Download Stars: HR Diagaram Stellar Evolution Astronomy 1 — Elementary Astronomy LA Mission College

Stars: HR Diagaram
Stellar Evolution
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
Quotes & Cartoon of the Day
“Ancient stars in their death throes
spat out atoms like iron which this
universe had never known. ... Now
the iron of old nova coughings
vivifies the redness of our blood.”
— Howard Bloom
“In the vast cosmical changes, the
universal life comes and goes in
unknown quantities ... sowing an
animalcule here, crumbling a star
there, oscillating and winding, ...
entangling, from the highest to the
lowest, all activities in the
obscurity of a dizzying
mechanism, hanging the flight of
an insect upon the movement of
the earth...”
— Victor Hugo
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Announcements
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SS Homework posted, due 11/19
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I will drop the lowest midterm grade
Schedule has been revised, final midterm now 12/3,
Thursday after thanksgiving
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If you miss midterm 3, that will become your drop grade
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unless you have a VERY good reason
Very, very good
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Last Class
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Intro to Stars
Temperature, Color & Size
Stellar Classification
Intro to the HR Diagram
LT HR Diagram
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
This Class
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Midterm Debrief
Stellar Classification (review)
Intro to the HR Diagram
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LT HR Diagram
Stellar Evolution
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Main Sequence
Red Giants and Supergiants
Endgame (time permitting)
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Low mass stars— planetary nebulae, white dwarfs
High mass stars — supernovae, neutron stars, black holes
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Midterm Debrief
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
Results
Letter
Current Course Grade
Midterm 2
A
11
3
B
15
6
C
17
14
D
1
12
F
5
13
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Review of Classification
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
The Harvard Computers
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The director of the Harvard Observatory from 1877 to
1919, Edward Charles Pickering hired women to
process astronomical data.
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They were cheaper than men
earned less than a clerical worker
Willamina Fleming had been his maid
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The Harvard Computers
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"Pickering's Harem" or “the Harvard Computers” included several
now-famous astronomers
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Annie Jump Cannon,
Henrietta Swan Leavitt
Antonia Maury
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Modern Classification
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Harvard spectral sequence
Developed by Annie Jump Cannon
Characteristic absorption lines determine stellar class
Note: in Astronomy “metal” means anything “heavier” than
He
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Modern Classification
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Cecilia Payne (PayneGaposchkin) discovered this
was actually a temperature
sequence
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More precise than BB peak or
color
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Spectral Classification
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From hot to cool:
OBAFGKM
Each spectral class is further divided into 10 ranges
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according to temperature. 0 = hot, 9 = cool
therefore O0 is the very hottest, and O9 is slightly hotter than
B0 and M9 stars are very cool
This is still a temperature-based classification
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Let’s Practice
Star Rue is Type K, Star Peeta is Type B, Star Katniss
is Type F and Star Primrose is Type M.
Which star is cooler than Rue?
A. Peeta
B. Katniss
C. Primrose
D. None of them
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
You observe a very bright, bluish star. It’s spectral
classification is most likely ____.
A. B
B. G
C. M
D. More information is needed to determine this
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
H-R DIAGRAM
Spectral Class isn’t everything
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Spectral Class is not
sufficient to uniquely
identify a type of star
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The supergiant
Arcturus and the red
dwarf Proxima Centauri
are both Type M &
3500 K
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They are definitely not
identical!
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Hertzsprung and Russell
http://outreach.atnf.csiro.au/education/senior/astrophysics/stellarevolution_hrintro.html
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In 1911 Danish astronomer, Ejnar Hertzsprung, plotted the
absolute magnitude of stars against their color
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Independently in 1913 American astronomer Henry Norris
Russell plotted spectral class against absolute magnitude
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showed that the relationship between temperature and
luminosity of a star was not random
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The H-R Diagram
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H-R diagram plots Color and/or Temperature
against Luminosity and/or Absolute magnitude
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Any data plotted like this is an H-R diagram, as is a
theoretical version
The H-R diagram is one of the most important tools
in Astronomy
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The Main Sequence
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The long strip from
upper left to lower
right is called the
“Main
Sequence.” (MS)
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Stars spend most of
their existence on the
MS
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91% of nearby stars are
MS stars.
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MS stars are fusing H
into He in their cores.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Giants and Dwarfs
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
WARM-UP QUESTION
Star A has an absolute magnitude of -8.1 and belongs
to spectral class B8. Star B has an absolute magnitude
of 11.2 and also belongs to spectral class B8. Which
star has the higher temperature?
