The life cycle of star: Stages in the birth and death of a star

Explore how and when the stars are born and how far they live…

The life cycle of a star is determined by its mass. The greater the mass of the star, the shorter is its life span. The hottest stars are blue in color, and the coolest one appears red. The life cycles of the stars are almost same up to main sequence (i.e. – red-giant phase). And after that they have unique way of dying out as per their masses.

The life of a star about one solar mass

Stage 1-

Stars are born in a region of high density Nebula, and condenses into a huge globule of gas and dust and contracts under its own gravity.

Stage 2 -

A region of condensing matter will begin to heat up and start to glow forming Protostars. If a Protostar contains enough matter the central temperature reaches 15 million degrees centigrade.

Stage 3 -

At this temperature, nuclear reactions in which hydrogen fuses to form helium can start.

Stage 4 -

The star begins to release energy, stopping it from contracting even more and causes it to shine. It is now a Main Sequence Star.

Stage 5 -

A star of one solar mass remains in main sequence for about 10 billion years, until all of the hydrogen has fused to form helium.

Stage 6 -

The helium core now starts to contract further and reactions begin to occur in a shell around the core.

Stage 7 -

The core is hot enough for the helium to fuse to form carbon. The outer layers begin to expand, cool and shine less brightly. The expanding star is now called a Red Giant.

Stage 8 -

The helium core runs out, and the outer layers drift of away from the core as a gaseous shell, this gas that surrounds the core is called a Planetary Nebula.

Stage 9 -

The remaining core (that is 80% of the original star) is now in its final stages. The core becomes a White Dwarf the star eventually cools and dims. When it stops shining, the now dead star is called a Black Dwarf.

Massive Stars – The Life of a Star of about 10 Solar Masses

Massive stars have a mass 3x times that of the Sun. Some are 50x that of the Sun.

Stage 1 -

Massive stars evolve in a similar way to a small star until it reaches its main sequence stage (see small stars, stages 1-4). The stars shine steadily until the hydrogen has fused to form helium (it takes billions of years in a small star, but only millions in a massive star).

Stage 2 -

The massive star then becomes a Red Super giant and starts of with a helium core surrounded by a shell of cooling, expanding gas.

Stage 3 -

In the next million years a series of nuclear reactions occur forming different elements in shells around the iron core.

Stage 4 -

The core collapses in less than a second, causing an explosion called a Supernova, in which a shock wave blows of the outer layers of the star. (The actual supernova shines brighter than the entire galaxy for a short time).

Stage 5 -

Sometimes the core survives the explosion. If the surviving core is between 1.5 – 3 solar masses it contracts to become a tiny, very dense Neutron Star. If the core is much greater than 3 solar masses, the core contracts to become a Black Hole.

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