If I had a neutrino flashlight, that stream of neutrinos would go through the wall. But every once in a while a neutrino — perhaps every one in , — will hit an atom in the ice at the observatory and break the atom apart.
Then something spectacular happens: The collision produces other subatomic particles, which are then propelled to a speed faster than the speed of light as they pass through the ice. You might have heard that nothing can travel faster than light. The photons that make up light a subatomic particle in their own right 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.
When particles are moving faster than light through a medium like ice, they glow. And the phenomenon is similar to that of a sonic boom. When you go faster than the speed of sound, you produce a blast of noise. When particles move faster than light, they leave wakes of an eerie blue light like a speedboat leaves wakes in the water. The neutrino is the tear-drop shape in gray.
The Pierre Auger Observatory , where Castellina works, uses an array of 1, tanks, each filled with 3, gallons of water.
The tanks are spread across more than 1, square miles in Mendoza, Argentina. 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.
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. Like the tanks in South America, the array in Utah has a series of detectors spread out over an enormous area.
The larger the area, the greater the chance to spot the most elusive and powerful cosmic rays. The detectors in Utah are made up of super-clear acrylic plastic, and are housed in units that kind of look like hospital beds. The observatory can also do something cool. On very clear, dark nights in the Utah desert, it can actually see the faint trails of cosmic rays lighting up in our atmosphere.
With enough data on these high-energy cosmic rays, scientists hope to one day better pinpoint where in the sky they come from. But already, we have some clues. The Pierre Auger observatory has some not yet conclusive data that some of these high-energy particles come from starburst galaxies, which are galaxies that are forming stars at a very fast rate.
More clues continue to trickle in. Last summer, scientists at the IceCube observatory published exciting evidence that galaxies called blazars generate some of these high-energy particles. Blazars have supermassive black holes 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. They also need to be repeated. It could be aliens, but I doubt it. What scientists need is more data, more observations to be able to pinpoint the sources in the sky these particles are coming from.
And soon, you can get in on the search. Your phone can be turned into a cosmic ray detector. Daniel Whiteson is a physicist at the University of California Irvine who has been working on a crowd-sourced cosmic ray project. The camera in your phone works because photons — the subatomic particle that constitute light — activates a sensor at the back of the lens.
Cosmic rays can activate the sensor too. It was on such balloon flights that Hess discovered cosmic rays. Cosmic rays are mostly high-speed atomic nuclei and electrons. A positively charged particle with the mass of an electron is called a positron and is a form of antimatter we discussed antimatter in The Sun: A Nuclear Powerhouse. The abundances of various atomic nuclei in cosmic rays mirror the abundances in stars and interstellar gas, with one important exception.
The light elements lithium, beryllium, and boron are far more abundant in cosmic rays than in the Sun and stars. These light elements are formed when high-speed, cosmic-ray nuclei of carbon, nitrogen, and oxygen collide with protons in interstellar space and break apart. By the way, if you, like most readers, have not memorized all the elements and want to see how any of those we mention fit into the sequence of elements, you will find them all listed in Appendix K in order of the number of protons they contain.
Cosmic rays reach Earth in substantial numbers, and we can determine their properties either by capturing them directly or by observing the reactions that occur when they collide with atoms in our atmosphere.
Some of the cosmic rays come to Earth from the surface of the Sun, but most come from outside the solar system. There is a serious problem in identifying the source of cosmic rays. Since light travels in straight lines, we can tell where it comes from simply by looking. Cosmic rays are charged particles, and their direction of motion can be changed by magnetic fields.
Calculations show that low-energy cosmic rays may spiral many times around Earth before entering the atmosphere where we can detect them. If an airplane circles an airport many times before landing, it is difficult for an observer to determine the direction from which it originated. So, too, after a cosmic ray circles Earth several times, it is impossible to know where its journey began.
There are a few clues, however, about where cosmic rays might be generated. Most scientists suspect their origins are related to supernovas star explosions , but the challenge is that for many years cosmic ray origins appeared uniform to observatories examining the entire sky.
A large leap forward in cosmic ray science came in , when the Pierre Auger Observatory which is spread over 3, square kilometers, or 1, square miles, in western Argentina studied the arrival trajectories of 30, cosmic particles. It concluded that there is a difference in how frequently these cosmic rays arrive, depending on where you look.
While their origins are still nebulous, knowing where to look is the first step in learning where they came from, the researchers said. The results were published in Science.
Cosmic rays can even be used for applications outside of astronomy. In November , a research team discovered a possible void in the Great Pyramid of Giza, which was built around B. The researchers found this cavity using muon tomography, which examines cosmic rays and their penetrations through solid objects.
While cosmic rays were only discovered in the s, scientists knew something mysterious was going on as early as the s. That's when French physicist Charles-Augustin de Coulomb — best known for having a unit of electrical charge named after him — observed an electrically charged sphere suddenly and mysteriously not being charged any more.
At the time, air was thought to be an insulator and not an electric conductor. With more work, however, scientists discovered that air can conduct electricity if its molecules are charged or ionized.
This would most commonly happen when the molecules interact with charged particles or X-rays. But where these charged particles came from was a mystery; even attempts to block the charge with large amounts of lead were coming up empty.
On Aug. He discovered three times more ionizing radiation there than on the ground, which meant the radiation had to be coming from outer space. But tracing cosmic ray "origin stories" took more than a century. Among the products of these star explosions are gamma-ray photons, which unlike cosmic rays are not affected by magnetic fields. The gamma-rays studied had the same energy signature as subatomic particles called neutral pions. Pions are produced when protons get stuck in a magnetic field inside the shockwave of the supernova and crash into each other.
In other words, the matching energy signatures showed that protons could move at fast enough speeds within supernovas to create cosmic rays. We know today that galactic cosmic rays are atom fragments such as protons positively charged particles , electrons negatively charged particles and atomic nuclei. While we know now they can be created in supernovas, there may be other sources available for cosmic ray creation.
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