Well, now that we have covered all of the basics of the atom, its structure and, most importantly, the nucleus’ stability, we can look into what happens when an atom is unstable, or how most atoms are radioactive! 

PS. Link to part 1 if you need a reminder: PART 1

Radioactive decay and radiation

Back in the 19th century, X-rays, a type of electromagnetic radiation, were discovered. After the monumental discovery, a scientist Henry Becquerel was working on some experiments with a, then unbenknownst to him, a radioactive compound. He conducted the following experiment: he put the compound in a small tray and put a piece of black paper in front, and left it just like that for a while. After some time, he noticed that the compound left marks on the sheet of paper, which were quite visible.

He didn’t know why or how it worked, but we now know this is radioactive decay. The term was coined by Marie Curie, who discovered radium and polonium, two radioactive elements.

A radioactive element is a heavy atom, where the strong nuclear force can’t keep the atom together, or it is excited and contains too much energy. To minimize its energy and regain stability, it releases radiation in the form of 4 types of radioactive decay. In this process, our radioactive atom transforms from one element into another, removing particles that change the chemical makeup of the atom. Radioactivity and decay are the helpers after the war was lost on the stability of the nucleus. When things start falling apart, they pick things up, and save most of the nucleons. By lessening the tension between the nucleons, removing some built-up energy, radioactive decay proclaims peace in the atom.

Disintegration chains

Most commonly, the resulting atom is not perfectly stable during an unstable atom decaying via radioactive decay. So, it keeps on decaying until we reach a stable isotope in a normal disintegration series. However, at specific points, our element can decay by 2 types of radioactive decay, and which branch it will go in a branched disintegration is a probability based on the likelihood of each branch occurring based on experiments!

Isotopes are atoms of the same element with different numbers of neutrons. Neutrons are essential to keeping an atom stable, but they are also a downfall of its stability. An isotope with too many neutrons becomes unstable and can decay. At the same time, an isotope with too few neutrons aggravates protons, rendering the whole atom unstable. However, isotopes are not the only atoms with different radiation or stability levels.

Isomers are atoms of the same element with differing energy levels. As I mentioned earlier in this post, some atoms are radioactive due to high amounts of energy, which makes all the particles jittery. Releasing that energy changes the energy state of the atom into an isomer while still staying the same element. So, how do elements decay exactly?

Types of radioactive decay

Alpha decay

Alpha decay occurs when an unstable nucleus releases 2 protons and 2 neutrons. The parent nucleus decays into a child nucleus and an alpha particle made of 2 protons and 2 neutrons. The alpha particle matches a standard helium nucleus.

How did we discover that? Well, obviously, there was a genius experiment involved. A compound suspected of emitting alpha particles was put inside a tube that had very thin walls, allowing the particles to pass through. That tube was in another tube with thick walls, not allowing the alpha particles to pass through. Between the 2 tubes, electrons were freely floating around. After some time passed, scientists found that the space between the tubes was now filled with helium!

So they knew that the particle contained protons, and subsequently, neutrons were discovered as slightly heavier particles with no charge. During the release of an alpha particle, the element loses 2 protons, becoming an entirely different element in total.

Alpha decay is the dominant way that elements above proton number 83 decay.

Why is this? Because these atoms have too many neutrons and protons to keep stable, hence releasing alpha particles diminishes both neutron and protons numbers, stabilizing the atom.

Beta decay

Beta decay occurs when an unstable neutron converts into a proton and releases an electron and antineutrino, as discussed in the section on neutron instability. This way, the fundamental element also changes, as in alpha decay. This type of beta decay is called beta minus decay since a neutron transforms into a proton. Why does this decay occur? When the number of neutrons against protons is too high, this decay increases the number of protons. It decreases the number of neutrons, making the ratio more manageable for the atom.

However, there is another type of beta decay. It happens when the number of neutrons against protons is too low! So, here, a proton transforms into a neutron, similar to the previous type. One of the up quarks inside a proton turns into a down quark, mediated by our boson particle. It quickly decays into a positron and a neutrino. A positron is the arch-version of an electron. It has the same mass and spin but an opposite charge. When a positron and an electron come into close contact, they annihilate each other! We usually dub the positron as antimatter (more about matter and antimatter in another post).

Wait, I think I forgot to explain a particle… Ah, it was the neutrino! It is a crucial particle to beta decay, and neutrinos are actually found everywhere in the universe!

The elusive neutrinos

Neutrinos are particles with almost no mass (extremely close to 0) and almost no charge. They are usually produced in very violent astronomical situations like in the cores of stars, in supernova explosions, orbiting black holes, etc. Neutrinos are specific in their nature because they interact with matter extremely rarely, making them the most abundant particle in the universe! However, this also makes their detection extremely difficult.

These elusive particles were first theoretically postulated by physicist Wolfgang Pauli in the 1930s. Energy and angular momentum weren’t conserved in the beta decay reactions, and both need to be conserved if the universe would exist! So, Pauli proposed that there must exist a particle which doesn’t interact with other particles and is neutral in terms of charge, everything would be conserved! And so, in 1955, the first antineutrinos (remember, the antimatter version of the neutrino) were detected in a nuclear reactor. 

Detection of neutrinos

How were they detected? As we know, in beta decay, an antineutrino is released. Those antineutrinos passed through a liquid in the detector where if a antineutrino interacted with a proton, it would produce a positron (antimatter version of the electron) and a neutron. The positron quickly connects with the electron, and sine one is antimatter and the other matter, they are quickly annihilated, but in the process they release gamma waves, and that is what scientists detected!

Figure 5: detection of antineutrinos

However, the first natural neutrino was detected in 1965. Deep in a mine, scientists put a large tank filled with perchloroethylene, a chemical compound that contains Chlorine 37. When neutrinos travel from the sun all the way to Earth and penetrate into the tank, some interact with the chlorine to produce Argon 37. And, the researchers detected Argon 37! But, there was a problem.

