Night 2:The Microquasar Wakes Up
How many MAGICs fit in the sky?
How many MAGICs fit in the sky?
The sky is huge and our telescope field of view is very small. But what exactly does “very small” mean? Would you be able to work how many MAGICs would be needed to cover the sky?
We can only see a part of the sky with the MAGIC telescopes. How much? A good way to get an idea is to compare it with the size of the full moon.
Look in the notebook on the right to see how the fraction of the sky that MAGIC sees is calculated. Sure, you know the trigonometry to use but when it comes to calculating things from telescopes, it’s more fun this way, right ?!
With such a small window and such a large sky, how would we know that something is happening? Luckily, other telescopes help us. If we were alone in trying to catch gamma rays, it would almost be like looking for a needle in a haystack.
We have catalogues of the exact positions of the sources of gamma rays detected by satellites such as Fermi, and there we aim to analyse them in detail.
The coordinates of Cygnus-X1 (I know them off by heart RA = 19: 58: 21, DEC = 35: 12: 5) place it right in the middle of the tail of the Swan. It’s not exactly “my” microquasar, but I have been after it for so long, waiting for the moment when it gives us a signal, that it sends us gamma rays that we can hunt … that it’s almost become my obsession.
Cygnus-X1 in the constellation of the Swan. Right there is the microquasar. Image Credit: Dan Lessmann
It doesn’t make sense to point the MAGIC telescopes to Cygnus-X1 all the time. I have to wait for the black hole to swallow so much matter that it starts to “shoot” high-energy gamma rays. The rest of the hunters want to see other sources, and you know how it goes, we all help each other.
But, seriously … Cygnus-X1 you need to wake up now!
:( Anyway, in the meantime, I just keep on working. It’s not so bad because … we get to travel a lot!
In fact, I have to leave you to it so that I can finish packing: I’m going to the United States for three months to work with Meredith and Marvin (do you remember them? They’re the ones who work at HAWC and Fermi). See you when I get there!
Image Credit: Tumblr
Alba’s scientific notebook
This is my scientific notebook. Here, I jot down everything I do … it’s important to write down everything, at least for me because, if not, then I don’t remember everything I’ve done.
Now it’s time to calculate HOW MANY MAGIC TELESCOPES YOU NEED TO SEE THE WHOLE SKY
As always, to start with this iPython we have to load the libraries that we’ll use. It’s one of the best things about Python: there are a lot of people creating very useful libraries.
import math
The first thing I need to do to calculate how many MAGICs I need to cover the sky, is to work out how big the sky is. Yes! The universe is infinite, but when I look at a star, I can also see everything behind and in front of it. Therefore, I want to know the size of the sky in directions, not in m, km, parsecs, light years or anything like that … and the directions are calculated in steradians, which are defined as the explored surface divided by the square of the distance where the surface is.
It seems complicated, but let’s go through it together … it might not be so bad afater all. For a sphere with a radius of 10 Km that we’re in the middle of:
radio=10000
superficie = 4 * math.pi * (radio*radio)
print ("The surface of the sphere with radius of ",radio, " metres is ", superficie, "square metres")
The surface of the sphere with radius 10000 metres is 1256637061.44 square metres
Now we just need to divide the surface by the radius squared and we will have the steradians for a sphere of 10 km that we’re in the middle of.
stereorradianes = superficie / (radio*radio)
print ("The angular dimension of a sphere of 10 km that we're in the middle of is ", stereorradianes, "steradians")
The angular dimension of a sphere of 10 km that we're in the middle of is 12.5663706144 steradians
In fact, if you have noticed, this is independent of the size of the sphere. Therefore, the angular size of the sky that we see from the Earth is the same. Yup, that’s right. The Earth is at the centre of the universe visible from Earth. But that doesn’t mean that it’s at the centre of the universe!
Now, I need to calculate the size of the section of sky that can be seen by MAGIC. I know that, in degrees, the size is 2 degrees by 2 degrees, that is 4 square degrees. But I have to turn it into steradians.
Luckily, during the time that I passed at high school, I was thaught that in trigonometry 180 degrees are Pi radians.
GradoARadian = math.pi / 180.0
GradoCuadradoAStereorradian = GradoARadian * GradoARadian
AreaDeMAGIC = 4 * GradoCuadradoAStereorradian
print ("The area covered by MAGIC are", AreaDeMAGIC, "steradians.")
The area covered by MAGIC is 0.00121846967915 steradians.
I just need to divide them
** Angular size of the sky / Angular size of MAGIC **
print ("To cover the full sky we need ", stereorradians / AreaDeMAGIC, "MAGICs")
To cover the full sky we need 10313.2403124 MAGICs
But how small does that make MAGIC? Or rather, how big does that make the sky?
