There are two types of supernovae that originate from different stellar progenitors. Type I supernovae originate from white dwarfs that exceed the Chandrasekhar limit after accreting matter from a companion star. Type II supernovae originate from massive stars whose cores collapse into neutron stars after exhausting their nuclear fuel. Supernovae play an important role in generating elements heavier than iron through nuclear fusion and the r-process. For radiation from supernovae or gamma ray bursts to be dangerous to life on Earth, they would need to occur within 30 light years or 8,000 light years respectively. The nearest candidates are over 250 and 1 billion light years away.

1. Supernovas
Yaxk'in Ú Kan Coronado
IA-UNAM
Coronado@astro.unam.mx

2. SUPERNOVA
What is a supernova?
How dangerous are they to life on Earth?
How would the universe be different without
supernovae?

3. Life of a Butterfly
Caterpillar
Eggs
Pupa
Butterfly
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4. Life of a Butterfly
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5. Life of a Sun-like Star
Sun-like Star
Protostars
Red Giant
Planetary
Nebula
Star-Forming
Nebula
White Dwarf
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6. Life of a Massive Star
Protostars
Massive Star
Red
Supergiant
Star-Forming
Nebula
SUPERNOVA
Neutron Star
Black Hole
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7. Death of low-mass star
White Dwarf
White dwarfs are the remaining
cores once fusion stops
Electron degeneracy pressure
supports them against gravity
Cool and grow dimmer over time
Pressure is independent of
Temperature.

8. A white dwarf can accrete mass
from its companion

9. Death of median-mass star
Neutron star
●
●
●
Compact and dense
objects compose of
neutrons (10¹⁷ g/cm³)
Over 1.44 M sun
(Chandrasekhar
limit), less to 3 M sun.

11. Neutron stars and pulsars
●
In 1967 Jocelyn Bell
discovered very
rapid pulses of
radio emmision
coming from a
single point on the
sky.
–
The pulses were
coming from a
spinning
neutron star -a
pulsar.

12. Pulsar at
center of the
Crab nebula
pulses 30
times per
second

13. Pulsars

14. Thought Question
Could there be neutron stars that appear as pulsars to
other civilizations but not to us?
A. Yes
B. No

15. Thought Question
What happens if the neutron star has more
mass than can be supported by neutron
degeneracy pressure?
1.It will collapse further and become a black
hole
2.It will spin even faster, and fling material out
into space
3.Neutron degeneracy pressure can never be
overcome by gravity

16. Neutron degeneracy pressure can no longer support a
neutron star against gravity if its mass is > about 3 Msun

17. Tycho’s supernova of 1572

20. ●
Supernovae
outshine the
whole galaxy!

21. Two kinds of supernovae
Type I: White dwarf supernova
White dwarf near 1.4 Msun accretes matter from red giant
companion, causing supernova explosion
Type II: Massive star supernova
Massive star builds up 1.4 Msun core and collapses into a
neutron star, gravitational PE released in explosion

22. light curve shows how luminosity changes with time

25. r process and s process elements
Nuclear fusion in all stars only produces up to Fe-56
Slow neutron capture (s process) forms up to Bi-209
in low-mass stars
High temps in SN creates elements up to Ca-254
Rapid neutron capture (r process) create neutron-rich
isotopes which decay into more stable neutron-rich
elements
Neutron flux during SN is 1022 neutrons per square
centimeter per second
neutron captures occur much faster than decays

28. Supernovae and nucleosynthesis of
elements > Fe
Movie

29. Tarea
●
●
●
●
Explica en cinco renglones ¿Por qué existen
dos tipos de supernovas de acuerdo a las
observaciones? ¿Tienen el mismo o diferente
origen.
Explica como se forma una SN-I A.
Investiga ¿Quienes ganaron el premio nobel en
2011? y ¿Cuál es su aporte en relación a las
SN-I A? ¿Por que usaron estas SN y no otras?
Explica como se generan los elementos más
allá del Fe en una SN.

30. Tarea Extra:
●
●
Asistir la congreso nacional de astronomía, en
el MUTEC del 29 de Oct. al 1° Nov.
–
Presentar una crónica del evento relatando tres
platicas de 20 min o una plenaria
–
Agregar aparte una opinión de lo que
aprendiste de este evento.
–
Describir en que consistía el poster que más te
gusto.

31. Gamma Ray Burst (GRB)

32. Is radiation from supernovae
and GRB sources
dangerous to Earth?
How close would they have to be?

33. Radiation on Earth
Radioactive sources emit
gamma-rays.
If we are too close to a
radioactive source, like a
chunk of uranium, we
cannot see the radiation, but
it is still harmful to us!
So how far should Earth be
from cosmic radiation
sources to be safe?
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34. Death from Exploding Stars?!
.
Artist’s
Conception
of the Milky
Way Galaxy
Location of Solar
System
35

35. How close would a Supernova
have to be?
.
Location of Solar
System
36

36. How close would a Supernova
have to be?
.
Location of Solar
System
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37. How close would a Supernova
have to be to be dangerous?
.
Supernova:
within 30 light
years
Location of Solar
System
Nearest Supernova
Candidate: over 250 light
years away!
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38. How close would a
Gamma-Ray Burst (GRB)
source have to be?
.
Location of Solar
System
39

39. How close would a
Gamma-Ray Burst (GRB)
source have to be?
.
GRB Danger Zone: within
8,000 light years
Location of Solar
System
40

40. How close is the nearest
Gamma-Ray Burst (GRB) source ?
Nearest detected GRB source: over
a Billion light years away!
.
Our galaxy is about 100,000 light years across
GRB
Danger
Zone
Location of Solar
System
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41. Today we know the
universe is filled with
powerful cosmic
radiation our eyes
cannot see:
• Gamma-rays
• X-Rays
• Fast-moving atomic
particles (“Cosmic Rays”)
Much of which originates from monstrous black holes in
the centers of galaxies and from . . .
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