The Gamma-ray speed

Fireworks in the sky

This is Leyre. One of the things he likes the most is driving. It does not have problems in taking the car and to do kilometers and kilometers seeing the landscape happen. Who is really moving, she or the landscape? Questions like this gave rise to the theory of relativity, a new way of thinking about space and time. Leyre uses the MAGIC telescopes to precisely test this theory.

Here we are all Gamma Ray Hunters, but some of us are more selective than others.

Of all the gamma rays, the ones that interest me are those that come from flares.

What are flares? We use the flare concept to refer to a period in which we get more gamma rays than usual from a particular position in the Universe.

Our way of understanding a flare is not so different from its real meaning: it could be compared to lighting a match that is quickly consumed. Although, of course, it is a flame that is millions of light years away and with a much higher energy.

For example, in June 2015 a flare was detected from blazar 3C279, five billion light years. The last time activity was detected in it was in 1991! After 14 years appears without warning … And, so far, it is the most luminous high energy object that has been observed.

In this video each circle represents a gamma ray detected by FERMI. The size and color of the circles give an idea of its magnitude. Notice how at a certain moment, the amount of gamma rays increases: that is the flare.

Normally 3C279 is one of the many active galaxies that we can observe.

But from one day to the next it became the brightest object in the sky Gamma. And so for 4 days. That was precisely the flare.

The flare started on June 14, 2015 and 4 days later it was over. We still do not know why it happened.

Each day of observation we make a plan of the objects that we want to observe. For today we have remnants of supernovas, binary systems, pulsars, clusters of galaxies, …

The flares, which are the ones that interest me, are never on the menu of the day. But of course, you never know when they will happen.

In April 2011, the FERMI satellite detected a flare in the Crab nebula. In the image you can see how the intensity of the emission changes before and after the event. These flashes are fast and you have to be alert to catch them.

Image Credit: NASA/DOE/Fermi LAT/R. Buehler

Dictionary of the gamma ray hunter

Active Galactic Nuclei

The party is inside

This type of galaxies (known as AGN) have a compact central core that generates much more radiation than usual. It is believed that this emission is due to the accretion of matter in a supermassive black hole located at its center. They are the most luminous persistent sources known in the Universe.

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Black Hole

We love everything unknown and the secrets that a black hole keeps are many

It is a supermassive astronomical object that shows huge gravitational effects so that nothing (neither particles nor electromagnetic radiation) can overcome its event horizon. That is, nothing can escape from within.


No, it is not a 'blazer', we are no shopping

It is a particular type of active galactic nucleus, with the characteristic that its jet points directly at the Earth. In one sentence, it is a very compact energy source associated with a black hole in the center of a galaxy that is pointing us.

Cherenkov Radiation

This phenomenon with a name that looks like a James Bond enemy is our maximum object of study

Electromagnetic radiation emitted when a charged particle passes through a dielectric medium at a speed greater than the phase velocity of light in that medium. When a very energetic gamma photon or cosmic ray interacts with the Earth’s atmosphere, they produce a cascade of particles travelling at high speed. The Cherenkov radiation of these charged particles is used to determine the origin and intensity of cosmic rays or gammas.

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Cherenkov Telescopes

Our favorite toys

They are high energy gamma photon detectors located on the Earth’s surface. They have a mirror to collect the light and focus it towards the camera. They detect light produced by the Cherenkov effect from the blue to the ultraviolet of the electromagnetic spectrum. The images taken by the camera allow us to identify if the incident particle in the atmosphere is a gamma ray and at the same time determine the direction and its energy. The MAGIC telescopes at Roque de los Muchachos (La Palma) are an example.

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Cosmic Rays

One must know how to choose between rays, particles and sparks!

Cosmic rays are high energy radiation composed mainly of very energetic protons and atomic nuclei. They travel almost at the speed of light and when they hit the Earth’s atmosphere they produce cascades of particles: these particles generate Cherenkov radiation and some can even reach the surface of the Earth. But when the cosmic rays reach the Earth, it is impossible to know their origin since their trajectory has changed because they have travelled through magnetic fields that changed their initial direction.