The solar neutrino problem

The researchers measured only a third of the neutrinos which would theoretically come from the sun. Scientists knew that there are 3 types of netrinos: electron neutrinos, muon neutrinos and tau neutrinos. Like quarks, each has its specific properties. This is known as the solar neutrino problem. However, scientists think they have solved the problem. They discovered that neutrinos oscillate a lot between types, so we only receive a third of the neutrinos from the sun, because other neutrinos convert to other types which don’t reach the detectors. These discoveries infer that neutrinos have slight mass, even though thus far it was thought they were massless. 

Scientists actually think that there might even be a fourth type of neutrino which could explain dark matter! But, that is for a future post when we discover something, since up until now everything has just been theoretical 

Gamma decay

Gamma decay is a type of radioactive decay where no particle is emitted and the parent radioactive atom stays the same element. The parent atom emits a gamma ray, or a super high energy photon. This lowers the energy levels of the parent atom, rendering it more stable.

Electron capture is a type of decay where a proton inside the nucleus “captures” an electron which is closest to the nucleus, transforming into a neutron and releasing a neutrino. Since there is now an empty spot for an electron in the innermost orbital, an electron from a higher energy level comes in, during the process releasing an X-ray.

As we can notice from the 4 types of decay, the first two (alpha and beta) correspond to isotopes, and how different elements decay into different isotopes of different elements. Meanwhile, the third type (gamma) corresponds to isomers, transforming into the same element of a different energy level.

The life of a radioactive atom

Nothing lasts forever. The principle applies especially to radioactive elements, which decay after a while to preserve as much as possible, peace between nucleons. But, there is always a defined time until a peace treaty is resolved. This time is called a half-life of a radioactive atom. It is the amount of time that it takes half of all the radioactive samples in the population to decay into more stable variants. The following graph depicts the half-life curve of a radioactive atom.

As you can probably infer, the half-life function is an exponential function, meaning that as we move by one unit (a half-life), half of every consecutive part of the original population of the radioactive element decays. The shorter the half-life, the more radioactive the element is!

Nuclear reactions

After discussing so many properties of nuclei, let’s put it all together, and analyze 2 nuclear reactions where they bring life and opportunities, but also death and destruction.

Nuclear fission

So, as you can imagine, during radioactive decay, energy is released. As a atom decays into a parent and daughter element, particles or energy is released, and part of the mass released during the decay turns into energy. As uranium decays, it can release a very large quantity of energy if enough grams of uranium decays naturally. However. There is another way.

In an experiment in 1938. scientist Lise Meitner fired barium nuclei at uranium nuclei, and he couldn’t separate the barium from the uranium anymore. No flood of radioactive particles. It appered that the uranium nucleus was split in half. This is the first evidence of nuclear fission! This process released much, much more energy than natural radioactive decay, so humans used nuclear fission in nuclear reactors and weapons like the nuclear bomb.

Figure 8: the process of nuclear fission

How does one aquire enough energy from these processes to power a nuclear reactor or a bomb? Well, once one neutron bombards one uranium atom, it splits and ejects “lost” neutrons which hit other uranium atoms and in this fashion a chain reaction is induced, either in a controlled (nuclear reactors) or explosive (bomb) manner.

But, why doesn’t nuclear fission just occur naturally (in most cases)? Well, you can imagine every radioactive decay as an “energy path” which can contain bumps and hills. When radioactive decay occurs, the bump is so small that very little energy is required to begin the reaction. However, the bump for fission is much, much higher, so particles literally need to smash into one another so enough kinetic energy is converted so nuclear fission can occur. 

Nuclear fusion

The second type of nuclear reaction is nuclear fusion! This type of reaction is the very reason why any of us are alive on Earth today and why the whole universe exists in such wonder as today.

Nuclear fusion is a nuclear reaction where particles fuse together to form more complex elements. So, it is the opposite of nuclear fission. As of now, fusion is not yet possible on Earth on a scale which would produce energy, but scientists are working hard on it!

The energy of the stars

The combining of smaller particles to form different elements releases less energy that nuclear fission, however on very large scales, meaning there are massive amounts of particles, the energy increases drastically! The Sun is around 1.99 * 10³⁰ kg. Each gram contains 4.5 * 10²³ protons! Now, not every bit of the Sun can be used for fusion, only the very core. So, our Sun has around 10 * 10⁹ years to live on its supply of protons. The energy of the Sun produced by fusion is so great, one hour of fusion can supply humanity for around 2.3 billion years! That is insane. Due to our current technological standing, we aren’t able to reproduce fusion on Earth or even capture a significant fraction of that energy, but someday we just might.

Stars live by fusing elements together. We start off with hydrogen, then helium, and we progress on to heavier elements all the way to iron. Lower elements (like hydrogen, helium,…) when fused together produce more energy than higher elements (carbon, oxygen,…), and iron is the final element in the fusion cycle of stars. Why? Because Iron is too heavy to produce more energy, rather it consumes energy and it can’t be fused further in the cores of even the most massive stars. 

The fundamental fusion process is called the proton-proton chain. Let’s explore it. 

Proton-proton chain

So, in a star’s core, temperatures are extremely high (in the Sun its around 15 million degrees Celsius), and atoms aren’t kept together. The individual particles and nuclei of atoms are floating around in an ionized state called plasma. Plasma can be thought of as another state of matter with its own unique properties.

So, 2 lonely protons collide together to form a deuteron, which is a heavier version of hydrogen, made of a proton and neutron. In the process, a positron and electron neutrino are released (beta plus decay, the proton turned into a neutron). This is where we find our electron neutrinos from the Solar neutrino problem! Now, the deuteron fuses together with another straggling proton. Now they form a Helium 3 nucleus, containing 2 protons and a neutron, releasing a gamma ray in the process. Finally, another Helium 3 nucleus approaches (formed by the same process described so far), and together they form a proper Helium 4 nucleus, containing 2 protons and 2 neutrons. In the process 2 protons are released, ready for a new proton-proton chain. 

Figure 9: proton-proton chain

And with this process, every object and structure you see in the universe was created. 

