A lesson I gave to high school students during my time at Yale, with the Yale SPLASH student organisation.

1. What are dead
stars good for?
Wee Jerrick | Yale Splash 2018

2. White Dwarfs Black HolesNeutron Stars

3. How are stars born?

4. A cloud of gas.

5. Newton’s Law of Universal Gravity
M1M2
F =
r2
G

6. M1
M2
F2
F1
r

7. M1
M2
F2
F1
r

8. M1
M2
F2
F1
r

9. Mass-Energy Equivalence
E = mc2

10. Nuclear fusion:
manufacturing the
materials of the world

11. Just for fun:
The sun consumes 6 x 1011 kgs of hydrogen per second.
The energy-production efficiency of nuclear
fusion from hydrogen to helium is 0.7%—
i.e. 0.7% of mass is converted to energy.
How much energy does the sun produce a second?
E = mc2

12. Equilibrium
Compressive/Attractive force
of gravity
=
Expansive force of energy
released from nuclear fusion

13. Animation of
gaseous collapse

14. The four stages of a star’s life
Birth Main
Sequence
Giant
Phase Death

15. Sun-like
(average) stars
Big, massive stars

16. A sun-like star
Type
Mass
G
1.989 x 1030 kg
or 1 M☉
Hydrogen -> Helium
4He
1H

17. Giant Phase
Predominantly Helium
Nuclear Fusion coming to a halt

18. Death: Planetary
Nebula
Gravitational Collapse halted by
the formation of a white dwarf
Material falling towards the core
bounces back out to space (creating
a “planetary Nebula”)
White dwarf is left behind

19. Ring Nebula

20. Big, big stars
Type
Mass
B and above
> 8M☉

21. 56Fe
28Si
16O, Ne
12C, 16O
4He
1H, 4He
A 20M☉ star in late main-sequence
would have this nested sequences
of zones in its interior.
It first fuses H -> He, then He -> C,
and C-> O and so on. The lighter
elements are pushed out of the
core (rather than heavy elements
sinking in).
As nuclear fusion beyond iron takes
in more energy than it produces, the
fusion process stops at iron.

22. Death: Supernova

23. Death: Supernova
Gravitational collapse halted by
the formation of a neutron star
Material falling towards the core
bounces back out to space
The neutron star is formed by
inverse beta decay, where protons
combine with electrons to form
neutrons.

24. Cassiopeia A
Can you spot the neutron star?

25. Death: Supernova
Instead of a neutron star,
if a star is particularly massive,
a black hole is created instead.

26. White Dwarfs Black HolesNeutron Stars

27. White Dwarf
Made of a degenerate carbon-oxygen
material
Held up and resists further gravitational
collapse due to the electron degeneracy
pressure
The limit that it can hold itself up is
governed by the Chandrasekhar mass
limit of 1.44M☉
Approx. 6000km in radius
(about the size of Earth)

28. Made of a degenerate neutrons; they are
the densest objects in the Universe
Held up and resists further gravitational
collapse due to the neutron degeneracy
pressure
The limit that it can hold itself up is
governed by the Tolman–Oppenheimer–
Volkoff (TOV) Mass Limit of 2.17 M☉
Approx. 10km in radius
(smaller than New Haven)
Neutron Star

29. Has an escape velocity > c
Nothing holds it up—it collapses within
itself.
There is no limit to how massive or “big”,
a black hole can become.Black Hole

30. What are these dead
stars good for?

31. White Dwarfs Black HolesNeutron Stars
Become black dwarfs
Grow black too
Evaporate to nothingness

32. 1.
They manufacture the material
that makes life possible.

33. Collision/Merger Event
Explosion of a
White Dwarf
Explosion of a
Neutron Star

34. Type Ia Supernova
The thermonuclear explosion of a white dwarf.
Happens when a white dwarf gains mass and loses
stability from the extra mass (~1.4 M).
The white dwarf is completely obliterated.
Creates most of the iron (Fe-56) in the Universe,
and other elements, such as Ca, V, Ni, Cu.
Is life possible without iron?

38. Kilonova
A thermonuclear explosion caused by the
merger of two neutron stars.
A black hole is believed to be formed after
the merger
Creates almost all of the platinum, gold,
uranium, thorium, iodine, xeon, and
other heavy elements in the universe.

39. A Neutron Star-Neutron Star Merger

40. Question:
Are black holes good for anything?

41. 2.
They help us to understand the
extremes of physics.

42. Crab Nebula in
Visible Light

43. Something in the
centre of the Crab Nebula,
spinning 30 times a second.
What on earth could that be?

45. Sun White Dwarf Neutron Star Black Hole
Einstein’s General Theory of Relativity
Also: my hopes
and dreams

47. 3.
They allow us to measure
astronomical distances.

48. Big Question:
How do you measure distances
to objects in space?

51. Calculating (big) distances in space:
m - M = 5 log (d/10)
We use the Distance Modulus:

52. m - M = 5 log (d/10)
Apparent brightness
Absolute brightness
Distance

53. Nearby
Far away
(both objects are the same size)

54. Absolute Brightness
Apparent
Brightness
(both objects are the same size)

55. White Dwarf
Made of a degenerate carbon-oxygen
material
Held up and resists further gravitational
collapse due to the electron degeneracy
pressure
The limit that it can hold itself up is
governed by the Chandrasekhar mass
limit of 1.44M☉
Approx. 6000km in radius
(about the size of Earth)

56. When white dwarfs explode, they
all produce the almost exactly
the same brightness!

60. SNooPy Modelling and Fit

61. m - M = 5 log (d/10)
Apparent brightness
Absolute brightness
Distance

62. m - M = 5 log (d/10)
11.320
-19.211
Distance
d = ?

64. The Universe is not just expanding;
the Universe is the rate of expansion
of the Universe is increasing.

65. The fate the Universe?
Big Crunch?
Big Freeze?
No!

66. THE BIG RIP

68. Wee Jerrick
weejerrick@gmail.com
https://astro.weejerrick.com