The world is under constant bombardment cosmic raysShowers of high-energy particles blasting our planet from all directions at near the speed of light.
While this may seem like a foreshadowing of a science fiction alien invasion, it is a real phenomenon that scientists have been aware of for over a century. Despite their dramatic description, cosmic rays are actually pretty ordinary; They pass through our planet so regularly that during an average night’s sleep, a person will have approximately one million cosmic rays traveling through their body. University of Birmingham in england
Despite their ubiquity, cosmic rays still present scientific mysteries. As slow energy cosmic rays hit Soil It is known to originate from sunOthers with higher energy solar system deeply space. The origins of these extrasolar cosmic rays are less known, and questionable sources include: black holes And supernova Explosions that signal the death of massive stars.
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“Cosmic rays have been detected on Earth for over 100 years. However, their origins are largely unknown,” said Julia Tjus, professor of physics and science. astronomy The information was provided to Space.com via email from the Ruhr University in Germany. “These tiny particles reach energies far beyond what we can reach on Earth. We are trying to solve a puzzle that is more than 100 years old and slowly but steadily put the pieces together.”
What are cosmic rays?
Cosmic rays are streams of colliding high-energy particles. earth atmosphere at a speed close to the speed of light. They were discovered in the 1900s and The term “cosmic rays” was coined by physicist Robert Millikan in 1925..
Since then, scientists have determined that trillions of cosmic rays hit the Earth every day, but the vast majority of them are blocked by the planet’s rays. magnetosphere and atmosphere.
According to the University of Chicago, more than 90% of cosmic rays are hydrogen nuclei (single protons), 9% are atomic nuclei of helium, and 1% are nuclei of elements as heavy as iron. Because these consist of hadrons, they are called “hadronic particles”. protons And neutronsIt consists of fundamental particles called particles. quarks.
“Also there electrons and positrons [the antiparticles of electrons] It comes to us in the form of cosmic rays, but in smaller numbers than hadronic particles. These are often called cosmic ray electrons,” Tjus said. “Sometimes people also include neutral high-energy particles – photons and neutrinos – with the term cosmic rays, but in most definitions they are kept separate.”
How can cosmic rays be so energetic?
The heart of the cosmic ray mystery is how these particles can reach incredible energies, causing them to accelerate close to each other. speed of light.
“We know the energies of cosmic rays pretty well – Universe Tjus said he somehow accelerated the particles up to 10²⁰ (1 followed by 20 zeros) electronvolts (eV). “In comparison, Earth-bound accelerators, Large Hadron Collider (LHC) at CERN can only accelerate particles to 10¹³ eV; This is much lower in magnitude than the universe can achieve. “The mechanism of how particles are accelerated to these extreme energies is not understood.”
One suggestion is that particles can be accelerated to such energies by a shock front formed when a material moving at an incredibly high speed crashes into a slower-moving medium, creating a sudden change in the latter. This would create a turbulent magnetic field that could act as a natural and powerful cosmic particle accelerator.
One possible way to create such conditions would be a supernova, the explosion that occurs when a massive star dies. This explosion will eject the star’s outer layers at incredible speeds until this stellar material eventually crashes into the star. interstellar medium – clouds of gas moving slowly between them stars — creating a glowing supernova remnant.
“Supernova remnants are plausible candidates for cosmic rays coming from within the universe.” Milky Way. There is evidence that supernova remnants can accelerate particles to energies of about GeV [around 10⁹ to 10¹² eV]“We know that at the highest energies around 10²⁰ eV, these particles must have come from other galaxies,” Tjus said.
One plausible source of these high-energy cosmic rays, he said, is active galactic nuclei (AGN), which are the centers of active galaxies supported by nutrition. supermassive black holes have masses that are millions or billions of times mass of the sun.
AGN supermassive black holes are gradually surrounded by the material they feed on; They also churn around with their tremendous gravitational effects, causing them to shine brighter than the combined light of every star around them. galaxy. Matter in these regions that is not fed into the central supermassive black hole can be channeled to the poles of the black hole, where it is ejected as jets of matter at near the speed of light. When these jets hit surrounding interstellar material, the collision can also produce cosmic rays.
Another possible source of cosmic rays could be so-called starburst galaxies, that is, galaxies that are undergoing extraordinarily high rates of star formation. gamma ray burstssaid Tjus.
So if cosmic rays come from some of the most violent and remarkable events in the universe, why do astronomers have trouble tracking these charged particles to these sources?
A cosmic pinball machine
One reason it is difficult to find sources of cosmic rays is that they consist of charged particles that are affected by magnetic fields. These particles change direction when they encounter magnetic fields on their long journey to reach us in space.
That is, until extragalactic cosmic rays reach Earth after traveling millions or billions of ways. light years, they have been deflected and redirected many times, bouncing around the cosmos like a ball in a celestial pinball machine. This makes reconstruction of their original path almost impossible, but there may be an indirect way to do this.
“When cosmic rays interact with gas, these interactions lead to the production of photons and neutrinos. These are straight-moving neutral particles and can therefore indirectly reveal the origin of cosmic rays,” Tjus explained.
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Cosmic rays are currently studied across a wide range of energies, from 10⁹ eV to 10²⁰ eV, and scientists are studying everything from the composition of cosmic rays to their preferred direction in the sky. Tjus thinks that with a combination of 3D modeling and precise measurements of the neutrinos and photons associated with cosmic rays, progress can be made in understanding where cosmic rays come from and how they are launched with such incredible energies.
“The cosmic rays riddle can only be solved by combining different information from different observed precursors,” Tjus said. “As of today, there are a wide variety of observatories providing different information.”‘