The Life Cycle of a Star (in detail)

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  • Created by: petrblak
  • Created on: 06-02-16 09:41

Stage 1 - Nebula

A nebula is formed when dust, hydrogen, helium and plasma clump together as a result of gravitational pull.

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Stage 2 - Protostar

The nebula gathers even more materials and its increasing gravity compresses it, making itdenser and hotter. This is called a protostar.

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Stage 3 - The Birth of the Star

Gravitational energy is converted into heat energy so the temperature rises. When the temperature is high enough, nuclear fusion is able to occur where hydrogen nuclei form helium nuclei, giving out massive amounts of heat and light. A star is born.

Smaller masses around the star also pull together to form planets which orbit the star.

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Stage 4 - Main Sequence Star

The star immediately enters a long, stable period where outward pressure caused by nuclear fusion is balanced by gravity. The star remains in this period for millions of years due to the massive amounts of hydrogen there is to use up (or fuse). This is called a main sequence star.

Our Sun is in the middle of this stage.

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Stage 5 - Red Giant OR Red Super Giant

Eventually, after billions of years, the hydrogen in the star begins to run out. Some nuclear fusion of helium occurs, forming heavier elements such as iron. The star then swells as a result of the inbalance of outward pressure and gravity and the surface of the star become red.

If the star is large, it will form a Red Super Giant, but if it is small or medium sized (like our Sun) it will form just a Red Giant.

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Stage 6 - Supernova OR White / Black Dwarf

A Red Giant then becomes unstable and ejects (or sheds) its outer layer of dust and gas as a planetary nebula. This then leaves a hot dense, solid core known as a white dwarf. The white dwarf then cools to become a black dwarf which eventually disappears.


A Red SUPER Giant, however, starts to glow brightly, undergoing more nuclear fusion, expanding and contracting and forming elements no heavier than iron. The red super giant then , forming elements much heavier than iron and ejecting them into the universe to form new planets or stars.

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Stage 7 - Neutron Star OR Black Hole

Left behind from the supernova is a very dense core called a neutron star. If this star is big enough it will become a black hole.

Only Red Super Giants can form neutron stars or black holes.

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