And, we end at the beginning. With quarks coming together in the early universe, forming protons and neutrons, the universe cooling down enough to form atomic nuclei, the battle between the nucleons fought every single moment, when electrons were finally able to join the nuclei and form atoms, which in turn created every beautiful thing around us.

I hope you learned something new about the wonderful universe around us, and to never underestimate the complexity and power of something so small as the nucleus.

REFRENCES

• Chemistry The Central Science by Theodore L. Brown H. Eugene LeMay Jr Bruce E. Bursten Catherine J. Murphy Patrick Woodward Matthew E. Stoltzfus, Pearson, 14th edition, chapter 21 on Nuclear Chemistry
• Understanding physics Volume 3 by Isaac Asimov, Barnes&Noble books, 1996, chapters 7, 8, 9, 11, 12, 14
• University Physics with Modern Physics by Hugh D. Young, Roger A. Freedman, A. Lewis Ford, Pearson, 15th edition, chapter 43
• https://www.scientificamerican.com/article/what-is-a-neutrino/
• https://www.space.com/what-are-neutrinos
• https://neutrinos.fnal.gov/whats-a-neutrino/
• https://www.youtube.com/watch?v=lUhJL7o6_cA

The post A Deep Dive Into The Atomic Nucleus: Part 2 appeared first on Adventures in Astrophysics.

In this series, we are tackling the nucleus of the atom, or nuclear physics, a branch of physics that tries to investigate the secrets of the nucleus.

We begin with part 1: the discovery of the atom, the nucleus, the properties of the subatomic particles, and the structure and stability of the nucleus. Part 2 will discuss everything related to radioactivity and radiation, half-lives, and nuclear reactions like fission and fusion. We will also discuss exciting particles called neutrinos!

Everything begins and ends here. Our world began with the nucleus: the universe’s atoms arose from nuclei in a sea of particles. Our civilization’s ultimate demise could be from splitting the nucleus — the end at the beginning.

The discovery of the atom

So, we all know what atoms look like now, right? There have been many models for atoms in the past, starting from ancient Greece, when Democritus described the atom as an indivisible particle of which everything around us is made of. While this was just speculation, he was proven to be on the correct path many years later.

The plum pudding model

Then, John Dalton proposed the atom’s existence based on his experiments with gasses. He discovered that different types of atoms exist and make up compounds we can find in everyday life.

After establishing the atom’s existence in the 19th century, physicist J.J. Thompson discovered the electron using cathode rays (More about electrons and their role in physics and chemistry in another post). He formed the plum-pudding model,

which is basically just electrons floating around in a positively charged sphere.

The famous gold foil experiment

Soon after the electrifying discovery, scientist Ernest Rutherford completed his famous gold foil experiment. He set up a source of alpha particles (more about them in part 2) to shoot them toward a very thin sheet of gold foil. Around the gold foil, a circular fluorescent sheet was placed so the alpha particles would be visible when they hit the screen. When the particles were shot through the gold foil, some veered off at extreme angles. This showed that the atoms inside the gold foil contained positively charged nuclei (since alpha particles were known to be positively charged). And just like that, the nucleus was discovered.

The alpha particles didn’t all end up directly behind the entry point to the gold foil because of positively charged nuclei in the atoms! We know that alpha particles are positively charged. When interacting with a positively charged nucleus, the opposite charges repel each other. Suppose the alpha particle comes in close enough contact with the nucleus. In that case, the high charge of the nucleus furiously repels the alpha particle, causing it to deflect at very large angles.

What was the nucleus made of?

But it wasn’t known that the nucleus contained protons and neutrons. Since neutrons weren’t discovered, scientists first thought it was made of protons and electrons. This soon proved wrong when the nucleus’s supposed spin (more about spin in a future article) didn’t match experiments, and the nucleus was too heavy to be made of protons and electrons. Thus, we found a heavy particle with no charge: neutrons.

So, the nucleus was made of protons and neutrons and was super dense compared to the size of the atom. However, it wasn’t known why electrons didn’t collapse towards the nucleus. It seems logical, right? The positive charge of the protons in the nucleus is attracted to the negative charge of the electrons orbiting the nucleus. And yet, atoms exist. This is because of some super weird properties of electrons in the realm of quantum mechanics (which deserve a special post).

The planetary model

Neils Bohr came in in 1913 with his planetary model of the atom. He proposed that electrons orbit the nucleus in shells. Each shell is in a specific layer around the nucleus and can contain electrons of certain energy levels and different spins. The further away the electron is from the nucleus, the more energy it has, and vice versa. While this model was very successful then, the more we learned about the atom and mainly electrons, the more inconsistencies were found, which had to be fixed.

As of our most recent knowledge, our understanding of electron behavior has changed. We realized that an electron’s path can’t be strictly defined around the nucleus, only the probability of where the electron is. This is why we have electron clouds instead of distinctly defined “paths” of electrons.

Properties of subatomic particles

Contrary to popular belief, not all subatomic particles are stable.

Contrary to popular belief, not all subatomic particles are stable.

Electrons are leptons, particles that aren’t influenced by strong interactions. In other words, they aren’t affected by the strong force. They are very stable, too. They can’t break down since they aren’t made up of any other particle.

The nucleons

Protons are made of 3 quarks: 2 up quarks and one down quark, tightly bound together by gluons (more about them later). Quarks are indivisible particles with a slight charge and come in different flavors! They can be up, down, charm, strange, top and bottom. And even though the names sound weird, the only differences between these types are the mass and charge. Only up and down quarks are found in ordinary matter. In contrast, the rest of the quarks are produced in very high-energy collisions and last a very short time. Since they are so small, it is hard to conduct research with them, which is ongoing.

As of our current understanding, protons are either very stable particles or have an extremely long half-life. (more about that in part 2).

Meanwhile, neutrons are made of 2 down quarks and one up quark. And they are unstable in the long term!

When neutrons find themselves in the nuclei of atoms, they are stable because the gluons keep the quarks in the same flavor. Gluons are massless particles and carriers of the strong force. They keep protons and neutrons tightly bound. However, nothing retains the quarks from changing flavors if a neutron is isolated! 

