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COSMIC ENERGY
Ancient Abdera. Here in the middle of the 5th century BC was born Democritus,
the philosopher who believed that everything around us
is made up of small particles invisible to the eye.
These particles were so simple that they could not be destroyed.
Atoms. In this place, within the walls of the city, of which now there are only long forgotten ruins,
originates the modern atomic physics.
Astronomy is mostly observational science.
Until the invention of the telescope in the early 17th century,
people had one single "tool" for obtaining information from the surrounding universe - the human eye.
It was only a few decades ago, when we started to use for astronomical observations
radio waves, microwaves, infrared, ultraviolet, X-rays and gamma rays-
virtually the entire electromagnetic spectrum.
But not always it's about chasing photons.
There are also other particles that come to us from the depths of the universe
with enormous energy and speed close to the speed of light.
When they reach our planet, these particles ionize part of the Earth's atmosphere.
Initially it was thought that these are gamma rays, i.e. photons with tremendous energy.
However, later was found that their nature isn't electromagnetic and these are mainly charged particles,
being affected by magnetic field of the Earth.
Although erroneously called "cosmic rays" nearly one hundred years ago,
this name is still used today.
In 1912, Austrian physicist Victor Hess conducted a series of experiments,
including hazardous balloon flights at altitudes above 5000 meters.
By exploring the level of ionization of the air at different altitudes,
he concluded that the ionization is caused by radiation
that enters the atmosphere from outer space.
This discovery earned him the Nobel Prize for Physics in 1936.
If we use contemporary detector for high-energy particles elevating a balloon high in the stratosphere,
we could find that an increase of the altitude leads to enhancing the level of cosmic radiation.
At an altitude of about 15,000 meters above sea level, the number of detected particles reaches its maximum.
Higher up the radiation rapidly declines.
Such an experiment proves that the particles that bombard the Earth
have a secondary origin and are formed in the Earth's atmosphere.
These cosmic particles most often have a positive electrical charge.
These are mainly protons - nuclei of hydrogen atoms.
In addition there are also some helium nuclei called alpha particles.
Protons and alpha particles are in a ratio, corresponding to the two most common elements in the universe:
90 percent hydrogen and 9 percent helium.
Small amounts of electrons and nuclei of heavier chemical elements also have been found.
Cosmic rays have different sources, but the origin of some of them still remains a mystery to science.
Particles with relatively low energy are formed as a result of solar activity-
solar flares and coronal mass ejection into interplanetary space.
Streams of charged particles from the Sun often reach the planet,
but Earth's magnetic field acts as a kind of shield that protects us from such a devastating impact.
Higher energy particles are far more distant travelers. They usually come from the depths of the Milky Way.
Supernovae, pulsars and black holes are considered the most likely candidates for the source of cosmic rays.
Since the route of charged particles follows the magnetic fields of our galaxy,
they come to us from all directions, and their source is difficult to be identified with certainty.
Magnetosphere and solar wind repel large part of them, but some still manage to get to our planet.
However there are extremely high energy particles, millions and even billions of times more powerful
than those created in the Large Hadron Collider.
Such processes can only take place outside the Milky Way, in distant active galactic nuclei,
wherein supermassive black holes with a mass of a million times our Sun cause radiation of colossal amounts of energy.
What happens when a high speed charged particle, such as proton reaches the Earth and enters its atmosphere?
High in the stratosphere the proton hits a nucleus of nitrogen or oxygen atom.
Similar collisions of high-energy protons occur in man-made accelerators
and lead to the emergence of new particles - pions.
The pion is extremely unstable particle.
It exists only billionths of a second, after which it decays to other particles, mostly muon and a neutrino.
Muons are also unstable, their mean lifetime is about two microseconds.
In such a short time even light fails to pass more than 600 meters!
However, some muons still manage to reach the Earth's surface travelling few dozen kilometers through it.
How they manage to do it?
The reason is they travel at very near the speed of light.