A. Star A
B. Star B
C. They have the same temperature.
D. There is not enough information to determine
which star is hotter.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
LECTURE-TUTORIAL ON THE HR DIAGRAM
Star A has an absolute magnitude of -8.1 and belongs
to spectral class B8. Star B has an absolute magnitude
of 11.2 and also belongs to spectral class B8. Which
star has the higher temperature?
A. Star A
B. Star B
C. They have the same temperature.
D. There is not enough information to determine
which star is hotter.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Let’s Practice
A red giant of spectral type K9 and a red main
sequence star of the same spectral type have the
same _____.
A. luminosity
B. temperature
C. absolute magnitude
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
What Type of Star is Aldebaran?
A. Red Giant
B. Main Sequence
C. Supergiant
D. White dwarf
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
What Type of Star is Vega?
A. Red Giant
B. Main Sequence
C. Red Supergiant
D. White dwarf
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Stellar Lifecycles
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
The H-R Diagram Reflects Evolutionary
Stages
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Main Sequence is “prime of life”
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The Main Sequence isn’t forever!
MASS is what
controls ultimate
fate
© NASA
MASS is what
controls MS
lifetime
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Life on the Main Sequence
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
The Main Sequence
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Stars spend most of
their lives on the main
sequence fusing H to
He in their core
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The pressure resulting
from the energy
released by the fusion
balances gravity
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the star is stable
Hydrostatic equilibrium
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
•
Stars on the Main
Sequence are in
Hydrostatic Equilibrium
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The radiation
pressure (outward) is
balanced by the
(inwards) pull of
gravity
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Pressure tries to blow it
apart, Gravity holds it
together
Astronomy 1 - Elementary Astronomy
Copyrighted, 1998 - 2011 by Nick Strobel http://www.astronomynotes.com/
Life on the Main Sequence -- Hydrostatic
Equilibrium
LA Mission College
Levine F2015
Energy Source Nuclear Fusion
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The Sun is a typical MS star
Powered by Thermonuclear fusion
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Converts H to He and energy
Requires extreme conditions
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Occurs only in star’s core
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Nuclear Fusion
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nuclei have protons &
neutrons
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protons + electric charge
like charges repel
closer they get, harder
they push apart
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Must force nuclei very
close, then nuclear force
binds together
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Temp over 10,000,000 K
required
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Energy is released
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Image: http://www.thecollapsedwavefunction.com/
2013/02/nuclear-fusion-and-why-its-awesome.html
(for nuclei lighter than iron)
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The Proton-proton Chain
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Image: http://theamateurrealist.com/2014/10/02/from-the-suns-core-toearths-thermosphere/ (creative commons)
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Net reaction 4 H → He + energy
He has less mass than 4 H
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Mass is converted to energy
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about 0.7% “missing”
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Einstein’s mass-energy relation E=mc
In Sun, happens 10
38
Astronomy 1 - Elementary Astronomy
times per second
LA Mission College
Levine F2015
Rate of Mass-Energy Conversion
© 2015 by Sidney
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1038 reactions per second consumes 6 x1011 kg per
second
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600,000,000 metric tons
Sun’s mass is very large! (2x1030 kg)
0.00001% per million year
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Low Mass and High Mass Stars
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Low mass: less than about 4x Sun’s mass
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Sun is good model
use the proton proton chain
High mass:
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use the CNO cycle rather than the p-p chain
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same net result 4H->1He
different set of reactions
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Let’s Practice
It takes extreme physical conditions to initiate nuclear
fusion because _____.
A. nuclei have positive electrical charge and repel
each other.
B. the nuclear forces that hold nuclei together are
very short range
C. Both of these
D. Neither of these
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
If fusing H to He converts millions of tons of mass into
energy every second, why aren’t we worried about
using up the Sun?
A. The energy turns back into mass.
B. The proton-proton chain only operates for a few
seconds.
C. A million tons of mass is a tiny fraction of the total
mass of the Sun.
D. The Sun is constantly manufacturing new H to
replace the fused H.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The condition that keeps a Main-Sequence star
relatively stable in size and temperature is _____.
A. nuclear fusion
B. the Jeans Instability
C. hydrostatic equilibrium
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The Sun’s Luminosity comes primarily from_____.
A. chemical burning
B. gravitational contraction
C. nuclear fusion
D. nuclear fission
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Stellar Evolution and
“Death”
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
The Main Sequence isn’t Forever!
