The life of a star is a fascinating journey, governed by its initial mass. Stars are born in dense regions of gas and dust known as nebulae.

Star Formation

All stars begin as protostars within a nebula. Gravity causes the gas and dust to collapse, increasing temperature and pressure at the core. When the core reaches about 15 million degrees Celsius, nuclear fusion of hydrogen into helium begins, and the protostar ignites, becoming a Main Sequence Star.

Low-Mass and Intermediate-Mass Stars (Up to 8 Solar Masses)

Low-mass stars, like our Sun, spend the majority of their existence on the main sequence.

Main Sequence Phase

During this phase, a star is in hydrostatic equilibrium—the outward pressure from fusion balances the inward force of gravity. This stage lasts billions of years.

Red Giant Phase

When the star exhausts the hydrogen fuel in its core, the core contracts, and the outer layers of the star expand dramatically and cool, turning the star into a Red Giant.

Final Stages

After the Red Giant phase, the outer layers drift away, forming a Planetary Nebula. The remaining hot, dense core is a White Dwarf, which slowly cools over billions of years to become a Black Dwarf.

High-Mass Stars (Over 8 Solar Masses)

Stars with a mass greater than eight times that of the Sun have a much shorter, more dramatic life.

Main Sequence and Supergiant Phase

High-mass stars burn through their fuel much faster than low-mass stars. After the main sequence, they expand into a Red Supergiant. They continue fusing heavier elements in their core, moving past helium to carbon, neon, oxygen, and silicon, until the core is mostly iron.

Supernova

Since iron fusion consumes energy rather than releasing it, the core collapses in a fraction of a second. This collapse results in a massive explosion known as a Supernova.

Remnants

The remnants of a supernova depend on the star's initial mass:

• Neutron Star: If the remaining core mass is between 1.4 and 3 solar masses, it collapses into an incredibly dense Neutron Star.
• Black Hole: If the remaining core mass is greater than 3 solar masses, gravity overcomes all other forces, and the core collapses to an infinitely dense point, forming a Black Hole.

Summary of Stellar Evolution Paths

Here is a simplified view of the different stellar evolution paths based on initial mass.