1. Life Cycles of Stars Where we’re going today…
Learning about where Stars come from and where they go
By the end of this class, you should be able to…
Name the process and fuel used by stars.
Describe the life cycle of a low mass star.
Describe the life cycle of a intermediate mass star.
Describe the life cycle of a high mass star.
What is a black hole?

2. Life Cycles of Stars Stars
A star is an object in space made up of hot gases, with a core that is like a thermonuclear reactor.
The astronomer Carl Sagan once said…
“there are more stars in the universe
than grains of sand on all the beaches of Earth.”
In between stars there is interstellar matter, which is made up of gas (mostly Hydrogen) and dust.
Birth of a Star
Gravity attracts chunks of gas and dust in a nebula to come together

3. Life Cycles of Stars
Over time, gravity causes the mass to grow and eventually the material collapses in on itself and contracts forming a “protostar”
If the mass stays the same, the protostar may shrink and never reach full star status.

4. Life Cycles of Stars
If it collects enough mass (dust and gas), then the protostars core reaches °C and its atoms in the core start to fuse together to form larger single atoms.
Nuclear Fusion – Hydrogen (H) atoms combine to form Helium (He)
At this point the star starts to glow and leftover gas and dust disperse
Energy radiates from the core in every direction as electromagnetic waves
This is how our SUN keeps the Earth warm.

5. Life Cycles of Stars Evolution of a Star
The life cycle of all stars start in nebula’s, but differ depending on the mass of the newborn star…
Low Mass Stars
Small, dim and cool red dwarfs (stays like this for most of their life)
These burn their H fuel very slowly and may last for as long as 100 billion years

6. Life Cycles of Stars
Eventually a red dwarf changes into a very hot, but small, dim white dwarf and quietly burns out

7. Life Cycles of Stars Intermediate Mass Stars
Similar to our sun (stays like this for most of their life)
These burn H fuel faster than low mass stars and last only about 10 billion years
Eventually, an intermediate mass star expands into a red giant and sheds much of its material into space
It then collapses in on itself and slowly shrinks into a small, dim white dwarf
As it cools more, it turns into a black dwarf, a dense, dark body made up mostly of carbon and oxygen

8. Life Cycles of Stars

9. Life Cycles of Stars High Mass Stars
12 or more times the mass of the Sun
These stars consume their fuel faster and become red giants (they last for only 7 billion years)
When their fuel is used up, these massive stars become supergiants
Before long, they collapse in on themselves causing a massive explosion called a supernova
This is important as it spreads heavy elements out through space.

11. Life Cycles of Stars
If the star began with a mass about 12 to 15 times that of the Sun, the remaining core eventually collapses and forms a neutron star.
Neutron stars can start out as
large as 1 million km wide but
collapse into a sphere only
10 km wide.
The core of a neutron star is
°C and may
take trillions of years to cool.

12. If a star is more than 25 times as massive as the Sun, the star collapses into itself and becomes a black hole…

13. Life Cycles of Stars Black holes
Black holes are extremely dense and so they have an extraordinary amount of gravitational pull.
This pull is so strong that not even light can escape their powerful gravitational force
How do astronomers know that black holes exist?
• Material pulled toward the black hole emits electromagnetic radiation that can be measured
• The intense gravity of black holes has observable effects on passing stars and galaxies

14. Life Cycles of Stars
• Results from computer models show how super-dense objects distort light from distant stars (and these match observations of suspected black holes)

15. Life Cycles of Stars Did we get there… Can you…
Name the process and fuel used by stars.
Describe the life cycle of a low mass star.
Describe the life cycle of a intermediate mass star.
Describe the life cycle of a high mass star.
What is a black hole?
Assignment: Origin of a Star (Concept Map)