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Stars on the MS are stable/stationary
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Mass determines maximum core temperature & fate
Stars leave main sequence to become red giants or
supergiants
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
RED GIANTS & SUPERGIANTS
The Main Sequence isn’t Forever!
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Low & Moderate Mass Stars become red giants
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Up to about 4x Sun’s mass
Up to about type A
Max core temp supports fusion to He→C,O
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Core H Runs Out
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No more fusion in core.
What do you think
happens when the
power plant shuts
down?
He “ash”
core
Hint: think about
pressure & gravity
Image from: http://www.atnf.csiro.au/outreach/education/
senior/astrophysics/stellarevolution_mainsequence.html
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Core H Runs Out
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pressure reduces
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what happens when the
star shrinks?
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star begins to
collapse
He “ash”
core
It heats up!
Area around core
reaches 10,000 K
H fusion starts again
Astronomy 1 - Elementary Astronomy
Image from: http://www.atnf.csiro.au/outreach/education/
senior/astrophysics/stellarevolution_mainsequence.html
LA Mission College
Levine F2015
A Red Giant Emerges
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H fusion starts again—
Shell
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Causes outer layers to
expand
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When they expand,
they…..
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He
He fusing
“ash”
core
…cool
Red Giant
Core continues to heat
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at 100,000,000K He
begins fusing
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C & O build up
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
A Red Giant Emerges
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H fusing shell expands
He fusing shell forms
He fusing
core
Core stars to build up
C,O “ash”
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Life as a Red Giant (Low Mass Stars)
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Red Giant is
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MUCH larger
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Not as stable as a
MS star
cooler
more luminous
short-lived: about
1/10 Main
Sequence life
Astronomy 1 - Elementary Astronomy
Image from: http://www.fromquarkstoquasars.com/the-day-withno-tomorrow/
LA Mission College
Levine F2015
The Main Sequence isn’t Forever!
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High Mass Stars become red giants & Supergiants
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Above 4x Sun’s mass: OB and most A stars
Much less stable & predictable
Max core temp supports fusion up to Fe
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
High Mass Stars
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Starts like low mass
stars
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Red Giant/Supergiant
Core temps continue to
increase
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at ~1 billion K, C fusion
stars
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layers of fusion
up to Si (silicon)→ Fe
(iron)
Once Fe fusion starts,
death (supernova) is
imminent
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Let’s Practice
If the red giant phase lasts 10% of a stars life on the
main sequence, we would expect to find there are
A. more main sequence stars than red giants.
B. more red giants than main sequence stars.
C. the same number of red giants as main sequence
stars.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Why might we observe a larger fraction of red giants
compared to main sequence stars than the ~10% you
would expect from the previous question?
A. They live longer then main sequence stars.
B. They are larger and brighter than main sequence
stars.
C. They are closer to us on average than main
sequence stars.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
ENDGAME OF LOW MASS/AVERAGE STARS
STARS
From Red Giant to Planetary Nebula
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Low Mass Stars stop
core fusion with He
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H,He fusion shells
expand
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“Push off” outer
layers
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planetary nebula
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Planetary Nebulae
http://www.astro.washington.edu/users/balick/WFPC2/
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Final Remnant — White Dwarf
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Core exhausts He
Contracts & interior heats
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Contraction stopped by
electron degeneracy
pressure
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but not hot enough to fuse C
to O
resists putting 2 e in same
place
Core becomes white dwarf
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a hot, dense naked core
Artist’s concept
Image ESA/NASA
~25,000K at surface
up to 1.4 x Sun’s mass
compressed to Earth size
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
White Dwarf
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White dwarfs last a
long time
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Held up by e- pressure
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In isolation, very slowly
cool and fade away
Cannot shrink, cannot
heat up, cannot
increase pressure
“Stuck”
Astronomy 1 - Elementary Astronomy
Artist’s concept
Image ESA/NASA
LA Mission College
Levine F2015
Let’s Practice
A white dwarf is hot and tiny. This implies it will have a
_____ color and a _____ luminosity than its main
sequence progenitor.
A. redder, lower
B. redder, higher
C. bluer, lower
D. bluer, higher
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
ENDGAME OF HIGH MASS
STARS
Supernova Destroyer/Creater Space.com
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The biggah boomah
Artist’s Concept of Supernova
Credit: ESA
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Type II Supernova
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Huge cataclysmic explosion
about 10 billion times as luminous as the Sun
fade over months or years
everything heavier than iron fused by explosion
Leaves behind a neutron star or black hole
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Core-collapse
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"Onion layers" of heavier
and heavier elements in
their interiors.
