Stars are the cosmic engines that drive the evolution of galaxies, containing the majority of the visible matter in the universe. However, like many other things in the universe, stars live mortal. But how can stars ‘die’ if they are nothing but a massive sphere of hydrogen and helium? To understand, it is crucial to grasp the process that fuels these gigantic celestial bodies, nuclear fusion. In all stars, the force of gravity pulls all matter towards its center.

This immense pressure and heat at the core of stars enable nuclear fusion where lighter elements merge to form heavier elements, releasing vast amounts of energy. This radiation and heat create an outward pressure that balances the inward pull of gravity, maintaining the star's stability over millions to billions of years.

SN 1054 remnant (Crab Nebula), NASA

Nevertheless, this balance is not eternal. Eventually, the star’s core begins to fuse iron. Iron has one of the highest binding energies per nucleon, requiring energy to undergo fusion or fission. This results in iron accumulating in the star's core, resulting in its collapse. The star’s fate depends on its mass, deciding whether the star will become a white dwarf, a neutron star, or a black hole. White dwarfs form from the remnants of low to medium-mass stars, including the Sun. White dwarfs can prevent collapse due to electron degeneracy pressure.

As fermions, electrons in a system cannot occupy the same quantum state simultaneously. As the star is compressed to extreme densities, the electrons in the atoms are forced into fixed volumes, which means its momentum must increase (Heisenberg’s Uncertainty Principle). Yet, even electron degeneracy has its limits: the speed of light. At the Chandrasekhar limit of 1.4 solar masses, the sheer density causes the protons to capture the electrons, forming neutrons and releasing neutrinos. The neutrinos cause a massive explosion, otherwise known as a supernova. Because neutrons are approximately 1800 times heavier than electrons, their degeneracy pressure is much stronger than electrons.

In even heavier stars, not even neutron degeneracy pressure can save them from total collapse, which results in the formation of a black hole. In conclusion, the life and death of stars, driven by the delicate balance of gravitational collapse and nuclear fusion, serve as profound cosmic phenomena that not only shape the universe's landscape but also offer invaluable insights into the fundamental forces governing celestial bodies.

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