So, one of the down quarks in a neutron turns into an up quark, mediated by a boson. This particle mediates the weak force responsible for quark behavior. This boson is quite unstable and quickly decays into an electron and an antineutrino (more about neutrinos in part 2). The neutron transforms into a proton with the electron and the antineutrino released.

Since neutrons aren’t the most stable creatures (along with protons on some occasions), does that mean the nuclei fall apart?

Stability and structure of the atomic nucleus

The central premise of radioactivity and radiation is that the nucleus of our atoms is unstable (more about that in part 2). So, how are nuclei structured, and what keeps them stable?

The nucleus contains neutrons, which have no charge, and protons, which have a positive charge. Due to charge, protons will repel each other furiously, meaning the atom cannot exist! And yet, it does. How come?

Neutron vs. proton ratio inside the nucleus

The neutrons act as guards for the protons, essentially keeping them in check from falling apart. The strong nuclear force is an attractive force that is extremely strong, much more than the electromagnetic force, which enables the “opposite charges repel” law. However, the larger the nucleus, the more neutrons are required to keep the protons from repelling each other too far since there are more and more of them. 

After a while, the ratio of neutrons vs. protons isn’t 1:1 anymore since more neutrons are required to keep things in balance. The graph below shows the stability strip or the strip of atoms where the ratio is good enough for the nucleus to stay stable. Too many neutrons, too few neutrons vs. protons, or simply too many neutrons and protons can lead to instability.

All atoms above proton number 83 are unstable and radioactive.

Binding energy

Another factor that keeps things together is binding energy. This is the energy necessary to keep the nucleus bonded together. The more protons and neutrons in the nucleus, the higher the binding energy until a certain point. Afterward, the energy starts declining, meaning it is easier to break the bond. This is why very heavy atoms are more unstable. The following graph depicts the bonding energy of atoms:

Why does the graph start decreasing after nickel? Because the more nucleons (protons and neutrons) there are, the larger the atom’s radius. Since the radius increases, the strength of the strong force begins to dwindle because it acts only on minimal distances. As the force weakens, keeping the straggling nucleons at the boundary of the nucleus bound becomes harder.

An interesting fact about binding energy is that if we take the individual masses of all the protons and neutrons in the nucleus, add them together, and compare that sum to the actual experimental mass of the nucleus, we see that they aren’t the same!

The sum is greater than the actual mass! How is this possible? Due to Einstein’s equation, E=mc², mass and energy are interchangeable. So, part of the masses of the nucleons are converted into energy, which keeps everything together.

So, how is the nucleus structured so that binding energy works out? There are 2 famous models: the liquid drop model and the shell model.

Liquid drop model of the nucleus

This model infers that all nuclei are of approximately the same density (which makes intuitive sense) and that every nucleon in the nucleus is kind of like a “drop of liquid.” The whole nucleus is like a liquid, so we can define the individual nucleons as liquid particles in liquid matter. This model can estimate a nucleus’s total bonding energy and accounts for processes like nuclear fission.

Shell model of the nucleus

This model says the nucleus is like the electron cloud: it contains shells of differing energy levels where protons and neutrons can be with different spins, based on the Pauli exclusion principle. This principle states that no two particles can be in the same state in the same space (orbital or shell). So, in each shell of our nucleus, protons and neutrons cannot be in the same state, meaning they can’t have the same spin.How does this work?

As scientists observed many, many different isotopes of elements, they noticed something very curious. If nuclei had even numbers of both protons and neutrons, they would be much more stable than even-odd, odd-even, and especially odd-odd combinations. A possible reason for this even-even preference might be because the strong force prefers pairs of neutrons and protons! This means that they are bonded tighter and, hence, more stable.

So, this means the nucleus has some structure, doesn’t it? If things are this ordered? A Polish-American scientist, Maria Goeppert-Mayer, created the shell model, which says that the nucleus is composed and contains shells where nucleons reside. Sometimes, isotopes are exceptionally stable or common if they have the following magic numbers of nucleons in the nucleus: 2, 8, 20, 50, 82, and 126.

In reality, neither model is absolutely correct, and we use a combination of both models for our calculations.

Summary of nuclear stability

Now that we know about all the components of nuclear stability, let’s put it all together. Nucleons are kept together by the strong force, which grows weaker the larger the nuclei become. It battles against the formidable electromagnetic force, pushing the protons away from each other due to their charge. However, neutrons help out the strong force, keeping the protons at bay. But, sometimes, there might be too little help (too few neutrons), the nucleus collapses, or too much help (too many neutrons), and everything falls into chaos. And sometimes, there is simply too much to take care of, and the strong force must admit defeat.

However, there are magical times when things work out great. There are magic numbers of nucleons in the nucleus shells, keeping it more stable than ever. But, no 2 nucleons are allowed to have the same intrinsic spin, so they must differ between every shell of the nucleus. The binding energy is the last component in the war of the nucleus. It takes away from the nucleons, converting their mass into energy and keeping them bonded. But, its powers are not infinite, and beyond a certain point, too much is too much, and the binding energy starts to decline. These factors work night and day to keep the atom together and the whole universe alive.

But what happens when this war is lost? When all the forces that attempt to keep the atom in check give in, and instability reigns the atomic nucleus? Well, a little something called radioactive decay comes in after the war is lost. More about that in part two…

PS. Link to part 2 coming soon!

REFRENCES

• Chemistry The Central Science by Theodore L. Brown H. Eugene LeMay Jr Bruce E. Bursten Catherine J. Murphy Patrick Woodward Matthew E. Stoltzfus, Pearson, 14th edition, chapter 21 on Nuclear Chemistry
• Understanding physics Volume 3 by Isaac Asimov, Barnes&Noble books, 1996, chapters 7, 8, 9, 11
• University Physics with Modern Physics by Hugh D. Young, Roger A. Freedman, A. Lewis Ford, Pearson, 15th edition, chapter 43
• https://www.youtube.com/watch?v=lUhJL7o6_cA
• Photo by NASA on Unsplash -> cover photo

The post A Deep Dive Into The Atomic Nucleus: Part 1 appeared first on Adventures in Astrophysics.

