- 3283 - COSMIC RAYS - a lot we don’t know? Great mysteries of the universe surround us, all the time. They even permeate us, sailing straight through our bodies. One such mystery is “cosmic rays“, made of tiny bits of atoms. These rays, which are not “rays” but particles, are passing through us at this very moment, are not harmful to us or any other life on the surface of Earth, we think.
--------------------- 3283 - COSMIC RAYS - a lot we don’t know?
- Some of these Cosmic Ray particles carry so much energy that physicists are baffled by what object in the universe could have created them. Many are much too powerful to have originated from our sun. Many are even much too powerful to have originated from an exploding star.
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- Because cosmic rays don’t often travel in a straight line, we don’t even know where in the night sky they are coming from. The answer to the mystery of cosmic rays could involve objects and physical phenomena in the universe that no one has ever seen or recorded before.
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- Though we don’t know where cosmic rays come from, or how they get here, we can see what happens when these cosmic rays hit our planet’s atmosphere at nearly the speed of light.
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- When the particles in cosmic rays collide with the atoms at the top of the atmosphere, they burst, tearing apart atmospheric atoms in a violent collision. The particles from that explosion then keep bursting apart other bits of matter, in a snowballing chain reaction. Some of this atomic shrapnel even hits the ground.
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- It’s possible to see this in action by building what’s called a cloud chamber out of a glass jar, felt, dry ice, and isopropyl alcohol (i.e. rubbing alcohol). You soak the felt in the alcohol, and the dry ice (which is super-cold solid carbon dioxide) cools down the alcohol vapor, which is streaming down from the felt. That creates a cloud of alcohol vapor.
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- In this chamber, you can see the cosmic rays, particularly those from a particle called a muon. Muons are like electrons, but a bit heavier. Every square centimeter of Earth at sea level, including the space at the top of your head, gets hit by one muon every minute.
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- Like electrons, muons carry a negative charge. When the muons zip through the alcohol cloud, they ionize (charge) the air they pass through. The charge in the air attracts the alcohol vapor, and it condenses into droplets. And those droplets then trace the path the cosmic rays made through the cloud chamber.
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- When you see the paths these muons make these subatomic particles rocket down to Earth at 98 percent the speed of light, over 650,000,000 miles per hour.
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- Cosmic Rays are moving so fast, they experience the time dilation predicted by Einstein’s theory of special relativity. They are supposed to decay, break apart into smaller components, electrons, and neutrinos, in just 2.2 microseconds, which would mean they’d barely get 2,000 feet down from the top of the atmosphere before dying.
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- But because they’re moving so fast, relative to us, they age 22 times more slowly. If Einstein’s theory weren’t true, we wouldn’t see any muons in the cloud chamber.
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- Our theoretical physicist colleagues are perplexed” about how these particles are energized. They can’t figure out where they are coming from.
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- This mystery of cosmic rays began with their discovery in 1912. Victor Hess took a ride on a hot air balloon and discovered the amount of radiation in the atmosphere increases the higher up you go.
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- He was on the balloon to isolate his experiment from radiation. But it was only noisier higher up. That led him to conclude that the radiation was coming from space, and not radioactivity from rocks in the earth.
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- He also took this balloon ride during a total solar eclipse. With the moon blocking the sun, cosmic radiation coming from the sun ought to have been filtered out. But he still recorded some. That led him to the insight that the radiation was not coming from the sun, but from deeper in space.
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- The highest-energy cosmic ray particle ever recorded, the “Oh-My-God” particle, was some 2,000,000 times more energetic than the most energetic proton propelled by the Large Hadron Collider, the world’s most powerful particle accelerator.
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- Nobody knows what in the universe is able to give a subatomic particle such an energy. Scientists are baffled to know such a particle can even reach Earth. Particles with such high energies are thought to interact with the radiation leftover from the Big Bang and the creation of the universe, which ought to put the breaks on them before they reach us.
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- What created the “Oh-My-God” particle and these powerful cosmic rays is a complete, baffling mystery. Astronomers do know some cosmic rays come from the sun. But the strongest ones, the most mysterious ones, come from the great way-out-there in the galaxy and universe.
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- The problem with looking for the sources of these very high energy cosmic rays is that the rays don’t always travel in a straight line. The various magnetic fields of the galaxy and universe deflect them, and put them on bending paths.
