Transcript 1. Neutron stars 2. Black holes

High mass endings
Answers from you folks on yesterday’s
quiz.
Differences between a dying low mass vs. a dying
high mass star:
 No He flash in a high mass star death.
 Low mass stars end in white dwarfs, high mass
stars end in supernovae.
 Heavy elements formed in death sequence of a
high mass star.
 Low mass stars end in white dwarfs with planetary
nebulae around them.
 The weight watcher rule: big things go early,
smaller things live longer.
Good Job. Folks !!!!!!
Large mass stars and the main sequence
What do they do on the main sequence?
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CNO cycle: Carbon, nitrogen, oxygen cycle
1.
High temperatures needed for this cycle to take
place (~ 15 million 0K).
2.
H is used along with C as a catalyst to produce
He atoms.
Large mass stars on the main sequence
continued…
3. Stay stable; hydrostatic equilibrium
4.
5.
6.
Main Sequence turn-off
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Almost the Same as with low mass star:
1.
Depletion of H in core
2.
He core contracts
3.
Temperatures rise igniting H layer
Increased pressure drives envelope of star outward
creating a super giant or giant.
This cycle repeats many times depending on mass.
When it does, at each new stage heavier elements are
created.
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As temperature
increases with depth,
the ash of each
burning stage
becomes the fuel for
the next stage.
So as each element is
burned to completion
at the center, the
core contracts again,
heats again, and so
on…
Once inner core turns
to Iron, fires cease in
the core, internal
outward pressure
dwindles and
hydrostatic
equilibrium is
destroyed. Gravity
takes over and……..
Fusion of heavy elements.
BanG !!!!!
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The star implodes! (falls in on itself!)
Core temperature rises again, all heavy elements in core
undergo Photodisintegration, undoing the fusion process of
the previous 10 million years. End up with electrons, protons,
neutrons, and photons in core.
Core compresses, stops and rebounds with a vengeance!
During this rebound, a shock wave sweeps through the star
blasting all the overlying layers, including the heavy elements
just formed outside the iron core into space: a Type 2
Supernova has occurred.
The brightness of a supernova may rival the brightness of
the entire galaxy in which it resides. This period is short ~
few days, maybe a month.
Big and little bangs
Novae and supernovae are two different types of beasts.
 A nova is an increase in the brightness of an accreting white dwarf star
that is undergoing a surface explosion.
 The temporary and rapid change in luminosity can occur over a period of
a few days.
 On the average, 2 or 3 novae are observed every year.
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As to type 1 supernovae, a star has to have a buddy for this to occur.
Type 1 supernovae and white dwarfs
When an accreting white dwarf exceeds a maximum value of 1.4
solar masses (Chandresekhar mass), electrons inside cannot
provide the pressure needed to support the star.
 Star begins to collapse, temperature rises to the point where
carbon fusion takes place.
 Fusion taking place everywhere throughout the star causes it to
explode – Type 1 supernova (carbon-detonation supernova).
 Star is believed to be blasted to bits
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Type 2 supernova remnant
Crab nebula
 A supernova
remnant.
 1st seen in 1054
A.D.
 1800 pc from
Earth.
 About 2 pc wide
 Has a neutron star,
pulsar..
Speaking of which =>
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Large mass star endings (chapter 22)
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What remains after a supernova (type 2)
explosion?
More than what you get from a type 1 explosion, that’s for sure!
1. Neutron stars
2. Black holes
Creatures of the deep
Neutron stars
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A ball (size: that of a large
city ~ 20 km) of neutrons
left after a supernova
explosion.
Density: 1017 – 1018 kg/m3 ,
weight: thimbleful of
neutron star material would
weigh 100 million tons.
Gravity extremely
powerful; you’d weigh a lot
more on this star!
Carry strong magnetic
fields.
Spin very fast! (a
consequence of the
conservation of angular
momentum)
Black Holes
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Chandrasekhar limit for a
neutron star: 3 solar
masses. Above this limit
the star cannot support
itself against its own
gravity – collapse.
General Relativity says
that this collapse punches
a hole in space-time called
a singularity.
This singularity is
surrounded by a an event
horizon, which defines the
absolute edge outside of
which a photon of light can
escape.
Lets look at neutron stars first;
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If you’re a neutron star
you can decide to
announce your presence
by becoming a Pulsar
Crab pulsar: Hubble telescope
Pulsar emission
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Extremely rapid
rotation and
combination of a
strong magnetic field
dictates signal
properties seen by us.
We see the pulses
when they sweep
across the Earth
Discovered by Jocelyn Bell, a
grad. Student at Cambridge University,
In 1967.
Her thesis advisor won the Nobel Prize for
it in 1974.
Black holes and the speed of light
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Special relativity says that the limiting speed in the
universe is the speed of light.
Black holes and curved space-time
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General relativity says that any mass creates a
dent or depression in space-time.
The bigger the mass, the greater the depression
Page 584 figure 22.15
Proof
proof
Deflection of starlight measured in 1919,
confirmed the general theory.
Planetary orbits deviate from Kepler’s
ellipses, they actually precess
So.. What happens around a Black Hole?
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Gravitational red
shift.
Light energy is
drained near the
event horizon.
No escape of
light/radiation
upon entering
event horizon.
Getting close to
event horizon,
causes
spagetification,
when you’re
stretched out long
ways.