OMG! A Cosmic Ray!
Have you ever wondered how many ways we have to bring home informations about the universe?
One may think about probes, orbiting satellites, rovers and all the techniques we have learned
to master over time. All the data we collected helped us to put the scattered pieces together:
in fact, when we try to understand our universe, we are actually just trying to solve a giant
puzzle!
But what if I told you that the universe itself is trying to communicate with us, giving us
some tips on how to understand more about it? What if I told you that it is sending
us dms all the time? And, I mean, A LOT OF THEM. Billions of them, every second, reach
the Earth. These messages are called Cosmic Rays.
And when we first demonstrated their existance, we were on a flying balloon. It was 1912.
Since then, they never quit to amaze scientists all over the world.
But what are they? Where do they come from?
Which informations do they carry with them?
Follow me on this journey to know the answer to all these questions, and to fall in love
with Cosmic Rays: I promise you won't be able to resist them.
Let's be clear. Cosmic Rays are not actually Rays: they're
a form of radiations. Although they're called so, they consist of
high-energy emitted particles. These particles are raining down on us from space: they are
little bits of atoms whizzing by us, even through us, all the time.
In this exact moment, you are having a shower of them. Did you bring your shower gel?
They are hitting us, but they aren't causing our bodies any harm, so you don't have to
worry too much about them. But sometimes they can, for example, cause
malfunction to our computers. So you can blame them for making your computer crash.
Particles that are hitting us are actually called “secondary cosmic rays”, because
they are a secondary product of swarms of primary cosmic rays created in the atmosphere,
with interaction that typically produce a cascade of secondary particles starting from
a single energetic particle.
One thing we certainly do know about cosmic rays is that they are comprised of extremely
energetic charged particles like protons, alpha particles, and atomic nuclei like helium
and iron, with miniscule proportions of antiparticles thrown into the mix.
It’s hard to imagine just how shocking the discovery of cosmic rays must have been to
physicists in the early 1900s. The energies of these particles were monumental in comparison
to those of every other particle they had observed until that point. For example, the
average energy of a solar photon is approximately 1.4 electron volts (eV). For reference, a
flying mosquito has an energy of about 1 trillion eV, or 1x1012 eV, but a mosquito is also much,
much larger than a single particle. Meanwhile, an alpha particle emitted during the decay
of Uranium-238 possess 4.27x10⁶ eV of energy. Compare that to a cosmic ray proton, which
has an energy of some 1x10²⁰ eV. That means a proton can only reach that extreme,
macroscopic energy by travelling at almost the speed of light. (try to think about the
famous Einstein's equation!)
Of the nuclei, about 90% are simple protons, 9% are alpha particles and 1% are the nuclei
of heavier elements.A very small fraction are stable particles of antimatter, such
as positrons or antiprotons. The precise nature of this remaining fraction is an area
of active research.
But where do Cosmic Rays come from?
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WE KNOW THAT THEY COME FROM SOMEWHERE IN SPACE.
In 1911 and 1912 Austrian physicist Victor Hess made a series of ascents in a balloon
to take measurements of radiation in the atmosphere. He was looking for the source of an ionizing
radiation that registered on an electroscope – at that day scientists used to think that
the radiation came from the rocks of the Earth.
Victor Hess's balloon flights took such measurements further. In 1911 his balloon reached an altitude
of around 1100 metres, but Hess found "no essential change" in the amount of radiation
compared with ground level. Then, on 7 April 1912, Hess made an ascent to 5300 metres during
a near-total eclipse of the Sun. Since ionization of the atmosphere did not decrease during
the eclipse, he reasoned that the source of the radiation could not be the Sun – it
had to be coming from further out in space. High in the atmosphere, Hess had discovered
a natural source of high-energy particles: cosmic rays.
This was an amazing result:Hess shared the 1936 Nobel prize in physics for his discovery,
and cosmic rays have proved useful in physics experiments – including several at CERN
– since.
But despite being discovered more than a century ago, physicists still don’t know where cosmic
rays exactly come from. This is because particles are actually deflected
by electromagnetic fields. In space, we have some electromagnetic fields
randomly oriented, so that it is very hard to understand where in the universe the cosmic
ray was originated. “The short answer to why we can’t trace
cosmic rays back to their source: magnetic fields,” Julia Tjus, professor at the School
of Physics and Astronomy at Ruhr University in Bochum, Germany, said.
She explains that charged cosmic-ray particles are redirected by the magnetic fields they
pass through on their long journey through space. “As magnetic fields in space have
local, small, randomly oriented structures, a prediction of the exact path of a cosmic-ray
particle is impossible,” she says. This doesn’t mean that we are completely
in the dark about these tiny space bullets, though.
