- 3009 - COSMIC RAYS - and Dark Matter? When the forces of gravity and electromagnetism compete inside a giant star, eventually gravity always wins and the star collapses. So the fact that dark matter is 80% of the mass in the universe, and not 99.99999%, and regular matter is 20% as opposed to zero, strikes physicists as odd.
-------------------------------- 3009 - COSMIC RAYS - and Dark Matter?
- Cosmic rays are not rays at all but rather tiny particles cruising through the universe at nearly the speed of light. They can be made of electrons, protons or even ions of heavier elements.
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- Cosmic Rays are created in all sorts of high-energy processes throughout the universe, from supernova explosions to the mergers of stars to the final moments when gas gets sucked up by a blackhole.
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- Cosmic rays come in all sorts of energies, and generally speaking the higher-energy cosmic rays are rarer than their low-energy relatives. This relationship changes in a very slight way at a particular energy, 10^15 electron-volts, which is called the "knee."
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- The electron-volt, or eV, is just the way that particle physicists are measuring energy levels. For comparison, the most powerful particle collider on Earth, the Large Hadron Collider, can achieve 13 X 10^12 eV, which is often denoted as 13 tera electron-volts, or 13 TeV.
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- Above an energy of 10^15 eV, cosmic rays are much rarer than you would expect. This has led astronomers to believe that any cosmic rays at this energy level and higher come from outside the galaxy, while processes within the Milky Way are capable of producing cosmic rays up to and including 10^15 eV.
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- Whatever is creating these cosmic rays would be in the "peta" range of Greek prefixes, and therefore over 1,000 times more powerful than our best particle accelerators, nature. The mission is to find the source of PeV-scale cosmic rays in the Milky Way.
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- Despite their energies, it's hard to pinpoint their origins. That's because cosmic rays are made of charged particles, and charged particles traveling through interstellar space respond to our galaxy's magnetic field. Thus when you see a high-energy cosmic ray coming from a particular direction in the sky, you actually have no idea where it truly came from. Its path has bent and curved over the course of its journey to Earth.
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- Instead of hunting for cosmic rays directly, we can search for some of their relatives. When cosmic rays accidentally strike a cloud of interstellar gas, they can emit “gamma rays“, a high-energy form of radiation. These gamma rays shoot straight-line through the galaxy, allowing us to directly pinpoint their origins.
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- If we see a source of strong gamma-ray emission, we can look for nearby sources of PeV cosmic rays. This was the method employed by a team of researchers using HAWC, which is located on the Sierra Negra Volcano of south-central Mexico.
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- HAWC "stares" up at the sky with a series of tanks filled with ultra-pure water. When high-energy particles or radiation enter the tanks, they emit a flash of blue light, allowing astronomers to trace back the source onto the sky.
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- Astronomers have found a source of gamma rays exceeding 200 TeV, which could only be created by even more powerful cosmic rays — the kinds of cosmic rays that reach up into the PeV scale.
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- The source, “HAWC J1825-134“, lies roughly in the direction of the galactic center. HAWC J1825-134 appears to us as a bright blotch of gamma rays, illuminated by some unknown fount of cosmic rays. This is perhaps the most powerful known source of cosmic rays in the Milky Way.
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- A few of the usual suspect sources of high-energy cosmic rays sit within a few thousand light-years of HAWC J1825-134, but none of them can easily explain the signal. The galactic center itself is a known generator of intense cosmic ray action, but it's way too far away from HAWC J1825-134, so it has no bearing on this measurement.
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- There are some supernova remnants, and supernovae sure are powerful. But all the supernovae in the region of HAWC J1825-134 went off ages ago far too long in the past to be creating these high-energy cosmic rays now.
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- “Pulsars” are the rapidly spinning dense remnant cores of massive stars and also produce copious amounts of cosmic rays. But those too sit too far away from the source of gamma rays the energies of the electrons and protons coming off the pulsar just aren't pwerful enough to travel the thousands of light-years to the location of the gamma ray emission.
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- The source of these record-breaking cosmic rays appears to be none other than a giant “molecular cloud“. These clouds are giant, lumbering dust and gas, that roam the galaxy. They occasionally contract in on themselves and turn into stars, but otherwise they can remain cool and loose for billions of years.
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- Not causing anyone any serious threat and barely even noticeable unless you have good infrared telescopes they are the last place you would expect to find such insanely high energies.
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- Located within the cloud complex is a cluster of newborn stars, but baby stars aren't thought to be powerful enough to launch cosmic rays like this. The researchers themselves admit that they don't know how this cloud is doing it, but somehow, when nobody was paying attention, it generated some of the most powerful particles in the entire galaxy.
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- The fact that you are reading this is even more of a mystery. The most lingering mysteries of the universe is why anything exists at all.
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- That's because, in the universe today, matter and its antimatter counterpart should form in equal amounts, and then these two oppositely charged types of matter would annihilate each other on contact. So all the matter in the universe should have disappeared as soon as it formed, canceling itself out on contact with its antimatter counterpart.
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- But that didn't happen. Now, new research hypothesizes that early in the universe, there was a mysterious "kick" that produced more matter than antimatter, leading to today's imbalance. And that imbalance may have also led to the creation of “dark matter“, the mysterious substance that tugs on everything else yet doesn't interact with light.
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- We don't know what dark matter is, but it's definitely out there. It makes up about 80% of all the matter in the universe, far outweighing the stars, galaxies, dust and gas that we can see.