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Dark Matter

And what will it be?

How to define something that is not known? We know of its existence because we detect it indirectly thanks to the gravitational effects it causes in visible matter, but we can not study it directly. This is because it does not interact with the electromagnetic force so we do not know what it is composed of. And we are talking about something that represents 25% of everything known! So it’s better not to despise it and try to unravel what is …

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Duality Particle Wave

But what is it?

It is a quantum phenomenon by which in certain occasions the particles acquire characteristic of a wave. And the other way round. What we would expect to always behave like a wave (for example light) sometimes does it as a particle. This concept was introduced by Louis-Victor de Broglie and has been experimentally demonstrated.

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These really are the events of the year

When we talk about events in this field, we refer to each of the detections we make in telescopes. For each of them we have certain information such as the position in the sky, the intensity, etc. That allows us to classify them. We are interested in having many events so that we can do statistics a posteriori and draw conclusions.

Gamma Ray

Yes we can!

Extreme frequency electromagnetic ionizing radiation (above 10 exahertz). It is the most energetic range of the electromagnetic spectrum. The direction with which they arrive at the Earth indicates the direction from where they originated.

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Lorentz Covariance

The privileges of certain equations ...

Certain physical equations have this characteristic by which they do not change shape when certain changes of coordinates are given. The Special Theory of Relativity requires that the Laws of Physics must take the same form in any inertial reference system. That is, if we have two observers whose coordinates can be related by a Lorentz transformation, any equation with covariant magnitudes will be written equal for both.

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Below you will learn what a quasar is ... well the same in little one!

It is a binary star system that produces high-energy electromagnetic radiation. Its characteristics are similar to those of quasars, but on a smaller scale. Microquasars produce strong and variable radio emissions often in the form of jet and have an accretion disk surrounding a compact object (black hole or neutron star) that is very bright in the range of X-rays.

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What shape do the clouds have?

Nebulae are regions of the interstellar medium composed basically of gases and some chemical elements in the form of cosmic dust. In them are born many of the stars by condensation and aggregation of matter. Sometimes it’s just the remains of extinct stars.

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Particle Shower

Niagara Falls of particles!

Rain of particles resulting from the interaction between high energy particles with a dense medium, for example, the Earth’s atmosphere. Each of these secondary particles produced in turn creates a cascade of its own, so that they end up producing a large number of low-energy particles.


Now you see me, now you do not see me

The word ‘pulsar’ comes from the shortening of pulsating star and it is precisely this: a star from which we get a signal in a discontinuous way. Stated more formally, it is a neutron star that emits electromagnetic radiation while it is spinning. The emissions are due to the strong magnetic field they have and the pulse is related to the rotation period of the object and the orientation relative to the Earth. One of the best known and studied is the pulsar of the Crab Nebula, very beautiful, by the way.

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Quantum Gravity

This sounds getting worse ...

This field of physics aims to unite the quantum field theory, which applies the principles of quantum mechanics to classical systems of continuous fields, with general relativity. We want to define a unified mathematical basis with which all the forces of nature can be described, the Unified Field Theory.

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'Quasi' we confuse them with stars

They are the farthest and most energetic members of a class of objects called active core galaxies. Its name comes from ‘quasi-stellar’, almost stars, since, when they were discovered, using optical instruments, it was very difficult to distinguish them from the stars. However, its emission spectrum was clearly unique. They have usually been formed by the collision of galaxies whose central black holes have merged to form a supermassive black hole or a binary system of black holes.

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Supernova Remnant

A large cloud of candies in the cosmos

When a star explodes (supernova) a nebula structure is created around it formed by the material ejected from the explosion along with interstellar material.

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Theory of relativity

In this life, everything is relative, ... or not!

Albert Einstein was the genius who decided to turn Newtonian mechanics to make it compatible with electromagnetism with his Theories of Special and General Relativity. The first is applicable to the movement of bodies in the absence of gravitational forces and in the second, Newtonian gravity is replaced with more complex formulas, although for weak fields and small velocities it coincides numerically with classical theory.

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