The life cycle of stars
Stars are massive fireballs that glitter throughout the universe in different shapes and sizes. It is very uncommon to come across similar stars as they can range from 450x smaller to over 1000x larger than our sun. A star's mass is measured in the unit solar mass with I solar mass being the mass of our sun. Stars can range from a twelfth of a solar mass to over 50 solar masses. The colours of stars are determined by their temperature with blue being the hottest to red being the coolest. Size has a similar correlation to temperature as the bigger the star is the cooler it gets. The energy that provides these temperatures are from nuclear fusion contained in the core of the star. This brightness is measured in magnitude, the brighter the star the less magnitude it has.
The origin of the stars
Stars are born in regions with high densities of gas called Nebula. When there is enough gas to form a gravitational attraction the gas contracts under its own gravity.
This region of condensing gas will begin to violently heat and start glowing to form a Protostar. At this stage, the protostars gravity is stronger than the repelling forces acting against it which will cause the gas to start reacting and fusing. The temperatures can get to around 15 millions degrees celsius and this is enough heat for the nuclear fusion to being within the star.
When the fusion between the hydrogen and helium begins huge amounts of energy are released. This energy repels the gravitational attraction until a state of equilibrium is achieved, this is when both forces are equal so no movement occurs. When this state of equilibrium is achieved, depending on the mass of the star, it will stay in the state for billions of years. Stars with a larger mass are bigger than other stars so their gravitational attraction is stronger, therefore to keep the equilibrium the hydrogen and helium are consumed faster.
These reactions allow heavier elements to be made in the core, this includes beryllium, lithium, boron etc. up to iron in the periodic table. Only smaller stars with a higher temperature and longer lifespan make it up to iron. These elements cause fusion to slow down and makes the temperature of the star drop and the outer layers to float away causing the star to appear larger also known as a red giant. When all the helium runs out the smaller star's outer layers completely drift away from the core and the core a white dwarf.
Bigger stars do mostly the same as what I have mentioned above, however there death is quicker and more spontaneous. The large mass in the core means that when the fusion stops the gravity contracts the star again. this takes less than a second and the resulting implosion is called a supernova. A supernova is a shock wave of the imploding core that sends all the outer layers away causing a spectacular image to occur in the universe. If the core of the star survived the explosion it will contract further to become a neutron star. A neutron star is mainly a star of neutrons, with some protons, and it is one of the densest objects in the universe. However, the alternative state of the core is even denser as it becomes a black hole. A black hole is said to have infinite density. The gravitational field is so strong that even light can't escape its attraction and so we can barely detect them giving the name black hole.
The next page will be on black holes so you can learn about them in more detail.
Currently there are 4 fundamental forces that we know of in the universe. Gravity, electromagnetism, the weak nuclear force and the strong nuclear force. These forces combine everything in the universe and without one of these forces all existing matter would rapidly change. If you would like to know about spins and colors that will come up in the articles check out my previous page.
The strong force
The strong nuclear force is the force that holds the nuclei of atoms together against the enormous force of repulsion from the protons. However, the strong force only stays strong at very short distances and the further out two particles go the weaker the force gets. The actual fundamental particle that is said to hold the quarks together in this force is called the gluon. The gluon is a massless particle that carries no normal charge. These gluons are said to be a product of the residual color force of the coloured quarks. Gluons are sort of like rubber bands that loop around the different quarks and keep them all together. The strong force is 1000000000000000000000000000000000000000 (10 with 38 zeros after it) x stronger than gravity.
The weak force is responsible for the decay of nuclei. In a proton there are two up quarks and one down quarks. When an up quark flips to become a down quark the whole composition of the particle changes and it becomes a neutron and vice versa. This is caused by the weak force. So, a true definition of this force is it changes the flavour of the quarks. However, up and down quarks have different electron-volts of energy so if one switches the leftover energy has to be transferred into something. The is the physics of conservation. So when a quark flips the left over electron-volt energy get converted into an electron and an electron neutrino. In radioactive decay, when an atom stabilises it releases beta particles while converting a neutron to a proton. This beta particle is a fast moving electron and is the most basic observation of the weak force at work. The weak force particles are W and Z bosons that have a large mass, therefore making them slow and weak. Like the strong force, the weak force gets weaker the further away the particles are so it can only work on very small distances. The weak force is 100000000000000000000000000 (10 with 25 zeros) x stronger than gravity.
