* Fusion slows down: As the star runs out of fuel (hydrogen primarily), fusion reactions decrease. This weakens the outward pressure that balances gravity.
* Gravity takes over: With reduced outward pressure, the star's core starts to shrink under its own gravity. This compression increases the core's temperature and density.
* Possible scenarios: The fate of the star depends on its initial mass:
* Low-mass stars (like our sun): The core becomes hot enough to ignite helium fusion, creating a red giant. Eventually, they shed their outer layers, leaving behind a white dwarf.
* Medium-mass stars: These stars experience a more dramatic collapse, leading to a supernova explosion. The core becomes a neutron star, or potentially a black hole if it's massive enough.
* High-mass stars: Similar to medium-mass stars, they also experience a supernova explosion, leaving behind a neutron star or a black hole.
In essence, the imbalance between fusion and gravity causes the star to contract, leading to a series of dramatic events that determine its ultimate fate.
