1. The Life and Death of Stars
The Universe
The Life and Death of Stars

2. WHAT IS A STAR?
STAR:
sphere of _______________________________________________
emits __________________________________________________
the sun is a _________________________________________________to Earth
LIGHT-YEAR: distance that light travels in one year - about 9.5 trillion kilometers
Earth is 8 light-minutes from the Sun

3. POWERING STARS WITH STAR FUEL
NUCLEAR FUSION REACTIONS: the nuclei of _____________________________ (H) atoms combine into
_____________________________ (He) atoms.
When two particles fuse, __________________________ is released.
Takes place in the ________________________________________
Core = extremely ________________, extremely ________________,
and under extreme _________________________ (perfect for fusion)

4. At _________________in the core of the star, fusion ignites!
NUCLEAR FUSION BASICS
At _________________in the core of the star, fusion ignites!
______________________ atoms smash into each other -->
______________________ atom + particles + ____________
Where does the energy come from?
Mass of four 1H atoms > Mass of one 4He atom
Extra mass in converted to energy
E = mc2
(Energy) = (mass) x (speed of light)2

5. OUR STAR – THE SUN
Converts _________________________________of hydrogen to helium every second
Converts 4.7 million tons of ____________________________________ every second
We receive two billionths of that energy here on Earth - ____________________
Enough to power 100 light bulbs for 5 million years
The sun formed about __________________________years ago.
__________________________________________= size of the Sun
Example: 3 solar masses = size of 3 Suns

6. Think! What is a star? (In your own words)?
Why is our sun a ‘star’ and NOT a ‘planet’?

7. WE STUDY STARS BY STUDYING LIGHT Brightness of a Star
Depends on the star’s _________________________________________________________
The brightest star in the night sky = ____________________________ (Because relatively close to Earth, 9 light years)
Stars produce not only visible light but all types of __________________________________________________
Gamma Rays, X-rays, Ultraviolet, Infrared, Microwaves, and Radio waves.
Scientists use special telescopes and satellites to see the different types of radiation coming from the stars

8. STUDYING STARS TEMPERATURE
A star’s _____________ is related to its _________________
____________________ objects glow with __________________ light
that has ___________________________ wavelengths.
that has ___________________________ wavelengths

10. The Hertzsprung- Russell Diagram (H-R Diagram)
1911: Danish astronomer Ejnar Hertzsprung compared and plotted magnitude of stars with their color (temperature)
1913: American astronomer Henry Norris Russell plots stars’ spectral class against magnitude

11. Together, the plots show a relationship between and .
Shows that stars fall into

16. Life Cycle of a Main Sequence and Massive Star
STAGE 1
STAGE 2
STAGE 3
STAGE 4
STAGE 5
Main Sequence Star

17. STAR LIFE CYCLE: STAGE 1 – BIRTH MAIN SEQUENCE AND MASSIVE STARS
All stars begin their life the same
They form from a Stellar Nebula = Cloud of ____________________ at beginning of star life cycle
Steps that lead to the birth of a star
_______________________________________causes the gas and dust to accumulate (this is called accretion)
A __________________________ forms (not yet a star)
Temperature and pressure _______________________ until nuclear fusion begins (now a star)
Nuclear fusion beginning means that a star has been born

18. STAR LIFE CYCLE: STAGE 2 – MIDDLE AGE MAIN SEQUENCE AND MASSIVE STARS
Nuclear Fusion has begun and continues…
Hydrogen fuses into helium and releases lots of energy
The fusion reactions in the core of the star produce an
_________________________________________that balances the
_________________________________________due to gravity.
Massive Stars = _____________________ fusion rates
More gravity = hotter cores = uses hydrogen faster
Over time, the percentage of the star’s core that is helium becomes __________________________.
After millions of years, core will _______________________ of hydrogen and star will begin to die.

19. STAR LIFE CYCLES: STAGE 3 - DYING
MAIN SEQUENCE STAR
LIFE CYCLE
As fusion slows, the outer layers of the star will _______________________
Becomes a red giant
RED GIANT:
10 to 100 times larger
Converts helium to _________________________
When the star _________________________of helium, fusion stops, outer layers will expand, and leave the star’s orbit.
MASSIVE STAR
LIFE CYCLE
As fusion slows, the outer layers of the star will cool and expand
Becomes a supergiant
SUPERGIANT:
________________________ times larger
Converts helium to carbon, oxygen, and…
Has enough mass (gravity) so heavier elements can fuse into __________________

20. STAR LIFE CYCLES: STAGE 4 – DEATH
MAIN SEQUENCE STAR
LIFE CYCLE
Fusion stops at helium
Outer gas layers from red giant stage are released to form ______________________
PLANETARY NEBULA:
Cloud of gas and dust at end of stars life cycle
Sends enriched elements into space
When the planetary nebula clears, a ________________ is left (part of Stage 5 for a Main Sequence Star)
MASSIVE STAR
LIFE CYCLE
Supergiants can fuse heavier elements beyond helium
Fusion stops at iron
Develop layers of different elements with iron at the _____
Iron will not fuse
Force of gravity becomes greater than force of fusion
Eventually the core _________________________ and then explodes in a Type II supernova.
SUPERNOVA: a gigantic explosion in which a massive star collapses and throws its outer layers into space

21. Layers of heavy elements in a supergiant

22. STAR LIFE CYCLES: STAGE 5 – AFTER DEATH
MAIN SEQUENCE STAR
LIFE CYCLE
When planetary nebula clears, a white dwarf is left
WHITE DWARF:
a small, hot dim star that is the _______________________ of a main sequence star.
Very dense - _______________________
Will cool until it becomes a black dwarf (no more light, big lump of coal)
MASSIVE STAR
LIFE CYCLE
After a Type II supernova, either
(A) ________________________ or
(B) ___________________ forms.
If the remaining core has a mass of __________________ solar masses = neutron star (densest star).
If the core has a mass that is ______________ solar masses = black hole.
BLACK HOLE: an object so massive and dense that not even light can escape its gravity
NEUTRON STAR: composed of neutrons, 1 teaspoon would weigh 5 x 1012 kg

23. Think! What are the 5 stages of star life?
How are these stages similar and different to human life?

24. WHY DO WE CARE ABOUT STARS?
We get all elements _________________from fusion in stars
We get all elements heavier than Iron from ______________
Without stars, we wouldn’t have:
___________________________ which make up our body
___________________________ needed to sustain life