Life cycle of the starts

A star is formed from a nebula, which is a huge cloud of interstellar dust and a mixture of gases, primarily hydrogen.
Nebula Characteristics:
- Composed mostly of hydrogen, the most abundant element in the universe.
- The mass of the dust and gases causes the nebula to contract under its own gravity.

As gravity pulls the dust and gas particles together, it leads to the formation of clusters within the nebula.
This clustering causes significant particle interactions, resulting in:
- Particles gaining kinetic energy.
- Collisions among particles that elevate temperatures.
The temperature in the nebula clusters can rise to millions of degrees Celsius, resulting in the formation of a protostar, which is essentially an infant star.

Nuclear Fusion Process:
- Begins in the core of the protostar when reaching temperatures around 15 million degrees Celsius.
- Fusion reactions convert hydrogen into helium, releasing energy.
The energy produced generates heat and light, leading to the star entering its main sequence phase.

Over several billion years, low-mass stars, similar to the Sun, consume most of the hydrogen in their cores, causing the cessation of hydrogen fusion.
Hydrogen is still present in the stars' outer layers, allowing fusion to occur there, which leads to:
- Increased temperature causing the star to heat up and significantly expand.
- Formation of a red giant as the outer layers expand.
As the red giant cools, gravity takes precedence, led to the core collapsing into a white dwarf.
- Eventually, the white dwarf cools down completely, becoming a black dwarf—an object that emits no light.

Massive stars expand into red supergiants, noted as the largest type of star known.
These stars have a quicker burning rate of hydrogen fuel, leading to a rapid collapse once fuel is depleted.
The rapid collapse invites high temperatures and pressures, resulting in:
- A supernova, which is a violent explosion of the star’s outer layers.

Following a supernova explosion, the dense core left behind can evolve into different celestial objects based on its mass:
- Smaller Masses: Form a dense core predominantly composed of neutrons, known as a neutron star.
- Larger Masses: Collapse under gravity into an extremely small point of infinite density called a black hole.
The gravitational pull of a black hole is so potent that not even light can escape from it.

Videos:
- "Immortal Suns: How Dark Matter Could Make Stars Live Forever" (8 mins)
- "Life Cycle of Stars" (5 mins)