All objects and substances are made of matter. For example, steel is made from iron, mined from deep within the Earth. But how, where and when was the iron first made? Perhaps because of its abundance, we hardly give matter a thought. This article traces the primal origins of all matter and its travel through space and time.
All matter is composed of molecules. These are formed when atoms (aka chemical elements) interact and form bonds with each other. Molecules can be very simple (for instance, water) or large and complex as in the case of DNA.
Atoms themselves cannot be created by chemical reactions. Amazingly enough, to understand atom formation, one must look up at the stars and space. Atoms contain three sub-atomic particles: negatively charged electrons, positively charged protons and uncharged neutrons. Protons and neutrons are at the atom’s centre, the nucleus, while electrons swirl around the nucleus. Each type of atom is characterised by a given number of sub-atomic particles. Hydrogen, with one proton and one electron, is the simplest and most abundant atom in the universe. However, to understand how molecules were formed we need to look at the stars.
The most accepted hypothesis for the origin of the universe is the Big Bang Theory. Soon after the Big Bang, the universe was an extremely hot soup made up of photons, electrons, protons, neutrons and neutrinos. As it cooled, the components joined to form neutral atoms. The universe which, until then, was opaque, grew transparent, and the photons, or light quanta, were able to escape outward. This first light can be seen today and is called the cosmic microwave background. Clumps of matter formed and grew into stars that were held together by the force of gravity.
Crushed together by gravity and with the increasing temperature and pressure, nuclei underwent nuclear fusion. First, four hydrogen nuclei, or protons, fused together to form a nucleus having two protons and two neutrons. The newly formed helium nucleus had a slightly lower mass than the four hydrogen nuclei and the rest was radiated as energy, following Einstein’s relation E=Mc2 which connects energy and mass. This is how the first star and all stars ever since began their lives.
The radiation pushes outward and prevents the star from collapsing due to the inward pull of gravity, thereby stabilising it. Stars can continue like this, depleting hydrogen and building up helium, for billions of years.
When the core runs out of hydrogen, and if a star is sufficiently massive, the gravity will be able to start a second type of fusion reaction. In this, three helium nuclei, having six protons and six neutrons in all, will fuse to form a carbon nucleus having the same number of both particles. The energy emitted in the form of radiation pushes against gravity and and establishes a new equilibrium. This is the second phase of a star’s life, which can last for a few hundred million years.
As the helium depletes, the star will be left with a carbon rich core, surrounded by layers of helium and hydrogen that are too cool to fuse. The effect of gravity on the core initiates a new reaction in which carbon and helium fuse to yield oxygen and energy.
Each step of the reaction ladder creates a heavier atom and a hotter core while the star swells up into a red giant. It now has multiple layers, each occupied by one or more types of nuclei. The ultimate step is the fusion of silicon to iron.
Towards the end
All the reactions that occurred until now caused a net release of energy, allowing the star to equilibrate with gravity. But iron cannot fuse to a larger, stable atom and instead breaks down into many smaller particles. This reaction consumes energy and so cannot provide the stabilising radiation pressure; in the absence of this outward force, the star begins to collapse inwards. From now on, there are different paths that stars of differing masses follow. Low mass stars, after the helium gets fused into carbon, collapse to form brown dwarfs or white dwarfs. In very massive stars, with mass about 10 times that of our sun, pressure builds up to such an extent that it triggers a supernova.
During a supernova, the core collapse triggers a shock wave that expels material from the surrounding layers. This compresses and heats these layers, initiating fusion in them. It also expels vast numbers of sub-atomic particles at close to the speed of light. The two events cause an explosion of unimaginable proportions, sending material far into the interstellar space. Then if the remnant core has a mass that is approximately more than three times the sun, it will shrink to become a black hole.
The expelled atoms will eventually slow down to form a nebula and become a seeding area for new stars. This is how the matter of our solar system, and in fact, the universe itself, was created.
It is fascinating to think that atoms that were once forged deep inside a star and expelled during its death have been co-opted to become my physical body and all the things that I need to live.
ramesh.distill@gmail.com
