by The Earth is under constant bombardment by cosmic raysshowers of high-energy particles that blast our planet from all directions at close to the speed of light.
While this may sound like the precursor to a sci-fi alien invasion, it is a real phenomenon that scientists have known about for over a century. Despite their dramatic description, cosmic rays are quite normal – they pass through our planet so regularly that a person will have around a million cosmic rays traveling through their body during midnight sleep, according to the University of Birmingham in the UK
Despite their ubiquity, cosmic rays still present scientific mysteries. Although slow-energy cosmic rays that hit World is known to come from the Sunothers of higher energy flow into the Solar system from deep space. The origin of these extrasolar cosmic rays, including suspected sources, is less well known black holes and the supernova explosions that mark the death of massive stars.
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Cosmic rays “have been detected here on Earth for more than 100 years now. But, their origin is still largely unknown,” Julia Tjus, professor of physics and astronomy at Ruhr University in Germany, Space.com said via email. “These tiny particles reach energies that go far beyond what we can reach here on Earth. We are trying to solve measurements that are now more than 100 years old and put the pieces together slowly but steadily.”
What are cosmic rays?
Cosmic rays are streams of high-energy particles The Earth’s Atmosphere at near light speed. They were discovered in the 1900s, and the The term “cosmic rays” was coined by the physicist Robert Millikan in 1925.
Since then, scientists have determined that trillions of cosmic rays hit the Earth every day, but the vast majority are blocked by the planet. magnetosphere and atmosphere.
Over 90% of cosmic rays are hydrogen nuclei (single protons), 9% are helium atomic nuclei, and 1% are nuclei of heavy elements up to iron, according to the University of Chicago. These are called “hadronic particles” because they are made up of hadrons, like protons and neutronwhich is made up of basic particles called quark.
“Yes too electrons and positrons [the antiparticles of electrons] coming to us in cosmic rays but in smaller numbers than the hadronic particles. These are often called cosmic ray electrons,” said Tjus. “Sometimes, people include the high-energy neutral particles – photons and neutrino — in the term cosmic rays, but in most definitions, these are kept separate.”
How do cosmic rays become so energetic?
At the heart of the mystery of cosmic rays is how these particles can achieve incredible energies that cause them to emit close speed of light.
“We know very well the energy of cosmic rays – the universe in a way particles accelerate up to 10²⁰ (1 and 20 zero) electron volts (eV) afterwards,” said Tjus. Large Hadron Collider (LHC) at CERN can only accelerate particles up to 10¹³ eV, many orders of magnitude lower than what the universe can achieve. The mechanism of how particles are accelerated to these extreme energies is not understood.”
One suggestion is that particles could be accelerated to such energies by a shock front created when matter traveling at extremely high velocity collides with a slower medium, causing a sudden change in the latter. This would generate a turbulent magnetic field that could act as a natural and powerful cosmic particle accelerator.
One possible way to generate such conditions is in a supernova, the explosion that occurs when a massive star dies. This explosion would cause the outer layers of the star to disappear at an incredible speed until this amazing material hits the interstellar medium — clouds of gas that move slowly between stars — creating a glowing supernova remnant.
“Supernova remnants are reasonable candidates for cosmic rays coming from within The Milky Way. There is evidence that supernova remnants can accelerate particles up to around GeV energies [around 10⁹ to 10¹² eV],” said Tjus. “At the highest energy, around 10²⁰ eV, we know that these particles must come from other galaxies.”
She said one possible source of these high-energy cosmic rays is active galactic nuclei (AGN), the centers of active galaxies that are powered by feeding. supermassive black holes with masses of millions or billions of times the the mass of the sun.
AGN supermassive black holes are surrounded by material that they gradually eat away at, which is also spun around by their massive gravitational influence, causing them to shine brighter than the combined light of all the surrounding stars. galaxy. Matter in these regions that is not absorbed into the central supermassive black hole can be directed to the poles of the black hole, where it is blasted out as light-speed jets of matter. When these jets hit the surrounding interstellar matter, this collision could also generate cosmic rays.
Another possible source of cosmic rays could be so-called starburst galaxies — meaning those undergoing a very high rate of star formation — that host. gamma ray burstssaid Tjus.
But if cosmic rays come from some of the most violent and visible events in the universe, why do astronomers struggle to trace these charged particles back to these sources?
Cosmic pinball machine
One reason that cosmic ray sources are hard to find is that they are made of charged particles that are affected by magnetic fields. When these particles encounter magnetic fields on their long journey through space to reach us, they are deflected.
So by the time extragalactic cosmic rays reach Earth after traveling millions or billions light year, they have been deflected and redirected many times, ricocheting around the cosmos like a ball in a celestial pinball machine. This makes it almost impossible to reconstruct their original path, but there may be an indirect way of doing it.
“When cosmic rays interact with gas, these interactions result in the production of photons and neutrinos. These are neutral particles that travel directly and can indirectly reveal the origin of cosmic rays,” explained Tjus.
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Cosmic rays are currently studied over a wide range of energies, from 10⁹ eV to 10²⁰ eV, and scientists look at everything from the composition of cosmic rays to their preferred directions in the sky. Through a combination of 3D modeling and precise measurements of neutrinos and photons associated with rays, Tjus believes that progress in understanding where cosmic rays come from and how they are sent with incredible energy can be made. cosmic.
“Cosmic ray measurements can only be solved by putting together different pieces of information from the different messengers observed,” said Tjus. “As of today, there is a wide variety of observatories that provide different pieces of information.”‘
