EVOLUTION OF THE SUN 

The evolution of the Sun is a journey spanning billions of years, from a collapsing cloud of gas to its eventual end as a fading stellar remnant.

Here is the life cycle of the Sun, broken down by stages:

1. Giant Molecular Cloud (The Beginning)

The Sun began approximately 4.6 billion years ago within a massive, cold cloud of hydrogen gas and cosmic dust.

A nearby disturbance (possibly a supernova) caused the cloud to collapse under its own gravity.

As it collapsed, it began to spin and flatten into a disk, with most of the mass concentrating at the center.

2. Protostar Phase

The central core grew increasingly hot and dense.

During this stage, the Sun was not yet a "star" because nuclear fusion had not started.

It glowed due to the kinetic energy of the collapsing material turning into heat.

3. Main Sequence (Current Stage)

Once the core temperature reached about 15 million°C, nuclear fusion ignited. Hydrogen atoms began fusing into helium, releasing massive amounts of energy.

Hydrostatic Equilibrium: The Sun is currently in this stable phase, where the outward pressure of fusion perfectly balances the inward pull of gravity.

The Sun will spend a total of about 10 billion years in this stage; it is currently middle-aged (4.6 billion years old).

4. Red Giant Phase (In ~5 Billion Years)

When the hydrogen in the core runs out, the core will collapse, causing the outer layers to expand significantly.

The Sun will grow so large that it will likely swallow Mercury, Venus, and possibly Earth.

While the surface will be cooler (appearing red), the core will become hot enough to begin fusing helium into carbon.

5. Planetary Nebula

Once the helium is exhausted, the Sun’s outer layers will become unstable and be ejected into space.

This creates a glowing shell of ionized gas known as a planetary nebula, which will disperse heavy elements back into the universe to form new stars and planets.

6. White Dwarf (The End)

The remaining core—about the size of Earth but incredibly dense—is left behind.

Fusion has completely stopped. The Sun is now a White Dwarf, glowing only from leftover heat.

Over trillions of years, it will eventually cool down completely to become a cold, dark Black Dwarf.