Dictionary of the gamma ray hunter
Active Galactic Nuclei
There's party going on inside!
This type of galaxy (known as AGN) has 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 in the centre. They are the most luminous persistent sources known in the Universe.
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Black Hole
We love everything unknown. And a black hole keeps many secrets.
A black hole 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.
Blazar
No, it's not a 'blazer', we aren't going shopping
A blazar is a particular type of active galactic nucleus, characterised by the fact that its jet points directly towards the Earth. In other words, it’s a very compact energy source associated with a black hole in the centre of a galaxy that’s pointing at us.
Cherenkov Radiation
It may sound like the name of a ames Bond villain, but this phenomenon is actually our maximum object of study
Cherenkov radiation is the 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, a high-speed cascade of particles is produced. The Cherenkov radiation of these charged particles is used to determine the origin and intensity of cosmic or gamma rays.
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Cherenkov Telescopes
Our favourite toys!
Cherenkov telescopes are high-energy gamma photon detectors located on the Earth’s surface. They have a mirror to gather light and focus it towards the camera. They detect light produced by the Cherenkov effect from blue to ultraviolet on the electromagnetic spectrum. The images taken by the camera allow us to identify if the particular particle in the atmosphere is a gamma ray and at the same time determine its direction and energy. The MAGIC telescopes at Roque de Los Muchachos (La Palma) are an example.
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Cosmic Rays
You need to know how to distinguish between rays, particles and sparks!
Cosmic rays are examples of high-energy radiation composed mainly of highly 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. However, when cosmic rays reach the Earth, it is impossible to know their origin, because their trajectory has changed. This is due to the fact that they have travelled through magnetic fields which force them to change their initial direction.
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Dark Matter
What can it be?
How can we define something that is unknown? We know of its existence because we detect it indirectly thanks to the gravitational effects it causes in visible matter, but we can’t study it directly. This is because it doesn’t interact with the electromagnetic force so we don’t know what it is composed of. Here, we are talking about something that represents 25% of everything known! So, it’s better not to discount it, but rather try to shed light on what it is …
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Duality Particle Wave
But, what is it?
A duality particle wave is a quantum phenomenon in which particles take on the characteristics of a wave, and vice versa, on certain occasions. Things that we would expect to always act like a wave (for example, light) sometimes behave like a particle. This concept was introduced by Louis-Victor de Broglie and has been experimentally demonstrated.
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Event
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 via telescopes. For each of them, we have information such as the position in the sky, the intensity, and so on. This information allows us to classify them. We are interested in having many events so that we can carry out statistical analysis a posteriori and draw conclusions.
Gamma Ray
Yes, we can!
Gamma rays are extreme-frequency electromagnetic ionizing radiation (above 10 exahertz). They are the most energetic range on the electromagnetic spectrum. The direction from which they reach the Earth indicates where they originate from.
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Lorentz Covariance
The privileges of certain equations.
Certain physical equations have this property, by which they don’t change shape when certain coordinates changes are given. The special theory of relativity requires that the laws of physics 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 the same in both cases.
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Microquasar
Below you will learn what a quasar is...well a microquasar is the same, but smaller!
A microquasar 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 jets and have an accretion disk surrounding a compact object (e.g. a black hole or neutron star) that’s very bright in the range of X-rays.
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Nebula
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. Many stars are born within them due to condensation and accumulation of matter. Sometimes, it’s just the remains of extinct stars.
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Particle Shower
The Niagara Falls of particles!
A particle shower results from the interaction between high-energy particles and a dense medium, for example, the Earth’s atmosphere. In turn, each of these secondary particles produced creates a cascade of its own, so that they end up producing a large number of low-energy particles.
Pulsar
Now you see me, now you don't
The word ‘pulsar’ comes from the shortening of pulsating star and it is precisely this, a star from which we get a discontinuous signal. More formally speaking, it’s a neutron star that emits electromagnetic radiation while it’s 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, which, by the way, is very beautiful.
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Quantum Gravity
A union of 'grave' importance ...
This field of physics aims to unite the quantum field theory, which applies the principles of quantum mechanics to classical systems of continuous fields, and 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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Quasar
A 'quasi' star
Quasars are the furthest and most energetic members of a class of objects called active core galaxies. The name, quasar, comes from ‘quasi-stellar’ or ‘almost stars’. This is because, when they were discovered, using optical instruments, it was very difficult to distinguish them from the stars. However, their 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 candy floss 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, with his theories of special and general realtivity, took Newtonian mechanics and made it compatible with electromagnetism. The first theory is applicable to the movement of bodies in the absence of gravitational forces and in the second theory, Newtonian gravity is replaced with more complex formulas. However, for weak fields and small velocities it coincides numerically with classical theory.
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