Our universe is a vast place filled with many different things, and for everything to be organized and functioning, there have to be specific forces at work. That’s why we have the four fundamental forces of the universe governing how everything works. They are:

• gravitational force
• electromagnetic force
• weak force
• strong force

Our universe is split into two hemispheres. One half is the macroscopic universe, which focuses on the stars, galaxies, planets, and nebulae. The other half focuses on the extremely small, like atoms, protons, quarks, and gluons. This article will learn about the forces that govern each hemisphere. Let’s start with the most apparent force we interact with daily. Gravity.

What comes up must come down…right?

…Not quite. If we throw something fast enough, say 11.2 km/s, it definitely will not come down. However, that is not the point. Gravity is a force that acts on any object that has mass, attracting other things with a smaller mass toward it. So the more mass an object has, the stronger field of gravity the object has. Like, the whole universe is like a giant rubber sheet, stretching and changing its shape based on the things moving on it. However, even though gravity makes stars and planets and basically everything significant in the universe possible, it is the weakest force. How can this be? Black holes are the objects with the most gravity in the universe, and they seem pretty scary. Look at how easy it is to fly, walk and throw things on Earth! It is effortless to defy gravity. 

Electricity + magnetism

The electromagnetic force is pretty important. It keeps atoms and molecules with opposite charges: the same charges repel, and opposite charges attract. Using this simple rule, it has managed to keep stuff together and make chemical reactions possible. This is because the particles have an electromagnetic field surrounding them, enabling these interactions. Also, electromagnetic waves make up light! Although light is dual, made up of particles called photons that are massless and carry energy, electromagnetic waves with different wavelengths represent different types of light. Also, this force enables the world to work the way it does.

For example, all objects would go straight to the ground without it because nothing would stop them. If we put a book on a table, it doesn’t go through the table as gravity would want. It stays on top because the particles in the book repel the particles in the table, and the book is kept on the table—yet another example of how gravity is weak. 

keeping atoms friendly

The next force is as essential as all of these forces, and it is called the strong force. Its primary purpose is to keep the atom’s nucleus together and keep the protons from escaping towards the electrons. As the name suggests, it is the strongest force in the universe, although it acts at tiny distances. It is 6 thousand trillion trillion trillion times stronger than gravity. That is many, many times stronger than gravity. But, contrary to popular belief, this force gets weaker the closer the protons and neutrons are.

Another one of its purposes is to keep quarks in check. Quarks are even smaller particles than protons, making up protons and neutrons. Gluons are particles that transmit the strong force across space, essentially “gluing” the quarks together, which in turn glues the protons together. If we try to pull quarks apart, so much energy gets spent, and we create new quarks since E = mc^2! Although this force is powerful, electrons do not experience it; only protons and neutrons. 

the force of decaying matter

The last force on our list is the weak force or the force that governs quarks and decay. There are six types of quarks in the universe: up, down, strange, charm, bottom, and top quarks. And the weak force changes the type of the quark. This process is called particle decay, and it also applies to larger particles like protons and neutrons. If two particles hit each other hard enough in a collision, they can exchange particles called bosons and change their type. 

And that’s it! These four forces govern all the interactions in the universe, making everything you see around yourself possible. However, scientists are disputing a fifth force: dark matter. It is an invisible force with an invisible particle, and we don’t know much about it. 

Another goal for physicists is to create a unified theory of everything, or they are trying to unify the four forces into one force. So far, unification was done with the electromagnetic and weak force, but gravity is the force that keeps messing things up. Hopefully, we will find a way to unify everything and make sense of the universe even more in the future. 

Other cool posts

The post The 4 fundamental forces of the universe appeared first on Adventures in Astrophysics.

When lecturing physics, it is important to teach kids how to do physics, why things are the way they are and help them appreciate the wonderful world around us. It is with my great pleasure to announce the beginning of a series of lectures, resources and presentations for physics classes in elementary school, grades 7 and 8, starting with this presentation about what physics is.

I personally love physics, and I think that it provides an amazing view of the world from the tiniest constituents in quantum physics, to the grand scale of the universe, combining astronomy, and many areas of physics.

What does this presentation include?

In this presentation, you will learn everything you learn in your first physics class of the year, and get answers to these questions:

1. What is physics?
2. What areas does physics study?
3. What are the physical properties of objects?
4. What do physicists work on?
5. What is the scientific method?
6. How do I conduct good experiments?
7. How do I solve physics problems?

Also, all of these presentations will include (including this one):

• Fully researched and written text
• Images, illustrations and explanations
• Cool and interactive design
• Discussion points
• Experiments and projects
• Review questions from the day
• Examples, problems, all solved and explained

What this presentation is about

This presentation is meant for kids to explore themselves, or more importantly for teachers around the world to use in their physics classes, to introduce their students to the waters of physics. I do hope educators and teachers enjoy this presentation and use them in their classes, and also that the students themselves enjoy it. I put a lot of hard work into this and I hope I made someones day a little better by explaining them physics.

Don’t worry though, this isn’t the only presentation! Next up: we are covering area, volume, mass and temperature, the basic properties of matter. After that we will look into density, one value that differentiates objects from one another. And with that, our introduction is done. We dive into the waters of physics head on and explore our wonderful universe, one thought at a time.

And on a last note: all of this is free for everyone to use. Just make sure to credit the author if used for a public lecture or similar, but in class use without restrictions. And if you have any questions, about physics, astronomy, maths, science, you name it; you can always ask in the comments below.

Happy learning!

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The quiz!

If you want to learn more about particular constellations, check out these 3 posts about Ursa Minor Ursa Major and Cassiopeia.

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Every time I look up into the night sky in winter, the first constellation that catches my eye is Cassiopeia, the Queen of Ethiopia. Such a simple constellation represented as a W. Still, it holds so much knowledge and is one of the rarest stars in the galaxy. What will the queen tell us?

