There's basically nothing that could ever do what you suggest, no matter how heavy or non-existent the particle (not that the mass of a particle, or absence of mass, has much to do with how much gravity affects it - gravity is

    • Re:90 Degrees (Score:5, Insightful)

      by crunchygranola ( 1954152 ) on Friday September 22, 2017 @06:24AM (#55243201)

      That doesn't mean they came from elsewhere, it would also sync up really well with them coming from the blackhole in the center of our galaxy and being curved back inward by the gravity of the whole galaxy - sort of a galactic-scale particle accelerator. (Like the field lines of a magnet.)

      Or instead of "really well", not all in any way, shape, or form. You have no idea of the physics involved, typing words is not a physical analysis.

      The galactic escape velocity for an iron atom (a typical heavy cosmic ray particle) is about 10^5 eV. All of the cosmic rays under discussion have energies greater than 10^19 eV, or 100 trillion times more energetic than the galactic escape velocity energy.

      The galactic magnetic field is much better at holding on to cosmic rays, but cannot confine them above an energy of 10^18 eV or so. Which is why the researchers are studying extragalactic cosmic rays with energies above 10^19 eV. They know these cannot be confined to the Milky Way.

      If hundreds of professional astrophysicists are devoting their careers to studying a problem, you can be sure that nothing you come up with off the top of your head, without knowing anything about the subject, is going to have any merit.

      • I think that "smack down" was a bit harsh. He's suggesting an idea -- and while I thought it had little merit, we are talking about one eV in magnitude difference between nonsense and plausible.

        Normally, it's true to assume the random person with 5 minutes of bright ideas has not thought of something that scientists who've devoted their careers to the topic. Most notably, people pointing out the sun as a heat source that climatologists may have not considered, come to mind.

        It's considered traditional to ref

    • Gravity is too weak to do this, even over long distances. The reason that nobody can detect the sources of cosmis rays is because they are easily deflected by magnetic fields and we don't have a magnetic field map of the universe to unravel this effect. Even extremely high energy rays can be deflected by weak magnetic fields due to the huge distances involved.

      So for this result, I presume that they must have ruled out the possibility that these rays are being bent back towards us by the galactic magnetic
  • How can this be new? (Score:5, Interesting)

    by aberglas ( 991072 ) on Friday September 22, 2017 @06:18AM (#55243183)

    Way, way back in the 1980s as an Honors CS student I wrote some code on an old DG Nova to analyze cosmic ray bursts for the Physics Dept (Uni Adelaide). They had several detectors, hooked into a CAMAC crate, and could measure the time difference between the receptors, and thus the direction of the burst, or at least where the cosmic ray hit the atmosphere, and by also looking at distributions work out roughly which direction the original ray came from.

    Some of them are charged particles and so do not travel in straight lines, which complicates it. I just did the programming, not much to do with the physics, but I would have thought this would be old news.

    • by Anonymous Coward

      You may be confusing two different things, the result of archaic language; Cosmic Rays are as a descriptive term as Atom Bombs once was.
      Charged Cosmic Particles, from Protons up to Iron, have been detected. That nothing heavier than Iron has been found rules out all but Stellar Fusion formation. The Bevatron was used to first characterize this, and in fact, they had an "Eye Flash" Station on top of the Shielding where one could peek at the synthetic ones. It was called "Eye Flash" due to direct Human Detect

    • by Anonymous Coward

      Hey - I was at Adelaide Uni in the 2000s. I think I learned enough to answer your question.

      All of the cosmic rays (probably) are charged particles, and do not travel in straight lines. A detector array can work out the direction a cosmic ray came from, to within about a degree, but that doesn't help much when this arrival direction could be 90 degrees away from the cosmic ray's source.

      The low-energy ones travel in very curved paths, and their arrival directions are effectively fully randomised. The high-

    • by Michael Woodhams ( 112247 ) on Friday September 22, 2017 @09:02AM (#55243649) Journal

      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.

      • by Anonymous Coward

        Oh, wow - the field's come on a bit since then! The Cherenkov telescopes operating at around 10^12 eV can now discriminate between gamma rays and cosmic rays fairly reliably, just from the shape of the shower, without needing muon counters as a discriminator. There are three big Cherenkov observatories at present - MAGIC, HESS and VERITAS - which have been very successful at mapping high-energy gamma-ray emission.

        Gamma rays do provide directional information, but only at low-ish energies (~< 10^14 eV).

    • These are much higher energy cosmic rays than those you typically detect with a couple of bits of scintillator, a few PMTs and a CAMAC crate. In addition, all you detected were the direction of one muon in the shower which the ray initiated in the atmosphere so you had very little idea of the original direction of the ray. To do that you have to reconstruct the entire shower which, for a high energy ray, is spread over a large area.
    • Isn't it fairly obvious that weak cosmic rays not coming from a nearby source must actually be strong cosmic rays if they are coming from a far away source?

  • by locofungus ( 179280 ) on Friday September 22, 2017 @06:43AM (#55243247)

    Wikipedia tells me that extreme energy cosmic rays (>5x10e19 eV) are limited to about 160 million light years.

    Trouble with astronomy is that this can be close or far depending on how you squint when you look at it :-)

    Also google the oh-my-god particle which was estimated at 3x10e20 eV.

    • Also google the oh-my-god particle which was estimated at 3x10e20 eV.

      The description I read was the energy of a baseball going forty miles an hour. We haven't found one in Bob Feller or Nolan Ryan territory yet, I guess.

  • If the most powerful cosmic rays came from our own sun, we probably wouldn't be here. DNA-based life anywhere could probably say the same.

  • by ElizabethGreene ( 1185405 ) on Friday September 22, 2017 @09:56AM (#55243881)
    I choose to believe these are the echoes of epic battles of ancient galaxy-spanning civilizations fighting to extinction over the correct pronunciation of "GIF" and whether emacs or vi is the superior editor.
    • I choose to believe these are the echoes of epic battles of ancient galaxy-spanning civilizations fighting to extinction over the correct pronunciation of "GIF" and whether emacs or vi is the superior editor.

      If they fight that hard over "GIF" it's a good job no one asked if they were iPhone or Android.

  • My father was a cosmic ray physicist, one of the top in the field. He even invented a cosmic ray "telescope: to view these events! It was called meson manner. :-) He also had a lab on top of Mount Evans in Colorado that did the same. I still have sympathies for the graduate students that had to spend a winder there!
  • by Tablizer ( 95088 ) on Friday September 22, 2017 @03:36PM (#55246463) Journal

    FTA: This direction where most of the ultra-high-energy cosmic rays came from is a place "with an increased density of nearby galaxies," Kampert added. "These galaxies, or some subset of these galaxies, contain the sources of these cosmic rays."

    They are probably from "nearby galaxies" based on the direction clustering. This would also imply the rays dissipate or weaken over distance, or else their source should appear roughly uniform across the sky, because "lasting" rays would otherwise be arriving from galaxies all over the universe in all directions. Although red-shifting (expansion) may also account for some distance-based weakening. Magnetic fields, ions, and dust in stuff in between could also weaken the rays over time. The cause(s) of the weakening is only speculative at this time.

You see but you do not observe. Sir Arthur Conan Doyle, in "The Memoirs of Sherlock Holmes"

Working...