In 2017 scientists found out that they come from EXTRAGALACTIC ZONES:
the researchers found an overabundance of cosmic rays arriving from one specific region
in the sky, located about 120 degrees away from our galactic center, in a direction that
falls outside the Milky Way’s disk and cannot be associated with any possible sources within
the galaxy. The researchers concluded that high-energy cosmic rays must have extragalactic
origins. Fortunately, the more energy a cosmic ray
has, the less it is deflected by a magnetic field, so by studying ultra-high-energy cosmic
rays, researchers should be able to constrain the location of the source even further. And
by ultimately discovering the source of high-energy cosmic rays, astronomers hope to learn both
where exactly they come from, and how they are generated with such great energies.
Nowadays, putting al the pieces together, we know that Cosmic Rays can be divided into
two types: galactic cosmic rays (GCR) and extragalactic
cosmic rays, that are high-energy particles originating outside the solar system, and
solar energetic particles, high-energy particles (predominantly protons) emitted by the sun,
primarily in solar eruptions.
But how can we detect and study Cosmic Rays?
While the detection of cosmic rays has been associated with balloon flights ever since,
the upper atmosphere isn’t the most convenient laboratory to investigate the high-energy
particle collisions they produce.
To study the collisions caused by cosmic rays, particle physicists retreated below ground,
employing increasingly monstrous particle accelerators to slam together particles in
an attempt to replicate the collisions that cosmic rays spark in the upper atmosphere.
This quest has culminated with CERN’s Large Hadron Collider (LHC) with a 16-mile (26
km) circumference deep beneath the French/Swiss border. Yet, despite its impressive size,
power and utility, the LHC still can’t reach the energies produced by cosmic ray collisions.
Another huge effort was made in order to build the famous ICE CUBE NEUTRINO DETECTOR, a neutrino
detector built at a scientific installation under the Antarctic Ice in the South Pole.
Spherical geometry detectors are arranged in vertical wells of sixty modules each. The
wells are built using a cone-shaped "drill" that sprays hot water.
On wikipedia we can read: “The aim of the IceCube Neutrino project
is the detection of high energy neutrinos. Most of these neutrinos are generated by the
interaction of cosmic rays with the nuclei of the Earth 's atmosphere , but an unknown
fraction of these could have astronomical origins . To distinguish the two sources, statistical analyzes on
the direction and angle of entry of neutrinos into ice are taken into consideration . Very
roughly it can be said that a neutrino coming from above is more likelyto have been produced
by the penetration of the shower of cosmic rays into the atmosphere; while, those neutrinos
that come from below (from the bottom of the sea) are more likely to have a different
origin.”
It happens sometimes that scientists find something unexpected. Maybe they dont even
know what to say in front of their new amazing discovery, so they give weird names to it.
This was the case of the so-called Oh-My-God PARTICLE.
OMG Particle was an high energy cosmic ray detected on 15 october, 1991 by University
of Utah. Her name derives from the stupor that it caused
in the astrophysics community, because its energy was estimated to be around 3*10^20
eV, the most energetic particle ever detected ever since that day.
Using a cryterium from comparison, it was like a baseball ball reaching a velocity of
94 km/h. That means it was travelling at the 99.9999999999951%
of the speed of light. Due to relativistic time dilation, at that
speed, the OMG particle could travel to our nearest neighbor star, Proxima Centauri, in
0.43 milliseconds of the particle's own time. It could continue on to our galactic core
by the time you've finished reading this sentence (from its own perspective).
"OMG" was the nickname given to the first example of what are now known as ultra-high-energy
cosmic rays.
Since the Oh-My-God particle was detected, at least other 72 of similar particles, i.e.
with an energy of more than 5,7×1019 eV, were detected, confirming the existance of
a still-unknown generator of accelerating particles. Considering that the energy of
the vast majority of the particles goes from 10 MeV and 10 GeV, the detection of these
type of particle is a very rare event.
At this point, we are finally ready to answer the last question: what type of messages do
Cosmic Rays carry with them?
What makes cosmic rays useful as messengers is that they carry the traces of their origins.
By studying the frequency with which different particle occur, we are able to determine the
relative abundance of elements within the universe.
But another field of research in which we find cosmic rays useful as messengers is the
one studying antimatter. Once we have detected a cosmic particle, we
are able to determine its velocity, its trajectory, its radiation, its mass and its energy, as
well as wether the particle is matter or antimatter. For this purpose, scientists installed a useful
instrument on the International space station, that is called Alpha Magnetic Spectrometer,
which is able to measure 50 million of particles per day, with information about each particle
being sent in real time from the space station to laboratories on Earth.
This data contain useful informations about antimatter, that will enable us to understand
more about it. So, if you happen to look at the sky in the
night, you may see the ISS, where the Alpha Magnetic Spectrometer receives the tiny cute
messengers that carry cosmic secrets.
"This video ends here! Thanks for watching everyone! What did you know about Cosmic Rays?
Did you find these informations useful? Were you amazed by the huge energy owned by the
OMG particle? Is there anything more you want to hear about life on other planets? Let me
know in the comments below, be sure to subscribe, and I'll see you next time on the channel!"
Credits: Astronomy, TED-Ed, Wikipedia, Space.com, Nasa, Esa