Mythological origins

Cassiopeia, or the Queen of Etiopia, was married to Cepheus, the King of Ethiopia, and they had a daughter, Andromeda. Cassiopeia loved to boast about her beauty and excellence and said she was more beautiful than all the sea nymphs called the Nereids. The Nereids were displeased, and they forced the king of the sea, Poseidon, to ravage Cepheuse’s kingdom. He obliged, being married to a Nereid.

He set free a sea monster called Cetus (the great whale, also a constellation) to ravage the kingdom. Trying to save their kingdom, Cepheus and Cassiopeia consult an oracle, saying they have to sacrifice their daughter to save the kingdom. They did just so, tying her to a rock in the middle of the sea. She awaits her demise. Cetus was approaching, readying himself to devour her. At that moment, Perseus, the strong hero, who was flying on his horse, Pegasus (also a constellation and Perseus), swopped down to save her. 

Of course, Perseus and Andromeda fell in love and got married. However, at the wedding, Andromeda’s suitor showed up and proclaimed that only he had the right to marry Andromeda. Naturally, there was a fight, with Perseus greatly outnumbered. He drew out his only chance of survival. He pointed to Medusa’s head, the head of a horrible sea creature, which turns anyone looking at it into stone. The suitor’s army was turned to stone, and unfortunately, Cepheus and Cassiopeia didn’t look away in time. And, Poseidon placed Cepheus and Cassiopeia in the sky. However, Cassiopeia was condemned to circle the north pole forever. Moreover, she spends half of the time upside down as a punishment for her boasting and selfishness. 

Other cultures

Her story changes according to different cultures. Her boasting and selfishness come from Greek mythology, as with most north hemisphere constellations. In Arab culture, Cassiopeia and a few stars from Perseus and Andromeda represent the Camel. In Persia, she was a queen holding a staff with a crescent moon, wearing a crown, and having a 2 humped camel. Meanwhile, in Chinese astronomy, Cassiopeia was represented as the Purple Forbidden enclosure, the Black Tortoise of the North, or the White Tiger of the West. In the tribe of Lapps, Cassiopeia forms an elk antler, and the Chukchi in Siberia saw Cassiopeia as 5 reindeer stags.

But Cassiopeia doesn’t hold only divine mythological greatness. Her structure and position in the sky greatly matter. It is the 25th biggest constellation, and it is circumpolar, which means we can see it all year round. So let’s take a spin on its stars, see what they have to say. 

Schedar – α Cassiopeiae

Schedar is an orange giant with a K spectral type. It is 228 light-years distant and is a suspected variable star. However, it hasn’t shown signs of variability since the 19th century. Schedar is nearing its end, its photosphere has expanded, and it is getting ready to die. Its name, Schedar, translates to “breast,” which tells us that it denotes the position of Cassiopeias heart. 

Caph – β Cassiopeiae

Caph is a subgiant or giant star with a spectral type F, a spectral class above our sun. It is approximately 54.5 light-years distant. It is also in the process of dying, a soon to become red giant. Its meaning in Arabic is “palm,” marking Cassiopeia’s hand. 

Cih – γ Cassiopeiae

Coincidentally, it is the brightest star in Cassiopeia, even though the alfa star should be the brightest. It is a blue B star and about 610 light-years distant. Cih is a Gamma Cassiopeia variable star, which exhibits irregular variations in brightness since it rotates very rapidly and has a bulge around the equator. A a result, the lost mass from the spinning orbits the star, which causes fluctuations in luminosity. 

Rho Cassiopeiae – the rarest class of stars in the galaxy

Rho Cassiopeiae, a yellow hypergiant, the rarest class of stars, only 7 found in the galaxy. Remember, there are a lot of actors in the galaxy. Its spectral type is the same as our sun, G2, with slight differences. It is appr. 11650 light-years distant and one of the most luminous stars ever known. The star probably went supernovae, but its light hasn’t yet reached us. Currently, Rho Cassiopeaie is like Schrödinger’s cat: neither alive nor dead. 

Deep-sky objects

What about the beautiful nebulae and clusters surrounding Cassiopeia? 

M52 

M103 – the last object in Messiers catalougue

Bubble nebula – NGC 7635

Cassiopeia A – supernovae remnant

Pacman nebula – NGC 281

White Rose Cluster – NGC 7789

So, Cassiopeia contains one of the rarest stars in the galaxy, beautiful nebulae, clusters, and rich mythological history. So you tell me: is Cassiopeia as beautiful as she boasts of being?

Resources:

Constellation guide: https://www.constellation-guide.com/constellation-list/cassiopeia-constellation/

EarthSky: https://earthsky.org/constellations/constellation-cassiopeia-the-queen-lady-of-the-chair-how-to-find-history-myth/

Astro Backyard: https://astrobackyard.com/cassiopeia-constellation/

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Intriguing properties of Fibonacci’s numbers 

Theorem 1:

Sum of three consecutive Fibonacci’s numbers divided by two equals the biggest of three consecutive numbers. 

Let’s start with one straightforward property of Fibonacci’s numbers. Suppose we were two take any three consecutive Fibonacci’s numbers and divide their sum by two. In that case, we will get the biggest of those three numbers. For example (8 + 13 + 21) / 2 = 42 / 2 = 21. This can be easily proven by rewriting these three numbers as, respectively, n, m, and n + m. When we add them together, we get 2n + 2m divided by 2 equals n + m, the biggest of the three numbers. 

Theorem 2:

If we take four non-zero, consecutive Fibonacci numbers, the difference between the first and fourth product and the second and third numbers will be one. 

As an example 2 × 8 – 3 × 5 = 1 and 3 × 13 – 5 × 8 = -1. More generally, we can write these numbers, respectively, as n, m, n + m and 2m + n so we get | n × (2m + n) – m × (n + m) | = 1. Now, this is slightly trickier to improve since the proof includes induction. So let’s start by proving this is true for the first numbers in the sequence: 1, 1, 2, and 3. 

