Stars are born from contracting nebulae of gas and dust. They spend most of their lives on the main sequence, fusing hydrogen into helium in their cores. Eventually they run out of fuel in their cores and their outer layers expand, forming red giants or supergiants. From there, smaller stars shed their outer layers to form planetary nebulae and white dwarfs, while larger stars explode as supernovae, leaving behind neutron stars or black holes.

1. Life Cycle of a Star

3. Birth
• Stars are born in the nebula, which are huge
clouds of gas and dust. The nebula begins to
contract under the pull of its own gravity. This
forms a protostar.

4. Protostar
The star begins to take shape. The
temperature continues to rise and nuclear
fusion begins to take place. The pressure from
inside the star finally equalizes the gravity
pushing in, and the star stops contracting.

5. Nebula
Sun size stars
Huge Stars
Giant Stars

6. Main Sequence Star
• Stars live out the majority of their lives in a
phase termed as the Main Sequence. This is
the longest, most stable period of a star’s life.
It converts hydrogen to helium in its core,
generating heat and light.

7. Red Giants and Supergiants
• As the nuclear fuel becomes depleted the core
contracts and our layers expand.

8. Sun Size Star
Sun  Red Giants  Planetary Nebula 
White Dwarf  Black Dwarf 

9. Planetary Nebula
• Now the outer layers of the star start to drift
off into space. The star loses most of its mass
to the nebula.

10. White Dwarf
• The star cools and shrinks. No nuclear
reactions take place and the faint star radiates
it heat into space.

11. Black Dwarf
• The star will eventually lose all its heat and
energy and become dark and cold.

12. Huge Stars
Huge Star  Red Supergiant  Supernova  Neutron star

13. Supernova
• The core collapses in an instant. Forces in the
core overcome the gravitational forces,
causing a massive, short-lived explosion.

14. Neutron Star
• It contracts into a small star that has
extraordinarily strong magnetic field, and a
rapid spin.

15. Giant Stars
Giant Star  Red Supergiant  Supernova  Black Hole

16. Black Hole
• It contracts and becomes a black hole. The
gravitational field is so strong that even light
cannot escape.

17. H-R Diagram
• The Hertzsprung-Russell Diagram is a graphical
tool that astronomers use to classify stars
according to their luminosity, spectral type,
color, temperature and evolutionary stage.