The electromagnetic force acts on anything with an electric charge. This force creates the properties for electrostatic charges, opposites attract and like repel. An example of electromagnetism on the atomic scale is the atom. The electrons (negative charge) orbiting the nucleus that has positively charged protons attract therefore keeping the electrons from flying off into space. The electromagnetic force seems to not get weaker the further apart the acting objects are so, like gravity, it could have infinite size. The particle that is used with the electromagnetic force is the photon aka. light. They have no mass and no charge and can exchange infinitely as just discussed. The main theory of electromagnetism is quantum electrodynamics. The electromagnetic force is 10000000000000000000000000000000000000 ( 10 with 36 zeros after it) x stronger than gravity.
Gravity is the weakest force out of the ones that I listed above, yet it acts over the longest distances? Unlike the weak and strong forces, gravity has infinite distance at which it can act. A real life example of how weak gravity is is something you can do right now. Firstly, if you jump you have beaten the attraction of gravity for a few seconds, however, if you tried to pick a proton out of your hand it wouldn't go so well, even if you have a high-powered microscope and a scalpel. This is because gravity is the only force that gets stronger with a greater amount of binding agent in this case mass. As gravity is stronger with the more mass you add, we humans don't account for 1% of the mass of the earth so we have a weak gravitational attraction. Therefore when we jump, the earth doesn't attract towards us as much as we attract towards it. So we can break the gravitational attraction by using enough energy to break it for a few seconds. The more energy you have the easier it is to break gravity. However, because of human limitations rockets can only carry so much, so most of the ship is fuel to get enough energy to break the atmosphere. Gravity is supposedly maintained by the graviton particles but none have been detected in experiments so it is still yet to say what is behind gravity.
So gravity is infinite then why isn't the electromagnetic force keeping us in orbit around the sun?
As I explain earlier, the more mass you add the stronger the force becomes but with the electro-mag force the more positive and negative charges you add the more they will attract and eventually cancel out to produce no charge. So that is why gravity dominates the planets because there is more mass in the universe than charge.
One of the biggest goals in physics is to answer the seemingly simple question 'What is the universe made of?'. For the last few centuries, we have found a better and better answer to this question but there is still lots of work to be done. For example, if a human is made of molecules and those molecules are made of atoms then what are atoms made of. Up until the middle of the 20th century this is what we thought the world consisted of, atoms. However, if atoms are the smallest things then what are they made of? Well, this is why you are reading about elementary particles is it not?! I will explain how elementary particles build the structure matter and how these particles are formed because the smart ones in the room are already asking about what elementary particles are made of if they are the smallest thing.
Spins, Colours and Flavours
Before I start talking about the particles and their properties I need to update first-time particles physicists on what some key terms mean when I get to them later on. The key characteristics that create the different groups of elementary particles are their spin, colour, mass, charge and flavours. Currently, there are 17 different elementary particles. The four fundamental forces, the quarks, the leptons and the Higgs boson.
There are 6 types of quarks which are the up, down, charm, strange, top and bottom quarks. 6 types of leptons including the electron, muon and tau leptons with a neutrino counterpart. The quarks and leptons make up a bigger group called the fermions. The 4 fundamental forces are gravity, strong nuclear force, weak nuclear force and the electromagnetic force. Also the Higgs boson.
The mass of these particles is measured in eV (electron-volts). The mass is so minute that 1 GeV(Giga-electron-volt) is equal to 0.00000000000000000000000178 grams and they are so small that light waves are actually bigger than them so we can't see elementary particles with light.
