Cosmic ray

Tiny bits fly through space.

They come from far away. They move very fast. These bits come from the Sun and far stars.

They hit the air around Earth. This makes a big splash. This splash makes many new bits.

These new bits can reach the ground.

Some bits pass through you. One bit passes through your head every second.

They are all around us. They are part of our world.

Cosmic rays are tiny bits of matter that fly through space.

They move at nearly the speed of light. Most come from outside our solar system. They can come from the Sun or far stars. Some may even come from exploding stars called supernovae.

In 1912, a scientist named Victor Hess found them. He flew high in a balloon. He saw that radiation grew stronger as he went up. This proved the rays came from space.

Hess won a Nobel Prize for this work.

When these rays hit our air, they cause a big splash. They hit atoms in the atmosphere. This makes a shower of new particles. Some of these are called muons.

Muons can travel through the air and even go underground. About one muon passes through a space the size of a human head every second. Most cosmic rays are protons. A proton is a tiny part of an atom. About 99% of these rays are nuclei from atoms. These nuclei are the centers of atoms without their outer shells.

Cosmic rays are tiny bits of matter that fly through space.

These particles move at nearly the speed of light. They come from many different places in the universe. Some come from our own Sun. Most come from far away in the Milky Way or distant galaxies.

Some might even come from the explosions of dying stars called supernovae. These rays are very important to study because they have huge amounts of energy. This energy can even damage small electronics or living things outside of Earth's protection.

When a cosmic ray hits our atmosphere, a big chain reaction starts.

The ray hits atoms in the air and bursts them into many smaller bits. This creates a shower of new particles called secondary particles. Some of these are called pions. These pions quickly turn into other particles called muons.

Muons are special because they do not interact strongly with matter. This allows them to travel through the air and even go below the ground. About one muon passes through a space the size of a human head every second.

Scientists did not always know these rays came from space. In 1912, a scientist named Victor Hess went on a big adventure.

He flew a free balloon high into the sky to 5,300 metres. He used special tools called electrometers to measure radiation. He found that radiation actually grew stronger as he went higher. This proved the rays were entering our atmosphere from above. Hess later won the Nobel Prize in Physics in 1936 for this discovery.

We know a lot about what these rays are made of now.

About 99% of the primary rays are nuclei from common atoms. Most of these are simple protons, which are the centers of hydrogen atoms. About 9% are alpha particles, which are the centers of helium atoms. The rest are mostly heavier elements or single electrons. Scientists also look for antimatter, which is a very small part of the rays. They use satellites and space probes to measure these particles directly.

Learning about cosmic rays helps us understand the whole universe.

These rays act like messengers from deep space. They show us how powerful stars and galaxies can be. For example, some rays have as much energy as a flying baseball. This is a huge amount of energy for one tiny particle. By studying them, we learn how things like active galactic nuclei work. We can see how the most extreme parts of space behave.

Cosmic rays, also called astroparticles, are high-energy particles or clusters of particles that travel through space at nearly the speed of light.

These particles originate from various locations, including our Sun, the Milky Way, and even distant galaxies. They are important to study because they carry immense energy. This energy can damage microelectronics and living things that lack protection from an atmosphere or magnetic field.

While many are deflected by the magnetosphere or the heliosphere, some reach Earth.

When a primary cosmic ray hits Earth's atmosphere, it triggers a complex chain reaction.

The ray strikes atoms in the air, causing them to burst into many smaller bits of matter. This process creates a cascade of secondary particles, such as pions and neutrinos. The charged pions produced in this collision quickly decay, which results in the creation of muons.

Unlike pions, muons do not interact strongly with matter. This characteristic allows them to travel through the atmosphere and even penetrate below ground level. In fact, about one muon passes through a volume the size of a human head every second.

Primary cosmic rays have a specific chemical makeup. About 99% are bare nuclei, which are the centers of atoms stripped of their electrons. Within this group, approximately 90% are simple protons, also known as hydrogen nuclei. About 9% are alpha particles, which are identical to helium nuclei. The remaining 1% consists of the nuclei of heavier elements, known as HZE ions.

A very small fraction of rays are solitary electrons, which are a type of beta particle. There is also a tiny, rare fraction of stable antimatter, such as antiprotons or positrons.

For a long time, scientists believed radiation came only from the ground. In 1909, Theodor Wulf used an electrometer to show higher radiation at the top of the Eiffel Tower. However, the true origin of these rays remained a mystery until 1912.

Victor Hess conducted a famous experiment by flying a free balloon to an altitude of 5,300 metres. He used enhanced Wulf electrometers to measure ionization rates. Hess discovered that radiation levels actually increased with altitude.

To ensure the radiation did not come from the Sun, he performed an ascent during a near-total eclipse. His findings proved that high-penetrating radiation enters our atmosphere from above. Hess was awarded the Nobel Prize in Physics in 1936 for this discovery.

As research progressed, scientists refined their understanding of these particles. In the 1920s, Robert Millikan coined the term "cosmic ray." He initially believed they were gamma rays, which are high-energy photons. However, Jacob Clay found in 1927 that cosmic ray intensity changes based on location. This indicated that the rays are charged particles deflected by Earth's magnetic field.

Later, researchers like Pierre Auger and Bruno Rossi helped explain how these particles create massive showers of secondary radiation. These discoveries transformed our view of the high-energy universe.

The energy levels of cosmic rays are truly staggering. Most cosmic rays have energies that peak at a specific distribution, but some are much stronger. Ultra-high-energy cosmic rays can reach energies comparable to the kinetic energy of a baseball.

This is significantly higher than the energy produced by the Large Hadron Collider. Such extreme energy might be achieved through the centrifugal mechanism of acceleration in active galactic nuclei. Studying these particles allows us to observe the most powerful processes in space.

Today, cosmic rays serve as vital tools for modern astronomy. Data from the Fermi Space Telescope suggests that many primary cosmic rays come from supernova explosions.

Observations of neutrinos and gamma rays from the blazar TXS 0506+056 also suggest that active galactic nuclei produce them. By using satellites and particle detectors, scientists continue to trace these particles back to their distant sources. This work connects the tiny scale of subatomic particles to the massive scale of entire galaxies.