1. Life Cycle of Stars

2. • Every star has a life cycle: a
beginning, a middle and an end.
At the beginning, a star forms
from a massive cloud of gases
and dust called a nebula (gases
include hydrogen and helium).

3. • The gravitational forces begin to pull the
gas and dust particles close together,
creating clumps. The clumps become
more massive and gravity becomes even
stronger. Over time, a dense region
forms, called the protostar.

4. • Gravity causes the core of the protostar
to become very tightly packed and the
pressure causes nuclear fusion to begin.
Hydrogen atoms in the core fuse to make
helium atoms and as a consequence,
produce tremendous amounts of energy.
• Billions of years after forming, the star
begins to burn out.

6. Stars like the Sun
• For about 10 billion years, a star’s available
hydrogen will have been converted to
helium. With less hydrogen to burn, the
core begins to contract and gets hotter,
while the outer layers of the star expand and
then cool. The star evolves into a red giant.
Our sun will become a red giant in 5 billion
years. The outer layers of the star drift off
and leave a small, dim hot core behind – a
white dwarf.

9. More massive stars
• Stars that are more massive than our Sun
(i.e. 10 times more larger) will become a
red supergiant. Once fusion stops, the
supergiant will have its contents collapse
on its self under its own gravity. The outer
layers of the star explode outwards –
known as a supernova.

11. Supernova
• All the atoms we are
made from came
originally from these
giant supernova
explosions.

12. If a star’s initial mass was:
• between 10 and 30 solar masses  a
neutron star is formed – an extremely
dense star composed of tightly packed
neutrons.
• greater than 30 solar masses  black
hole is formed – a quantity of matter so
dense and gravity so strong that not even
light can escape.

14. Life Cycle of Stars