Stars and Atoms

Our journey will almost be over before the human race arrives at a reasonably accurate answer to the question of how old the sun is and where it gets its energy from. As stars are pretty much the most important things out here in space, it makes sense to explain how stars really work now rather than wait for humanity to work it out over the next few thousand years. The source of energy that makes the sun shine and the stars shine is a continuous nuclear bomb, an H-bomb or Hydrogen bomb. The surface of a star like the sun is around 6,000 ^oC but the core is nearer 15 million ^oC which for those of you more familiar with gas ovens is about gas mark 79,000.

"So long can this H-bomb burn for?"

Stars, in fact the whole universe, are made up of mostly of this material called hydrogen, and stars are huge so they can shine for billions of years. The sun has been shining for 4.5 billion years and can keep going for another 4 billion years. This energy comes from the process of nuclear fusion, where atoms are combined to create completely different atoms and in the process release colossal amounts of energy.

"I’m not sure I really understand what an atom is"

An atom? Atoms are what everything is made from. They are the building blocks of the universe, sort of like LEGO. Atoms, like LEGO, come in different shapes but atoms are really minute, so small you can't see them even with a microscope. This atom idea dates back almost to the start of our journey. Democritus of Abdera was an ancient Greek philosopher from around 400 BC and developed the first well thought out concept of the universe being made up of atoms. As a young man he travelled to Athens to meet Anaxagoras, the hot rock man, but was very upset when Anaxagoras refused to meet him. Democritus has the consolation that his own ideas have lasted far longer than the famous older philosopher who snubbed him. At one time everyone thought that atoms were unchangeable. You could break things down into the individual atoms but they thought that you couldn't turn one atom into another or break up an atom. There aren’t even that many types of atoms, only 92 different types exist naturally.

"You're trying to tell me that everything is made up from just 92 types of atoms?"

I am indeed and each of these different types of atom is called an element. They vary from the very smallest which is hydrogen to the biggest which is uranium. Even more surprising is that despite all these different types of atoms or elements, nearly three quarters of the whole universe is made up of hydrogen atoms. So most of the universe is made out of a single type of atomic LEGO brick.

There's a diagram called the Periodic Table, first developed by the Russian Dmitri Ivanovich Mendeleev in 1869 that lists out all the atoms/elements in terms of size. Hydrogen is the smallest, followed by helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, neon…

“OK, I believe you. I don’t think I’ll be able to remember all 92 anyway.”

Well like I always say, imagination is more important than knowledge. As long as you can imagine a universe made from 92 different elements that is more important than remembering all their names. That’s what reference books are for, to hold all the boring facts you can’t remember or don’t really need to remember.

You don’t even need lots of different types of atoms to make complicated things. Human bodies are amongst the most complicated things in the universe, but incredibly humans and most living things are basically made up of just six elements; carbon, nitrogen, oxygen, hydrogen, calcium and phosphorus. These six types make up 99% of your atoms with the last 1% a range of other rarer atoms.

"That's not many types of building blocks; LEGO would be dull with only six types of blocks"Well when you start combining atoms or LEGO blocks there’s an almost infinite range of things that can be built. Take just six LEGO blocks of the same size with 2 by 4 little studs, all the same shape and colour, and you could make 102,981,500 different shapes. How fast could you click together 6 LEGO blocks?“Oh, two or three seconds I suppose.”

Well at that speed it would take you almost ten years to try all possible ways of clicking together just six LEGO blocks. So it’s no wonder that you can build an entire universe out of 92 different types of atoms.

“It must take a while to make a universe then?”

Oh, it does. This one is almost fourteen billion years old after all. .

"So is light made of atoms?"

No, although all physical things in the universe from stars to humans are made from atoms we’re not. We photons are different; we're a form of energy and exist just as we are. Like heat, we can affect atoms but aren't made of atoms. Take a fire. The smoke coming out of a fire contains atoms but the light and heat you feel from a fire is energy and, in fact, is a type of photon like us. But let’s finish off atoms first. Atoms were initially thought to be the smallest division of matter but, in fact, atoms themselves are made of particles. An atom is made up of a nucleus which defines what sort of atom it is and a cloud of particles called electrons that spin around the nucleus. The electrons have a negative electrical charge and are the particles that help to carry an electrical current through a wire. The electrons are also the parts of atoms that can link atoms together to make different combinations of atoms that are called molecules. Your body is held together by these interactions of electrons which are called, reasonably enough, chemical bonds.

"Hold on Albert, let me get this staight. Atoms join together to make molecules."

That's right.

"Are humans just big molecules then?"

Well humans are made up of thousands of different types of molecules and each of those molecules is made up of atoms. By combining different atoms in different shapes the same six atoms (with a few extras thrown in here or there) can make up all the important molecules in a human like DNA and proteins. Have you heard of DNA?

"Like in Jurassic park?"

Fascinating thought recreating dinosaurs. I just read about it while I was waiting for you to join me. I'll explain all that a bit later but let's sort out the basics first. Now, where was I? Oh, yes, the glue between atoms is made up of electrons which make up chemical bonds. These bonds are where two atoms both think an electron belongs to them and hold onto them tightly.

"So if both atoms are holding onto the same electrons then the two atoms stick together, like a pair of kids 'sharing' the same toy."

Well sort of, but it does get a little more complicated from here. There are a few more names to remember about how atoms are put together, but it's worth the effort because you need these facts to know how stars shine. The nucleus is made up of two types of particles called protons and neutrons. The number of protons in a nucleus defines what element it is and neutrons somehow help to hold everything together. Remember the periodic table I just told you about?

"Hydrogen, helium, lithium and all that?"

Precisely. Well one proton means that atom is hydrogen, two protons means helium, three makes lithium and so on.

"And it doesn't matter how many electrons or neutrons, two protons in an atom is always helium?"

That's right. The protons determine the essence of what an atom is. The neutrons and electrons are important but not as critical. Take a dog. If it looses a leg and some of its fur it's still a dog inside and will still look like a dog even if it is three legged and a bit mangy looking. Legs and fur are like neutrons and electrons, important pieces of whole picture but the essential doginess is set by the protons.

As well as defining the type of atom, protons also carry a positive charge that helps to hold the fast moving electrons in their orbits. Remember the electrons have a negative charge and like the opposite ends of two magnets, positive and negative attract each other. So protons help the atom to hold onto its electrons. The simplest element hydrogen has a nucleus of one proton and one electron whizzing around it. Oxygen has eight protons, usually eight neutrons and usually eight electrons. A really heavy atom like Uranium-238 has 92 protons and 146 neutrons. Still with me?

"I think so."

There are a few more names worth hearing about, mainly because the names are so weird. You'll also impress people if you know this last piece of the atomic jigsaw puzzle. Even protons, neutrons and electrons are not the end of the story. They are made up of smaller particles called quarks. Scientists have made up some curious names for these quarks like ‘up’, ‘down, ‘strange’, ‘charmed’, ‘truth’ and ‘beauty’. In an attempt to be taken more seriously some scientists have renamed truth and beauty to top and bottom, but I rather like the original names. A proton contains two up quarks and a down quark whereas a neutron has one up and two down quarks. Naturally they are all held together with particles called gluons.

"You're making this up as you go along."

No Honestly that's what they are called. But don't worry about quarks, unless you just like the names, we can still explain most of the universe without thinking about quarks. All the same it's nice to know that everyone of you has inner beauty, truth and charm no matter how well it's hidden at times.