Star Death
LACC §: 22.1, 22.2, 23.5
• White Dwarfs (Chandrasekhar limit = 1.4
Msolar): the dead carbon cores of low mass
(<~10 Msolar) stars after a Planetary Nebulae
• Neutron Stars and Pulsars (1.4 < 3 Msolar):
remnants of high mass (>~10 Msolar) stars after
a Type-II Supernovae
• Black Holes (>3 Msolar): remnants of high mass
(>~10 Msolar) stars after a Type-II Supernovae
An attempt to answer the “big questions”: What is
out there? Where did I come from?

HR Diagram
http://outreach.atnf.csiro.au/education/senior/astrophysics/stellarevolution_hrintro.html

Low Mass Evolution
http://www.physics.uc.edu/~hanson/ASTRO/LECTURENOTES/W07/Death/Page1.html

Planetary Nebulae
With some complications
glossed over, the envelope
and as much as 50% of the
stellar mass is detached
from the star and expelled
into space leaving the AGB
star very hot core
exposed.
The high temperature of the "central star" (it is not REALLY a star as
there is no fusion energy source) means it has a Planck [or thermal
spectrum] curve that peaks way out in the UV and produces many UV
and even soft X-ray photons. These collide with the H, He, C and O
atoms in the former envelope that we now call a PN. These atoms get
ionized, and on recombination the e- drop through the energy levels
giving off various lower energy photons (that add up in energy to the
original UV or X-ray ionizing photon) as they head for the ground state.
http://www.ucolick.org/%7Ebolte/AY4_00/week7/low-mass_deathC.html

Planetary Nebulae
http://rst.gsfc.nasa.gov/Front/pne.jpg

Planetary Nebulae: A Dying
Low Mass (<~10 Msun) Star
http://oposite.stsci.edu/pubinfo/pr/96/13/Helix.mpg

Type-II
Supernova
http://www.williams.edu/
astronomy/Course-Pages/111/
Images/SN/sn_explosion.gif

Supernova 1987a
http://cse.ssl.berkeley.edu/bmendez/ay10/2000/cycle/snII.html

Type-II Supernova
http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/supernovae.htm

Supernova Light Curves
http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/supernovae.htm

Enrichment of the
Interstellar Medium
Gas is recycled in the Galaxy.
It goes into forming stars and
is returned during the death
throws of stars enriched with
heavy elements for the next
generation of stars. It is a
giant cycle of life.
http://cse.ssl.berkeley.edu/bmendez/ay10/2002/notes/lec16.html

Enrichment of the
Interstellar Medium
Binding energy plot: the graph
shows the nuclear binding energy
per nucleon (i.e. per proton or
neutron).... For increasing atomic
number the binding energy
increases (in this plot, downwards),
until it reaches its maximum for
iron-56. The nucleosynthesis from
hydrogen to iron-56 is energetically
favorable and occurs through
consecutive fusion reactions.
If you want to climb the rest of the periodic table, then new
mechanisms...are needed. Note that one can go in the opposite
direction (from heavy to light nuclei) through nuclear fission.
http://www.scienceinschool.org/2007/issue5/fusion

Stellar Remnants
neutron degeneracy
electron degeneracy pressure pressure
http://www.maa.mhn.de/Scholar/Starlife/evolutnc.html

White Dwarf:
Mass-Radius Relationship
About 15 km
About 10,000 km
http://ircamera.as.arizona.edu/NatSci102/lectures/whitedwrf.htm

Stellar Remnants
Density: ~0.5 tons/cc
About 15 km
About 10,000 km
Density: ~100,000,000 tons/cc
http://astro.ucc.ie/research/intro/index.html

Stellar Remnants: Black Hole
Note that the Schwarzschild radius scales with the mass of
the black hole. The Schwarzschild radius of a 1 solar mass
black hole is 3 x 105 cm [3 km, less than 2 miles].
http://www.astro.cornell.edu/academics/courses/astro201/bh_structure.htm

Neutron Stars / Pulsars
What a star becomes
when it dies depends on
the mass left when all
possible nuclear fuels are
exhausted and the star
has lost some of its
original mass by ejecting
it:
M <= 1.4 M -----> white
dwarf/planetary nebulae
1.4 M <M < ~3 M -->
neutron stars/pulsars
M > ~ 3 M ---->
supernovae/black holes
Pulsar Animation
http://ircamera.as.arizona.edu/NatSci102/lectures/whitedwrf.htm

The Crab Nebula/Pulsars
This picture shows a time
sequence for the pulsar in the
Crab nebula, shown in context
against an image.... Both the
nebula and its central pulsar were
created by a supernova explosion
in the year 1054 A.D. The
enlarged region is a mosaic of 33
time slices, ordered from top to
bottom and from left to right.
Each slice represents
approximately one millisecond in
the period of the pulsar. The
brighter, primary pulse is visible in
the first column: the weaker,
broader inter-pulse can be seen in
the second column.
http://hera.ph1.uni-koeln.de/%7Eheintzma/NS1/SN1054.htm

