1. Birth and Death of Stars
The Life Cycle of Stars
28.3 page 628 :

2. The Hertzsprung-Russell diagram isn’t just an orginazational chart for the the stars, but the life cycle of the stars!

3. Life Cycle of Stars

5. Stellar Careers The lives of the stars seem to be “predestined”
The MASS of a star determines …
what type of star it will be,
where it will be on the main sequence, and
how long it will live for.
What it will end up as at its death
Each type of star has a particular series of events during their lifetime.
Deaths can be spectacular!

6. The MASS of a star determines … what it will be

7. Stage 1 Nebula
The space between stars is filled with gas and dust. called a nebula
99% of interstellar matter is hydrogen.
Temperature: Cool
Eventually gas “clumps” and compress

8. Life Cycle of a Star
Death/old
young
nebula

9. Whatever the cause, the nebula begins to contract.
As the nebula collapses, the temperature and density increase.
As it contracts, it breaks into many clumps, which forms hundreds of stars of various masses.
The size of each clump determines the mass of the star that will form.

10. Joseph Howard

11. Clumps / fragmentation
These will become STARS

12. Stage 2 Protostar Still shrinking, getting denser
Temperatures increase
Core is contracting
Recognizable as a ‘star’
Has a photosphere surface

13. Life Cycle of a Star
Death/old
young
protostar
nebula

14. “Duds” or Failed Stars
Clumps without enough mass are too small to become stars
They just cool and compact to become brown dwarfs orbiting in space
Gas Giant planet Jupiter is a failed star.

15. Life Cycle of a Star Not enough mass to reach temps to fuse hydrogen
Death/old
young
Brown
dwarf
protostar
nebula
Not enough mass to reach temps to fuse hydrogen
“dud”
Gas giant planet: Jupiter

16. IF the protostar has enough temperature and luminosity to make it onto the H-R scale.
Its mass determines where it jumps on.

17. Stage 3 A Star is Born! When the core reaches 10,000,000 K
Nuclear FUSION begins
Hydrogen fuel is fusing into helium
A true star

18. Life Cycle of a Star fuse hydrogen fuel 100 billion yrs. Main sequence
Death/old
young
Brown
dwarf
protostar
nebula
Not enough mass to reach temps for fusion of hydrogen
Gas giant planet:
Jupiter
Main sequence
star
fuse hydrogen fuel
100 billion yrs.

19. Main Sequence, Hydrogen is fusing into helium
A star spends 90% of it’s life as a main sequence star.
This is it’s mature, adult stage.
Our Sun will be here for 10 billion years

20. Main Sequence at Last It reaches Equilibrium: its stable
The heat & pressure of the gas expanding outward balances
the GRAVITY that is
pulling the matter inward

21. Death of a Star

22. Life Span
Massive stars use up their fuel faster, so they spend less than a 1 billion years as a main sequence
The smaller mass stars spend
100 billions years as a main sequence star!

23. Life Cycle of a Star Death/old young Brown dwarf protostar nebula
Not enough mass to reach temps for fusion of hydrogen
Gas giant planet: Jupiter”
Main sequence star
100 billion yrs.
white dwarf black dwarf
Fusing hydrogen for fuel

24. Stage 4: Running on Empty
Star is aging, hydrogen fuel is used up, and helium is building up in the core.
There is no heat to push out so gravity pushes in, the core becomes unbalanced and begins to collapse
As it collapses, temperature increase until it reaches 100,000,000 K!
Helium begins to fuse.
Heat generated in the core, It EXPANDS

25. The outer layers are expanding and cooling
It is now a RED GIANT
Star begins leaving the main sequence

26. Leaving the Main Sequence
It’s a
RED GIANT
It is cooler,
but bigger,
so it’s brighter

27. Stage 5 Planetary Nebula
Core continues fusion of helium.
When helium fuel is gone, the core shrinks
Outer gas layers are thrown-off as a
Planetary Nebula
Example: Planetary Nebula IC 418

28. Stage 6: The End
Red Giant
All that is left is the core
White Dwarf

29. White Dwarf All that’s left is the core: very small (earth size),
very dense (200 x’s more dense than Earth!),
very HOT (100,000 K) core
It will slowly cool over a billion years.

30. Life Cycle of a Star Death/old young Brown dwarf protostar nebula
Not enough mass to reach temps for fusion of hydrogen
“dud”
Main sequence
white dwarf black dwarf
Fusing hydrogen for fuel
Red giant planetary white dwarf Black
10 billion yrs nebula dwarf
Hydrogen fuel fusing helium fusing
Main sequence

31. Red Super Giants Example: Betelgeuse
When the helium is fusing, temps increase, it expands, and becomes a super red giant and cools
Gravity contracts the core until its heated enough to begin burning the next element, carbon.
This process continues through the fusing of oxygen, neon, nickel, and silicon with the high mass star alternating between the blue giant phase and the red giant phase throughout.
Large stars repeat this expansion and contraction cycle up to 7 times as their core elements keep fusing until they reach iron.
When the core becomes iron fusion ends
Example: Betelgeuse

32. Supernova VERY MASSIVE stars: > 8 M
Supernova remnant
Supernova
VERY MASSIVE stars: > 8 M
When core collapses, density reaches astonishing 400,000,000,000,000 g/cm3
The core ‘overshoots’ its equilibrium point and rapidly ‘rebounds’
Core explodes in a high speed shockwave, blasting everything into space!
Crab Nebula, remnant of a supernova that exploded in 1054 A.D.
most astounding fact

33. Final Stage for Massive Stars (Neutron Star or Black Hole)
Stars less than 8 solar masses become dwarf stars (cool, dim, burnt out)
Stars 8 solar masses or greater become neutron stars or black holes
Neutron Star Black Hole

34. Neutron Star
When the iron core of a MASSIVE STAR is collapsing, it might stop. Leaving behind an extremely small, dense neutron star.
Extreme density 1018 kg/m3
Extremely small: size of a city
Spin! Can emit a beam and pulse: Pulsar

35. Life Cycle of a Star Death/old young Brown dwarf protostar nebula
Not enough mass to reach temps for fusion of hydrogen
Gas planet Jupiter
Main sequence
100 billion yrs
white dwarf black dwarf
Fusing hydrogen for fuel
Red giant planetary white dwarf black
10 billion yrs nebula dwarf
Hydrogen fuel fusing helium fusing
Main sequence
Neutron
Star
Black
hole
Main sequence Super red Supernova!
2-100 million yrs giant
Hydrogen – helium – carbon- neon – oxygen - silicon …

36. The END - Death Stars iMovie
Name of final object
Starting Mass
Time / Age / years
Description
Picture / Image
Name of a familiar star as an example