Night 3:In an Unknown Land
There are mysteries and then there are MYSTERIES
There are mysteries and then there are MYSTERIES
I’m not interested in astrophysics. I’m more into the most fundamental physics. Astrophysics is the description of the phenomena of what we see out there using the laws of physics. Fundamental physics tries to understand the physical laws that govern nature.
Looking for dark matter is one of the goals of fundamental physics because what is more fundamental than knowing the content of the Universe?
That little 4% is all that is possible for us to know for now. That's why there is a lot of fundamental research trying to unravel what the remaining 96% is made of. It's almost nothing...
I’m not so interested in knowing if there are interactions between protons in a supernova remnant (like CasA) or if the radiation that comes from them is produced by the electrons themselves. It’s not wrong to ask if the microquasar emits gamma radiation or not. But, what has really caught my attention, what I’m going to do is finding out what our universe is made of. Aren’t you surprised that we don’t even know that much about that yet?
What The matter and energy in our Universe is made from remains a mystery. Fundamental physics tries to solve it by following different paths, both experimental and theoretical.
Tonight, with the MAGIC telescopes, we’re going to observe the Perseus cluster.
All the calculations suggest that it has a lot of dark matter. And some theoretical models predict that dark matter colliding with itiself can produce gamma rays.
Let’s go! We cann’t let them get away!
Quim’s scientific notebook
Jeez… now that I know that someone else is going to read this book, I’ll have to try to write things down so that they make sense. The good thing is that when I read it again in a couple of weeks I may understand something!
Let’s see if the dark matter in Perseus generates gamma rays.
import numpy as np
import pandas as pd
import matplotlib.pyplot as pl
%matplotlib inline
We already have the libraries that we need. Time to read the data. Do you remember how to do it? If not, ask Alba when she’s got a minute. She’s very good at explaining these things! wants she explains herself very well!
#We read the files and give them a name
perseus_ON= pd.read_csv('data/EvtList_ON_Perseus_Other.txt', sep=' ')
perseus_OFF= pd.read_csv('data/EvtList_OFF_Perseus_Other.txt', sep=' ')
#How much data am I loading?
len(perseus_ON)
4111265
4 and a half million rows! No way is Excel going to be able to open that. Luckily Python can. And why do we have more and more data? Because every time we load it, we make it just a little more complicated.
Alba explained how to make the hadronness cut. But she already had the data a little prepared. She set it up so that she only had the ones who have a Theta Square less than 0.4. That’s not the case here, so, if I want to have a theta plot like Alba’s or Daniel’s, It is not my case, I need to also make a cut in Theta Square in addition to the hadronness one.
# 1 We define the cut variables had_cut and theta_cut
had_cut = 0.20
theta2_cut = 0.40
# 2 We select the data:
perseus_ON_cut = perseus_ON[(perseus_ON['had'] < had_cut) & (perseus_ON['theta2'] < theta2_cut)]
perseus_OFF_cut = perseus_OFF[(perseus_OFF['had'] < had_cut) & (perseus_OFF['theta2'] < theta2_cut)]
# Let me check how much data I have left
len(perseus_ON_cut)
310622
See? After the cuts we’re left with around three hundred thousand events. And now I can create the theta plot
pl.figure(1, figsize=(10, 5), facecolor='w', edgecolor='k')
Noff, ThetasOff, _ = pl.hist(perseus_OFF_cut.theta2, bins=40, histtype='stepfilled', color='red', alpha=0.5, normed=False)
Non, ThetasOn, _ = pl.hist(perseus_ON_cut.theta2, bins=40, histtype='step', color = 'blue',alpha=0.9, normed=False)
pl.xlabel('$\Theta^2$ [$grados^2$]')
pl.ylabel('Numero de Eventos')
pl.show()
It looks like Alba’s and Daniel’s *theta plot, right? But, actually, it’s not the same. Can you spot the difference? Mine is split into more sections. I have 40 and they only have 30. I have done it using “bin = 40” in the instructions:
pl.hist(CutHadOff.compressed(), bins=40, histtype=‘stepfilled’, color=‘red’, alpha=0.5, normed=False)
I can also change other things: the colour (color = ‘yellow’) or how the bars of the graph are painted (histtype = ‘bar’)
pl.figure(1, figsize=(10, 5), facecolor='w', edgecolor='k')
Noff, ThetasOff, _ = pl.hist(perseus_OFF_cut.theta2, bins=40, histtype='stepfilled', color='yellow', alpha=0.5, normed=False)
Non, ThetasOn, _ = pl.hist(perseus_ON_cut.theta2, bins=40, histtype='bar', color = 'magenta',alpha=0.9, normed=False)
pl.xlabel('$\Theta^2$ [$grados^2$]')
pl.ylabel('Numero de Eventos')
pl.show()
Which one do you like the most?
Now we just need to see how relevant all this is. At a quick glance, it seems that it’s not relevant at all, but let’s calculate the significance quickly.
Alba complained about Daniel, but she has also left some trapdoors… she’s got this function she uses to calculate the significance but she hasn’t told us what instructions it contains. Let’s solve it!
When you look at it, the calculation of the significance is very simple:
S = (N_on - No_off)/sqrt(N_on+N_off)
where sqrt (…) indicates the square root of what is inside the parentheses, which in Python can be written as:
(N_on+N_off)**(0.5)
To have N_on and N_off I simply add up the events from the first two divisions of the previous graph, which I have saved in the variables Non and Noff before.
EventosON=np.sum(Non[0:2])
EventosOFF=np.sum(Noff[0:2])
Significancia=(EventosON-EventosOFF)/(EventosON+EventosOFF)**(0.5)
print ("Eventos ON =", EventosON)
print ("Eventos OFF =", EventosOFF)
print ("Significancia =", Significancia)
('Eventos ON =', 18111.0)
('Eventos OFF =', 18025.0)
('Significancia =', 0.45240605872906037)
As I said: 0.45 sigmas, which means that we can’t see any gamma rays coming from the dark matter that is in Perseus. But does this mean that there is no dark matter there? We’ll be able to see that soon, and to get ready for it, I have also noted the number of events ON and OFF.
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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