1 × 3 – 1 × 2 = 3 – 2 = 1 

When we have done that, we can move to the next step. Let’s assume this property holds for all n, where n is the index of the first of four consecutive numbers. That means that: 

| n × (2m + n) – m × (n + m) | = 1 

| n2 + mn – m2 | = 1 

The final step is proving that if the theorem is true for n, it is also true for n + 1, or in other words n implies n + 1. Next four consecutive numbers are m, n + m, 2m + n, 3m + 2n. For them we need to prove that: 

| m × (3m + 2n) – (n + m) × (2m + n) | = 1 

| 3m2 + 2mn – 2mn – n2 – 2m2 – mn | = 1 

| m2 – mn – n2 | = 1 

If we compare this equation to the equation | n2 + mn – m2 | = 1 for which we assumed is accurate, we see that pluses and minuses are switched. So if the first expression equals 1, the second is equal to -1 and vice versa. And by this, we proved the theorem. 

Theorem 3:

For any three consecutive non-zero numbers, the difference between the product of two outer numbers and the square of the middle number is one. 

For example, 2 × 5 – 32 = 10 – 9 = 1 and 3 × 8 – 52 = 24 – 25 = -1. We can prove this theorem by the induction method since it is similar to the previous theorem.We know the statement is true for n = 1 because 1 × 2 – 12 = 2 – 1 = 1, so let’s assume the property holds for numbers n, m and n + m. That means that: 

| n × (m + n) – m2 | = 1 

| n2 + mn – m2 | = 1 

Now let’s move to the third step and prove that n → n + 1. Now, we have numbers m, m + n and 2m + n so that would mean: 

| m × (2m + n) – (n + m)2| = 1 

| 2m2 + mn – n2 – 2mn – m2 | = 1 

| m2 – mn – n2 | = 1 

Same as in the second theorem, we see that pluses and minuses in the second equation switched, so the result will negate the result of the first equation. And by this, we proved the third theorem. 

Fun Combinatorics Task with Fibonacci numbers: 

Question: 

And for the end, here is one exciting combinatorics task. You have a table with dimensions 1 x m. You have to fill that table with squares dimension 1 × 1 and rectangles of dimensions 1 × 2. As an example, if m = 5, one way of arranging squares and rectangles in the table is: 

Let Jm (m > 2) be the number of different ways you can arrange squares and rectangles in the table dimensions 1 × m. Then, prove that Jm = Jm – 1 + Jm – 2. 

Solution: 

Let’s take a look into the possible beginnings of the 1 × m table. First, we can start with a 1 × 1 square. In that case, we are left with the 1 × (m – 1) table, and we know that we can fill the 1 × (m – 1) table in Jm – 1 different ways. If we, instead, start with the 1 × 2 rectangles, we are left with the 1 × (m – 2) table to fill, and we know we can fill that table in Jm – 2 ways. So, when we add this up, we get that Jm = Jm – 1 + Jm – 2. 

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So, the main point here is to know the proportions of materials around the solar system. As you all know, the solar system isn’t the same temperature at all places. Near the start, it is boiling, and far away from it is very cold. So, the state and type of material are based on distance. For this part, we will need a little bit of chemistry. So, the 3 states of matter are:

solid, liquid, and gaseous.

Solid

So, solid matter is when the atoms are stable and closely bound together. The solid matter has a constant mass and volume. Most substances are solid.

Liquid

The liquid matter is when the atoms are stable but loosely bound and change their position based on their container. So, that is why water flows in places where it is put. Liquids have a constant mass but change volume. 

Gaseous

The gaseous matter is when atoms are unstable, very loosely bound, and constantly in motion. That is why gasses are very faint because their densities are small. 

If temperatures are high, the matter is gaseous, and matter tends to solidify if it is freezing. With that conclusion, we can discuss the distribution of materials in the solar system. So, 98% of a solar system is made up of hydrogen and helium, although most of it goes to the star. 1.4% of the materials go to hydrogen compounds found in rocky planets in the habitable zone or gas giants. Rock is responsible for 0.4% of the mass in the solar system. It is found in the cores of the planets and on the surfaces of rocky planets. Finally, metals are responsible for 0.2% of the solar system’s mass, making it the scarcest type of material. It is found in planets’ outer cores, inner cores, and the crust of rocky planets. Here is a graphical representation of all the materials mass distribution in a typical solar system. 

Planets

Small planets

So, planets come in different sizes, but we mainly distinguish between big and small planets. So, let’s start with the small ones. Small planets generally have no atmosphere because their gravity is insufficient to maintain a stable atmosphere. Furthermore, they are tiny, so they are probably not geologically active. Because of their lack of atmosphere has many crater impacts, left to stay imprinted on their surfaces. And finally, being geologically inactive and small, they probably don’t have an outer core. This means that they have no magnetic field protecting the planet from the sun’s radiation. Mercury would fall directly under this category.

Big planets

Big planets have an atmosphere since they can contain an atmosphere. They are also geologically active since they have many inner layers and have a much more heated core. Not that many crater impacts, though; the atmosphere blocks most of them, burning them in the sky. These planets have a magnetic field since they contain a liquid outer core. Finally, they have a leaking atmosphere. Since they contain an atmosphere and aren’t perfectly bound to the planet, gases leak out into space. Earth and Venus fall under this category. Mars is somewhere in between. 

How are planets different based on their position?

Well, distance is significant for a planet’s characteristics. It determines temperature, orbit, and other factors. So what happens at each distance for rocky planets?

Close planets

These planets have no atmosphere since it is too hot to sustain gases in the atmosphere. Also, they are potentially tidally locked, which means they always face the same side towards their star. This can be good or bad for life since on one side it is always dark and on the other always day. So, life would form on the boundary between sun and dark, where temperatures would be normal. Also, there is little erosion. Erosion or weathering is when the weather or time affects the shape of the environment. Since there is no atmosphere, no weather effects can happen, but time does change the landscape, so there is very little erosion. 

Intermediate planets, AKA habitable zone

Here is where the habitable zone lies. Moderate temperatures, liquid water can form, there is a pleasant atmosphere. The distance is perfect for life, especially with liquid water, atmosphere, and average temperatures. 

Far planets

These planets are cold; however, in some circumstances, they can contain life. We will talk about those more later. For now, let’s focus on their characteristics. These planets have ice caps, places where there is frozen water or other frozen substances. Other than that, there is limited erosion due to the cold. There may or may not be an atmosphere pleasant for life. It really depends on the planet. 

