When Star’s Die!

Supernova: The Final Chapter in a Star’s Life

I’ve been casually talking about science since the late 1990s, back when I was in high school. Later, around 2006/07, when I started using the internet personally, I had a few fans and followers on platforms like Yahoo Messenger and Orkut. Although in Bangladesh, the number of people interested in science is very low. In a society where politics, religion, and rote learning are given the highest importance, it’s natural that only a handful – maybe one or two – will be interested in science. Perhaps that’s why Bengalis may have to remain laborers on the global stage for another century. A nation that still believes in ghosts living in banyan trees sees supernovae as the work of spirits, demons, monsters, and mythical beings. Some even try to reconcile science with religion. But science and scientific theories are changeable – today’s theory can be disproven by tomorrow’s. Religious beliefs, on the other hand, are unchanging. So trying to align science with religious views is nothing but childish and uninformed thinking. Anyway, let’s return to supernovae.

Stars are among the most mysterious and powerful objects in our universe. Their birth, life, and death – all follow the deep laws of mathematics and physics. And the most dramatic form of their death is the supernova – a violent explosion that not only ends a star’s life but also opens the door for new stars to be born.

Generally, stars survive through nuclear fusion. The nuclei of hydrogen atoms collide and fuse to form helium, releasing immense energy in the process. This energy gives the star its light, heat, and presence in the universe. Our Sun has been shining in this way for billions of years.

However, this fusion isn’t naturally possible on Earth. It requires temperatures of several million Kelvin and a density of nuclei that Earth’s environment cannot provide. When we touch an object, we don’t actually touch its nucleus – the force from electrons gives us the sensation of touch. But inside stars, the temperature is so high that electrons are stripped away from nuclei, allowing the nuclei to move freely. In this state, they can collide and fuse – making fusion possible.

Humans have mimicked this process in hydrogen bombs, where uncontrolled fusion occurs. But controlled fusion has not yet been successfully achieved. Research is ongoing, because if controlled fusion becomes possible, it will be a revolution in energy – where the output exceeds the input.

The energy produced by nuclear fusion at the core of a star is initially emitted as gamma rays. But in stars like the Sun, the density is so high that these gamma rays cannot escape easily. They lose energy through collisions with electrons, change direction, and gradually transform into lower-energy photons. It can take thousands of years for a single photon to escape from the Sun’s interior.

These photons heat up the electrons through collisions, and this heat creates pressure inside the Sun that counteracts gravity. Without this pressure, the star would collapse, and fusion would stop.

Through fusion, hydrogen turns into helium, then carbon, oxygen, and other elements. Eventually, iron is formed, and fusion stops – because no more energy can be extracted beyond iron. At this point, the balance inside the star breaks – gravity begins to compress it, and fusion pressure can no longer resist. This leads to a supernova – a massive explosion that scatters the star’s materials into space.

This explosion is so intense that particles can travel from one end of Earth to the other in a single second. The scattered material heats up and emits light, making the supernova visible. Initially, it emits visible light, but within days, the explosion expands, cools down, and shifts to infrared light.

However, since supernovae are very far away, we can observe them for months. Most supernovae are several megaparsecs away – one megaparsec is about 3 million light-years. Because of this distance, we observe them through telescopes.

The last supernova visible to the naked eye occurred in 1604, when astronomer Kepler observed and documented an explosion in our own galaxy.

This explosion is not just the death of a star – it spreads new elements across the universe, which can become the foundation for future planets, life, and civilizations. So a supernova is not just destruction – it’s a message of rebirth.