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- And while dark matter is certainly a heavyweight in our universe, it is, oddly, not that much of a dominating factor. In physics rarely do two competing forces come out in balance.
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- When the forces of gravity and electromagnetism compete inside a giant star, eventually gravity always wins and the star collapses. So the fact that dark matter is 80% of the mass in the universe, and not 99.99999%, and regular matter is 20% as opposed to zero, strikes physicists as odd.
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- Compounding the issue is that, as far as we know, the generation of regular matter and dark matter had absolutely nothing to do with each other. We have no clue how dark matter originated in the early universe, but whatever it was, it's currently outside the bounds of known physics.
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- And regular matter in the extremely early universe (when it was a second old), physicists suspect that regular matter was in perfect balance with antimatter (which is the same as normal matter but with an opposite electric charge).
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- We suspect this even split because we see this kind of symmetry play out today in our particle colliders, which can replicate the extreme conditions of the early universe: If you have a high-energy reaction that generates regular matter, it has an equal chance of generating antimatter instead.
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- But at some point when the universe was less than a minute old the balance between matter and antimatter shifted, and regular matter flooded the universe, relegating antimatter to obscurity.
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- On one hand, we have a massive symmetry-breaking event that led to regular matter winning over antimatter. On the other hand, we have a completely mysterious event that led to dark matter becoming the dominant, but not super dominant, form of matter in the universe.
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- Perhaps these two processes are connected, and the birth of dark matter was related to the victory of matter over antimatter. New research makes this claim by relying on something called the “baryon number symmetry“. Baryons are all of the particles made of quarks (such as protons and neutrons).
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- The symmetry simply states that the number of baryons entering an interaction must equal the number exiting it. They're allowed to change identities, but the total number must be the same. The same symmetry holds for reactions involving antiquarks.
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- This symmetry reigns in all of our experiments in the present-day universe, but it must have been violated in the early cosmos. That is how we ended up with more matter than antimatter.
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- In physics, every time a symmetry of nature gets broken, a new kind of particle, known as a "Goldstone boson," pops up to enforce the breaking of the symmetry. In the modern universe, for instance, the pion is a kind of Goldstone boson that appears when a symmetry of the strong nuclear force is broken.
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- Maybe the dark matter is a kind of Goldstone boson, associated with the breaking of baryon number symmetry in the early cosmos. The idea is called "the kick." Baryon number symmetry is never broken in our experiments, but something exciting must have happened in the early universe. It was a violent but brief event, snuffing out almost all antimatter. And whatever exotic mix of conditions happened, the baryon number symmetry broke, allowing a new Goldstone boson to appear.
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- During that singular event, the universe became flooded with dark matter particles. But then, whatever conditions that led to the symmetry breaking ended, and the universe returned to normalcy. By then, however, it was too late; the dark matter and all the rest of the matter remained.
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- After that first epic minute of the universe's history, once symmetry returned to the universe, dark matter was relegated to the shadows, never to interact with normal matter again. And the reason that there is (very roughly) the same amount of dark matter and regular matter is that they were related.
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- The new model doesn't predict the exact 80/20 split between dark and normal matter. But it does suggest the reason that dark matter and normal matter are in roughly equal balance is because they had their origins in the same event.
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- It's a very clean and intriguing idea, but it still doesn't explain exactly how that early symmetry breaking took place. But that's for another paper. One of you readers need to be working on this. ------------------------------- Other reviews available:
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- 2937 - COSMIC RAYS - where do they come from? Cosmic rays are mostly protons, the nucleus of atoms that have a positive electrical charge. They are traveling at near light speed and are entering Earth’s atmosphere and your very own body every second.
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- 2858 - COSMIC RAYS - where do they come from? Earth is being constantly bombarded from space by “cosmic rays” of an unknown origin! Mysterious cosmic rays traveling at speeds approaching that of light constantly pelt Earth’s upper atmosphere from the depths of space, creating high-energy collisions that dwarf those produced in even the most powerful particle colliders.
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- 2834 - COSMIC RAYS - The Risks of Space Travel. The scariest menace for space travelers are Cosmic Rays. They are not “rays” at all. They are charged particles that are everywhere in space hurtling at near light speed. Most are positive ions of hydrogen nuclei ( a proton, H+1 ) but some are the nuclei of the heavier elements, even iron ( Fe +26 ).
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- 2739 - COSMIC RAYS - new discoveries? - A lot of what we know about the Standard Model of Nature’s fundamental particles came from studying Cosmic Rays. All ordinary matter that we know is made of Leptons and Quarks.
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- 2729 - COSMIC RAYS - to explain an expanding Universe? Could the Universe have expanded faster than the speed of light? The Universe appears to be “homogeneous” and “isotropic“ , the same in all directions. If light really was faster in the beginning then that could explain it. One way to test this theory is to study cosmic rays.
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- 2305 - Cosmic Rays are not rays at all, they are particles, sub-atomic particles, traveling through space at nearly the speed of light. Look at your thumbnail. Now imagine that 200 cosmic ray particles traveled through your thumb nail every second. Thousands of these ‘rays” zipping through your body and through the entire Earth.
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- 1927 - Cosmic Rays, are they a curse or are they a blessing? See Review 1926 about Cosmic Rays and Planetesimals. This review continues the discussion about Cosmic Rays.
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- 1926 - To learn how Cosmic Rays may be responsible for the evolution of life on Earth.
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January 29, 2021 COSMIC RAYS - and Dark Matter ? 3009
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