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Death of Stars
(for high mass stars)
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Remember: What a star evolves into depends
on its MASS.
After the main sequence, a star could
become.
White dwarfs (low masssize of sun or smaller)
pulsars (heavier starslike blue giants)
black holes (heaviest starslike blue giants)
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Review
Same as before, but faster
1. intersteller cloud of dust
2. protostar
3. main-sequence starbut as a BLUE GIANT
4. Red Supergiant-- When a high-mass star
exhausts the hydrogen fuel in its core the star leavesthe main sequence and begins to burn helium.
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The Structure of the Core
of a Star Just Before It
Erupts as a Supernova
When helium is depleted, fusion of
heavier elements begins. This process iscalled nucleosynthesis.
H -> He -> C -> O -> Si -> Fe
(eventually goes to IRON)
When the final product is iron in the core,
no more energyso it collapses.
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Why is iron (mass number = 56) the
last stage?
Atoms will
naturally fuse
into more
stable nuclei
You cant get
more energy
out of fusing
iron
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B. Carbon core
contracts causing
1. Pressure to rise 2. Temp. to rise to 600
million K
C. Higher temps.Cause carbon fusion
cycle that will
eventually end in iron.
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Steps in the Explosion of a Supernova
D. formation of iron ends the fusion cycle and starcontracts one last time and rebounds off the dense
core
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Kaboom!
1. Luminosity--
100 billion times
brighter than thesun
2. produces wave
of neutrinos,
elements heavier
than Fe, shock
waves in nebulae
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SN 1987A
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Supernova
G. Example: SN
1987A
1. Where? --in LargeMagellanic Cloud (S.
hemisphere)
2. When?--1987 (duh)
3. What was found?--
neutrinosas the
theory predicted
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Neutrino detector
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The Brightness of a Typical Type II
Supernova for 100 Days After the Supernova
Reached Maximum Brightness
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Neutron Stars
A. Description
1. Extremely dense star after
shedding outside layers
2. Mass is about 1.4 to 3
solar masses
3. Size is about 10 km
across (small!)
4. Density is about 3 x 1014g/cm3 ( 1cm3 of neutron star
equals 340 m3 of steel!!!)
(artists rendition)
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Pulsars 1. Pulsars are neutron starsthat rotate
a. NOT normal starsthe
rotation period is 0.001 to
10 seconds (fast!)
2. Have extremely intense
magnetic fields
a. result--rips apart particles
at surface
b. accelerated electrons emitsynchotron radiation
c. like a lighthouse
3. Why do they spin?--
because big to small spinsfaster
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A Model of a
Pulsar
We can maybe
see them if we
are lined up
with the
beams of
radiation
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Crab Pulsar Animation
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One Hundred
Consecutive Pulses
fromPSR 1133+16
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Crab Pulsar
Ex. Crab Pulsar inside
the crab nebula
The pulsar is withinthe left over
supernova remnant
from 1054 A.D.
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So What Effect does Gravity
have on spacetime? Spacetime has 4 coordinates:
x-axis, y-axis, z-axis (3-D) and time
Mass bends spacetime in general. (Einstein)
Black holes (supermassive) bend spacetime a
lot !
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Flat and Curved Two-Dimensional Spaces
P th f M bl d th T l i i
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Paths of a Marble and the Television
Image of the Paths for the Cases of
Flat and Curved Space
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Black HolesA. Not really a holeB. A dense star that continues
to collapse
1. So dense and gravity is so
strong that light cant escape
C. Event horizon--ring around
black hole where lightcouldnt escape
D. Scharzshild radius--the
radius a star has to have to
become a black hole
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Black holes
1. For sun to become a black hole--it would
have to collapse to at least 3 km
2. For the earth to become a black hole--it
would have to collapse to 1 cm
Th P th f Li ht R Ai d O t d
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The Paths of Light Rays Aimed Outward
in Different Directions from the
Collapsing Core of a Star
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A visual diagram of
how a black hole may
bend spacetime.
However, you dont
see this (its not like
a waterslide).
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Artists drawing of a black hole If we cant see
them, how do we
know they are there?
1. Accretion disk 2. Galactic jets
3. X-rays from the
disk
4. A companion star
orbiting nothing
Note: The bright center is
not the black hole, justener etic material around it.
Galactic jets
Accretion diskX-rays
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Cygnus X-1
Distance--2500 pc
(8000 ly away)
where?--inconstellation Cygnus
discovered in 1966
a. blue supergiant
companion that orbits
it
b. intense x-rays (as
seen in picture)
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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http://aspire.cosmic-
ray.org/labs/star_life/hr_interactive.html
http://aspire.cosmic-ray.org/labs/star_life/hr_interactive.htmlhttp://aspire.cosmic-ray.org/labs/star_life/hr_interactive.htmlhttp://aspire.cosmic-ray.org/labs/star_life/hr_interactive.htmlhttp://aspire.cosmic-ray.org/labs/star_life/hr_interactive.htmlhttp://aspire.cosmic-ray.org/labs/star_life/hr_interactive.html