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- Many of the cosmic rays that hit Earth, particularly the ones that come from our sun, get deflected to the poles due to Earth’s magnetic field. That’s why we have the Northern and Southern Lights near the poles.
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- There are a few huge projects underway to better understand where these cosmic rays come from. An enormous block of ice at the South Pole is a giant cosmic-ray detector
Science has built the “IceCube Neutrino Observatory“, forged directly into the ice beneath the surface of the South Pole.
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- It is a 1-cubic kilometer, or, 1.3 billion cubic yards, block of crystal-clear ice surrounded by sensors. These sensors are set up to detect when subatomic particles called neutrinos, which travel along with other subatomic particles in cosmic rays, crash into Earth.
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- Neutrinos are different from the other components of cosmic rays in one really important way: They don’t interact with other forms of matter much at all. They don’t have any electrical charge. That means they travel through the universe in a relatively straight line, and we can trace them back to a source.
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- Every once in a while a neutrino, perhaps every one in 100,000, will hit an atom in the ice at the observatory and break the atom apart. This collision produces other subatomic particles, which are then propelled to a speed faster than the speed of light as they pass through the ice.
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- You might have heard that nothing can travel faster than light. That’s true, but only in a vacuum. The photons that make up light actually slow down a bit when they enter a dense substance like ice. But other subatomic particles, like muons and electrons, do not slow down.
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- When particles are moving faster than light through a medium like ice, they glow. It’s called “Cherenkov radiation“. And the phenomenon is similar to that of a sonic boom. When particles move faster than light, they leave wakes of an eerie blue light like a speedboat leaves wakes in the water.
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- The “Pierre Auger Observatory” uses an array of 1,600 tanks, each filled with 3,000 gallons of water. The tanks are spread across more than 1,000 square miles in Mendoza, Argentina.
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- The tanks work like the block of ice at the South Pole. But instead of using ice to record cosmic rays, they use water. The tanks are completely pitch black inside. But when cosmic rays, more than just neutrinos, enter the tanks, they cause little bursts of light, via Cherenkov radiation, as they exceed the speed of light in water.
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- If many of the tanks record a burst of cosmic rays at the same time, the scientists can then work backward and figure out the energy of the particle that hit at the top of the atmosphere. They can also make a rough guess on where in the sky the particle was shot from.
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- In the Northern Hemisphere, there’s a similar experiment in Utah called the “telescope array“. Like the tanks in South America, the array in Utah has a series of detectors spread out over an enormous area. Currently, it takes up about 300 square miles, but there’s an upgrade in the works expanding it up to 1,200 square miles.
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- The detectors in Utah are made up of super-clear acrylic plastic, and are housed in units that kind of look like hospital beds. If many of the detectors record a hit in sequence astronomers can reconstruct the direction from which they came.
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- Every square kilometer of Earth only sees about one of these high energy particles per century. And to account for the fact that these rays don’t often travel in a straight line, it’s going to take a mountain of data.
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- The Pierre Auger observatory has some data that some of these high-energy particles come from starburst galaxies, which are galaxies that are forming stars at a very fast rate. About a quarter of the most powerful cosmic rays observed come from a circle about 6 percent the size of the night sky, near the Big Dipper constellation.
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- Last summer, 2020, scientists at the IceCube observatory published exciting evidence that galaxies called “blazars” generate some of these high-energy particles. Blazars have supermassive blackholes at the center of them that rip apart matter into its constituent parts, and then blast subatomic particles off like a laser cannon into space.
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- Smartphone cameras work because photons, the subatomic particle that constitute light, activates a sensor at the back of the lens. Cosmic rays can activate the sensor too. Every once in a while a cosmic ray can interfere with a microprocessor and cause a computer to crash.
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- If you put your phone camera face down, most of the light is blocked, and you’d get a black picture. But, particles from space, will pass right through your phone, ceiling, or wall, and hit the camera sensor, and will leave a trace.
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- The hope is that millions of users can turn the app on at night while they are asleep, and it will look for these cosmic rays. With enough phones astronomers can get a better picture of where cosmic rays come from.
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- The existence of high-energy cosmic rays tells us our understanding of the universe is woefully incomplete.
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- September 20, 2021 COSMIC RAYS - a lot we don’t know? 3283
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