Gas giants

Gas giants are a different type of planet. They are huge and composed mainly of gas, as we learned in the previous post. Gas giants have incredibly high pressure due to the immense amount of gas in their atmospheres. This promotes heat and compression, making them super dense. Coming back to its composition, a gas giant contains a lot of ices since it is far away from its star. These ices are frozen water, frozen methane, ammonia, and dry ice (frozen CO2). Due to their size, they also have great gravity, so they have many moons. For example, Jupiter has 79 moons. That is a lot! 

Moons

Moons are a particular class of objects since they orbit planets and form from mini debris disks around young planets. For example, our moon is suspected of forming due to a collision of Earth and planetesimals. However, moons can also be planetesimals that were captured by the gravity of a planet. So far, there has been no exo-moon confirmed, a moon orbiting an exoplanet. Since our telescopes can barely detect exoplanets, how can they see moons! We hope to change that in the future, and try to find exo-moons since they have a great potential for life. 

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Stars, home for planet formation

Stars form in giant molecular clouds, where there is plenty of gas and dust for star formation. However, some events will cause the gravity in the cloud to shift, and a gravitational collapse of material will occur, clumping matter into a ball, a future star. As the matter collapses onto itself, the pressure inside gradually stabilizes with the gravity of its mass, soon reaching an equilibrium. Once the star reaches this equilibrium, we will have a protostar, fusing hydrogen into helium, becoming a true star after a million years. Around this protostar, there is still material left, material perfect for planet formation. 

Accretion | key process of planet formation

Accretion is the main process of planet formation. It is a process by which small objects tick together to make larger objects and is the most common planet formation process. Thus, three different things can form with the word planet in them.

Types of objects from planet formation

• Planetesimals: small objects with a diameter of 10 km, usually found in the asteroid and Kuiper belt
• Protoplanets: intermediate-sized objects, with a diameter of typically 100-1000km
• PLANETS: the planet of the show (see what I did there :), their orbits are clear of materials, making them planets. That is why Pluto is NOT a planet. (Sorry, Pluto)

Frost line

In every solar system in the universe, a line divides the warm and toasty sides from the cold and windy sides of the solar system. This is called the frost line, and inside it are rocky planets, and outside it are icy or gas giant planets. This line is key for another process called differentiation, which separates materials by density, and depends on which materials are found. The materials depend on the frost line, so the composition of planets depends if they are inside or outside the frost line. Let’s see how it’s like for them. 

Rocky planets

These types of planets have a lot of layers, 6 in total. First is the atmosphere, which depends on the planet’s closeness, so there are five layers in total. The first layer of the planet is mostly the crust, where we all live, and the oceans, valleys, and mountains. The next level is the upper mantle, followed by the mantle. Here is where the molten lava is. Finally, er have the outer core and the inner core. The outer core can be liquid or solid, which influences a planet’s magnetic field. The outer core needs to be fluid and the inner core solid for a magnetic field to form, like Earth. 

Gaseous planets

For gaseous planets, it is a different story. They have 4 layers. And the first one is a layer of cold hydrogen; the subsequent layer is a place for supercritical gasses, where they are in a supercritical state. A supercritical state occurs for gas at a specific temperature and pressure. The gas will no longer condense to a liquid regardless of how high the pressure is raised. Filling up the next layer is metallic gases. Finally, we have reached the rocky core or the actual surface of the planet. The core is the same as Earth’s core, but it is the only solid form of matter on the planet. 

That’s it! Next chapter, we’ll focus on planets and moons, how moons form, and their significance for astrobiology. See ya! 

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Janna Levin’s latest book, black hole survival guide, has an ironic title since you cannot survive a black hole. However, her book is a beautifully illustrated guide on everything you need to know about black holes.
She begins the guide with an introduction to herself, about her childhood and growing up loving science. In it, she talks about scientific stereotypes: how scientists aren’t creative and memorize equations. However, that isn’t how science works. It requires a whole bunch of creativity, and it requires you to know some equations too. Science is a place where you explore new ideas and forge new theories to explain the beautiful world around us. It helps us see who we are and how we fit in the universe’s picture. As she stumbled onto the path of a scientist, she realized all these things. She became an amazing scientist today, discovering the secrets of black holes.

Gravity, space and time

In her following chapters, she talks about the constituents of a black hole: gravity, space, and time. In the book, you’ll discover that gravity is not what it seems and that free fall is a weird twist in nature. You’ll also learn that space is a vast place, where matter tells space how to curve, and space tells matter how to move. Meanwhile, time is trickier to comprehend, with its delusions and changes depending on gravity. These things interconnect together like the ingredients of a good soup: without one, it wouldn’t be perfect.

Black holes

After clearing up common misconceptions and altering world views, she discusses black holes, and in turn, nothingness. First, she describes black holes as nothing, which they at their cores are. However, they turn out to be just a little more than nothing. They offer universe-shaking facts and almost ruin all of physics because of one simple value: information.

We have talked about information and black holes before on the blog and channel. In the book, she talks about holography and how the entire universe might be a simulation due to the information paradox. The hologram principle is that the universe might be a simulation if black holes stores information in 2D form on their 3D surfaces. Imagine being a simulation for a second. Everything you ever did, think, thought, or anything humanity or any civilization in the universe has done isn’t real. It is all part of some master beings plan or a videogame their children play.

But, she gives some comfort to the reader: science has come a long way. We will have a way of finding out the truth, and we will solve the information paradox. Just give it time. She was right, with it being partially solved today. You can check out my video or post on how that works.

Endings

Black hole survival guide by Janna Levin was a fantastic small read, being intellectually stimulating and easy to read. Her writing is clear and decisive, with no uncertainty in her knowledge or facts. She shares world-shaking views with a clear and unwavering voice and is very direct with them. I admire this quality. After all, we have to accept direct statements and not soften them because we don’t want to be dramatic. Science is dramatic. And so is nature.

Black hole related things

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