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Fusion in stellar core
wont go heavier than
iron (Fe)
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Fusing Fe uses up
energy
Fe core reaches 1.4 M⊙◉☉.
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Chandrasekhar limit
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takes seconds!
electron degeneracy
pressure can’t hold it up
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Core-collapse
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The core collapses.
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Protons and electrons are
pushed together
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form neutrons and neutrinos
exert a tremendous outward
pressure.
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stops when neutrons getting
packed too tightly
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observe neutrino outburst
neutron degeneracy
outer layers fall inward
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outer layers crash into the
core and rebound
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shock waves move outward
Star explodes — Type II
Supernova
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
End result is either a Neutron Star or Black Hole
© NASA
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Depending on the.....?
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
End result is either a Neutron Star or Black Hole
© NASA
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Depending on the.....?
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Remaining mass in the core!
mass is (almost) everything if you are a star...
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The Neutron Star Route
• Collapsed core <2 or 3 M
⊙◉☉
• MS star about 8-20 M⊙◉☉
• made of degenerate
neutrons
• very intense magnetic
fields
• VERY Dense
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1.4 to 3 M⊙◉☉ compressed into
a radius of about 10 km.
As something spinning
collapses, it spins faster.
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Artist’s Concept of a Neutron star
undergoing a starquake. Credit: NASA
neutron stars spin very
fast
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Discovery of Neutron Stars/Pulsars
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Predicted in 1930s
discovered 1967
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A graduate student named Jocelyn Bell was monitoring radio emission from space
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discovered a really regular signal.
Unlikely anything natural could produce such a regular, repeating signal.
The source of the radio signals was dubbed "LGM1". (Little Green Men)
Several more were discovered.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Pulsars
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Astronomers finally
deduced that they were
observing very rapidly
rotating neutron stars -pulsars.
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Charged particles move
around the magnetic fields
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most intense around
the magnetic poles.
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As the pulsar rotates, acts
like a ”light house."
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When the radio emission
is pointed at us, we see a
"pulse."
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The Black hole Route
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Collapsed core >2 or 3
M⊙◉☉
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Progenitor star > about 20
M⊙◉☉
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for objects more massive
than a neutron star, there
is nothing that can stop the
inward collapse due to
gravity
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The final result is a black
hole, a very small, very
dense “singularity” that
warps spacetime
sufficiently that not even
light can escape.
Astronomy 1 - Elementary Astronomy
Artist’s Conceptof a Black Hole
Credit: NASA
LA Mission College
Levine F2015
SO WHAT IS A BLACK HOLE?
What is a black hole?
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Journey into a Black Hole
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
ANOTHER SCENARIO
(INVOLVING MORE THAN 1 STAR)
Type Ia Supernovae
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Ingredients : a white
dwarf with a post-mainsequence companion
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Or 2 white dwarfs
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companion dumps
material onto the white
dwarf
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When the mass > 1.4
Msun, the degenerate
gas cannot support the
pressure
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resulting supernova
completely obliterates
the white dwarf
Astronomy 1 - Elementary Astronomy
Artist’s Concept
Image: NASA/CXC/M Weiss.
LA Mission College
Levine F2015
Importance of Type Ia SN
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Standard Candle
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Can assume the same peak brightness is always produced
SNIa explosions happen under very consistent conditions
The light output of a Type Ia SN is therefore very
predictable
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Let’s Practice
What is the fate of a 10-solar mass star?
A. Type Ia supernova
B. Type II supernova
C. white dwarf
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
What is the fate of a 5 solar mass remnant core after a
Type II supernova has occurred?
A. neutron star
B. black hole
C. white dwarf
D. planetary nebula
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
If your black hole research spaceship approached the
site of very massive star that had gone supernova,
what would happen?
A. It would inevitably get sucked into the black hole
with no possibility of escape.
B. It would detect the gravitational pull of the black
hole and be able to go into orbit around it.
C. It would be unable to locate the black hole because
it’s, well, black.
D. It would be repelled by the black hole.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
WRAP-UP
Topic for Next Class
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Galaxies & Our galaxy
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Reading Assignment
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•
Astro:10&11
Astropedia:15&16
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Homework
•
HW SS Posted, Due 11/19
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015