According to modern physics, when an object is moving so fast,
the time starts flowing in a different way, it is the so called time-dilation.
Life of muons is extended repeatedly and they can even be registered by terrestrial detectors.
The path of the muons does not end at the Earth's surface.
They have an electric charge equal to that of electrons but are 200 times heavier than them.
Because of the high speed their energy is enormous and large part of them penetrate deeply into the Earth,
passing through dozens or even hundreds of meters of rock and soil.
Some of them even managed to reach 4,000 meters below ground before their energy being completely absorbed.
By the early 30s of the twentieth century there were known only the electron, the proton and the neutron,
the fundamental particles of which all atoms are built.
At that time Hideki Yukawa published a theory that predicted the existence of mesons,
charged particles heavier than electrons, but lighter than protons.
Before the accelerators were built, the only source of high-energy particles remain cosmic rays.
Studying them resulted to discovery of some new sub-atomic particles: positively charged electron, called positron,
muon, and a little later the real mesons: pion and kaon.
For many years, the efforts of researchers have been focused on unification and classification
of all detected particles and interactions, creating a refined theory called the Standard Model.
When the primary rays coming from the depths of space hit the atoms of the Earth's atmosphere,
chain reactions take place to form a large number of secondary particles.
Their number is ever increasing, forming so called particle showers.
A research and educational project started in 2009, which deployed hundreds of detectors connected in a global network
for measuring and recording these secondary cosmic rays reaching any place on our planet.
The project is called ERGO and it continuously acquires and stores real time information
from all the detectors scattered around the world.
Experimental data can help to solve one of the current problems of our time - climate change on our planet.
It turns out that cosmic rays could affect the formation of cloud cover on Earth
which in turn is directly related to temperature changes.
This relationship was discovered by Henrik Svensmark, a professor at the Danish National Space Institute.
But how the energy born in remote parts of our galaxy, and even in the depths of other distant galaxies
could be able to form the climate of our planet?
The answer is hidden in the complex interaction between solar activity and high-energy flux in our galaxy.
When you turn the radio on, music and voices of sound frequency could be heard.
But this is not the frequency of radio waves, caught by our receiver.
Radio engineers call this process modulation-
audible low frequency oscillations modulate the high frequency electromagnetic waves,
which allows information to be transmitted over long distances.
Something very much like that happens with cosmic rays and solar wind.
Although we're not talking of electromagnetic waves here, the process is similar.
In periods of high solar activity, as a result of solar flares,
huge clouds of charged particles leave the surface of the Sun and travel in the interplanetary space.
This phenomenon is called solar wind.
Since these particles are charged, they form a strong electromagnetic field around them.
Reaching the Earth, the solar wind can affect the higher energy rays coming from the galaxy,
shielding and repelling some of them.
Detectors on the ground may report decreases in the cosmic radiation.
This phenomenon is known as Forbush decrease and it is in fact a process of modulation
where the high energetic cosmic rays could be affected by lower energy flows coming from our Sun.
Cosmic rays ionize the atmosphere and create ion nuclei around which a condensation of water could be triggered.
This may initiate a cloud formation.
Such mechanism explains how the higher solar activity can lead to a decrease in cosmic radiation,
which in turn prevents the formation of cloud cover on the Earth.
Therefore, the activity of the Sun could indirectly affect what we call global warming.
But still our planet is a quiet and secure place to live.
The atmosphere and the Earth's magnetic field
provide reliable protection against primary, high power cosmic rays.
Radiation in space, however, can be deadly and it may turn into a real disaster
for the crew of future interplanetary or even interstellar missions.
This will probably be one of the greatest challenges on our endeavour to the stars.
narrator Zdravko Beshendjiev
script Zlatan Merakov
camera Dimitar Takov
music Brian Eno Lauge & Baba Gnohm Stephan Elgner
animation Nebeto NASA
in cooperation with ERGO Energetic Ray Global Observatory
production Nebeto 2012