Each variety of elementary particle is given the term ' a flavour', this is just the name that the groups of particles were given to distinguish themselves. Each 'flavour' of elementary particle comes in three different colours, red, green, and blue. These 'colours' are more labels than literal meaning but refer to a unique difference in the same type of particle. These colours must cancel each other out to create white in a compound particle like a proton of otherwise they will not be able to join because of Pauli's exclusion principle or would rapidly decay. Pauli's exclusion principle concludes that no two fermions can have the same quantum mass, so in a proton, for example, one cannot have two red up quarks because they have the same quantum characteristics.
A particle's spin is like a planet spinning on an axis. However, quantum physics tells us that these particles do not have well-defined axises, but for the purpose of simplicity, they do in this scenario. The spin of a particle can tell us how a particle appears at different angles. Spin 0, for example, is like a perfect sphere, where no side is different from another. Spin 1, is like an arrow head, all the sides are different unless you rotate the arrow 360 degrees, a complete revolution, will it look the same. One of the most interesting pieces of the spin theory is the matter particles or fermions. These particles have a spin of 1/2 which means that it takes two full rotations to get the same side again. However, because particles are so small we don't actually know if they are spinning and so this 'spin' is less of a rotation and more like a path of velocity (movement with direction). This is important in the state of atoms because Pauli's exclusion theory also states that no two particles with the same velocity/spin and mass can exist at the same time.
Atoms make up every object you see, this includes your computer, bed, food, it's all just atoms! But to get a deeper understanding of the universe scientists had to uncover what made atoms, atoms! Now we have 12 fundamental matter particles that make up matter, these are called the fermions and consist of the six quarks and the six leptons. One key rule of fermions is that they can never exist on their own they always have to have another quark or antiquark. From Pauli's exclusion theory we now know that no two fermions that have the same quantum mass can coincide wit each other in a compound particle like a proton and that gives fermions different characteristics to determine if they can be in the same quantum state. Quarks can come in three different colours, for example,an individual particle has three different colours, all this information can now give us the building blocks of how atoms are made. In the nucleus of an atom there are protons and neutrons, and in orbit around the nucleus is the electrons. Now let's see how these compound particles are formed. A proton and a neutron have a formation of 3 quarks. The proton has a charge of +1 so now from all the information we have gathered we know that the charges of all the quarks have to equal 1 and they all have to be different variations. Protons are one of the smallest makeup of quarks so they can't be in the GeV in size so that excludes charm, strange, top and bottom, so they must be made of up and down. So from the chart we can see that the up quark has a charge of +2/3 and the down quark has a charge of -1/3. This means that two down quarks and one up quark will create a charge of zero of a neutral charge, creating a neutron. So a proton must be made up of two up quarks and one down quark. Also because the colours have to combine to create white one quark is green, one blue and one red. This is just a simple example of one set of the quarks. The electrons on the outside, however, are just an electron in the lepton group of the elementary particles but, if you know about electron shells, every atom apart from hydrogen has more than one electron. Electrons still have to follow the Pauli exclusion theory and so no two electrons on the shells of atoms are the same.Contact me if you would like me to add more detailed examples using other fermions.
Going back to the point I made about quarks always forming with another. The antiparticle is usually the one that appears in the formation. The antiparticle is basically the same as the normal particle but has the opposite electric or magnetic properties. For example, the antiparticle of an electron is a positron because it has the same mass as the electron but the opposite charge making it positive. The reason for why there is little antimatter left in the world is still very debatable but in the grand scheme of things even if antiparticles were the majority we would call them particles because we wouldn't know different as they are the opposite but have no different effects. So in theory, an electron could actually be the antiparticle to the positron but we would have no idea.
So if elementary particles are the smallest unit of matter then what are they made of?
Well, this is a really tough question to answer because it hasn't even been 100 years since we realised that atoms weren't the smallest things. This brings up the question that there might be particles making up the elementary particles. However, to test this has become harder and harder because we can barely see protons and neutrons and we can't see elementary particles so anything below an elementary particle will be hard to calculate. Most scientists believe we have almost found the end though. Electrons and other elementary particles have fields in which they are created. These fields are similar to that of space-time and could be motivated to create particles by disturbances of energy. However, it will be hard to tell at this current state in time but it definitely isn't impossible, only time will tell.