What would a naked black hole
look like? Maybe...
“A (simulated)
Black Hole of
ten solar
masses as
seen from a
distance of
600 km with
the Milky Way
in the
background
(horizontal
camera
opening angle:
90°).”
http://www.tutorgig.com/ed/black_hole

http://www.spitzer.caltech.edu/Media/happenings/20050526/

Gamma-Ray Bursts
James Annis, an astrophysicist at
Fermilab, near Chicago, has speculated
that such events could sterilize entire
galaxies, wiping out life-forms before
they had the chance to evolve to the
stage of interstellar travel. 1 "If one went
off in the Galactic center," he wrote, "we
here two-thirds of the way out of the
Galactic disk would be exposed over a
few seconds to a wave of powerful
gamma rays." It would be enough,
according to Annis, to exterminate every
species on Earth. Even the hemisphere
shielded by the planet's mass from
immediate exposure would not escape,
he claimed, since there would be lethal
indirect effects such as the demolition of
the entire protective ozone layer. The
rate of GRBs in the universe today
appears to be about one burst per
galaxy per several hundred million years.
http://www.daviddarling.info/encyclopedia/G/gamma-ray_burst.html

X-ray binaries & X-ray bursters
http://www.roe.ac.uk/roe/support/pr/pressreleases/050608-ultracam/
index.html

Millisecond Pulsars
This animation attempts to condense the
billion year evolutionary history of such a
binary system into a few tens of seconds.
It begins with two stars, one more
massive than the other, in a tight orbit.
The massive star evolves first and
swallows up its companion, which spirals
into it forming an even tighter binary system. The core of the massive
star produces a supernova and leaves behind a neutron star. The neutron
star's companion eventually begins to lose mass and forms an accretion
disk around the neutron star. The accretion of material onto the neutron
star causes it to spin faster and faster, eventually reaching a spin period of
a few milliseconds. The accreted material produces X-rays which in turn
can begin vaporizing the companion. All that remains at the end is a
highly compact, rapidly rotating neutron star which produces a pair of
radio beams and may be observable as a millisecond radio pulsar.
http://heasarc.gsfc.nasa.gov/docs/xte/Snazzy/Movies/millisecond.html

Review for the Test (4 of 5):
Stars
[10 pts] The Sun • mass & age & main sequence: high mass at top
• proton-proton chain, the neutrino problem left, short lifetimes; low mass at lower right and
• interior → atmosphere: core, radiation zone, long lifetimes; main sequence turn-off point
convection zone, photosphere, chromosphere,
corona, solar wind [10 pts] Stellar Evolution
• solar phenomena (solar magnetic field): granules • low mass stars: Hayashi track, main sequence (H
sunspots, flares, prominence/filaments, coronal core burning), red giant branch (H shell burning),
mass ejection, aurora (on Earth) [pictures] helium flash (He core ignition), horizontal giant
branch (He core burning), asymptotic giant branch
[10 pts] Stars (He shell burning), planetary nebulae (envelope
• stellar spectra: temperature, spectral class, radial ejection), white dwarf
velocity (red-shift vs. blue shift), composition, • high mass stars: similar to low mass stars, but
spectral class keep fusing elements up to iron, type-II supernova
• determining distances: radar (closest planets), (gamma ray burst), neutron star (pulsar) or black
stellar parallax, standard candles--e.g. main hole
sequence fitting, RR Lyrae and Cepheid variables • nebulae: molecular clouds, HII regions (planetary
• other properties: proper motion, luminosity, nebulae, supernova remnants), reflection nebulae
apparent brightness/magnitude vs. absolute [pictures]
brightness/magnitude, spectroscopic or eclipsing
binaries to determine mass [10 pts] Binary Systems & Stellar Remnants
• nova and type-I supernova: binary system with a
[10 pts] The Hertzsprung-Russell Diagram white dwarf, light curves
• axes: x-axis = temperature, spectral class; y-axis = • X-ray binaries and X-ray bursters: binary system
luminosity, absolute magnitude with a neutron star or black hole, accretion disks
• regions in the HR Diagram: main sequence, white • stellar remnants: masses, sizes, densities of white
dwarfs, giants, supergiants, luminosity class dwarfs vs. neutron star vs. black holes; pulsars;
black holes (singularity, Schwarzschild radius,
event horizon)

LACC HW: Franknoi, Morrison, and
Wolff, Voyages Through the Universe,
3rd ed.
• Ch. 22, pp. 509-511: 8.
• Ch. 23, p. 532: 4.
Due at the beginning of next class period.
Test covering chapters 14-23 next class period.