Download Galaxies Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015

Galaxies
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
Quotes & Cartoon of the Day
“The great spirals...
apparently lie outside our
stellar system.”
Copyright © 2012 by Sidney Harris.
-- Edwin Powell Hubble
“Theories crumble, but good
observations never fade.”
-- Harlow Shapley
“Is it not careless to become
too local when there are four
hundred billion stars in our
galaxy alone.”
-- A. R. Ammons
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Announcements
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SS Homework due 11/19
3rd midterm 12/3
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I will drop the lowest midterm grade
Minor schedule update posted
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Last Class
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Stellar Evolution ctd.
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Red Giants and Supergiants
Endgame
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Low mass stars— planetary nebulae, white dwarfs
High mass stars — supernovae, neutron stars, black holes
Binaries & Clusters (time permitting)
Galaxies
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What’s a Galaxy?
Galaxy types
LT Galaxy classification
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
This Class
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Stellar Evolution wrapup.
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Binaries & Clusters
Galaxies
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Black holes
What’s a Galaxy?
Galaxy types
LT Galaxy Classification
Our Galaxy, the Milky Way
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
JOURNEY INTO A BLACK HOLE
Journey into a Black Hole
Astronomy 1 - Elementary Astronomy
LA Mission College
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ANOTHER SCENARIO
(INVOLVING MORE THAN 1 STAR)
Type Ia Supernovae
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Ingredients : a white
dwarf & a post-mainsequence companion
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companion dumps
material onto the white
dwarf
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Mass reaches 1.4 M☉
electron degeneracy
can’t support star
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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SNIa are Standard Candles
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very consistent conditions
light output very predictable
always have same peak luminosity
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
Stars in Groups
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
Binaries & Clusters
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Single stars are not common!
1/2-2/3 stars are in pairs (binaries) or larger
multiple star systems
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
BINARY STARS & MULTIPLE
STAR SYSTEMS
Binary Stars
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2 stars orbiting
around their common
center of mass
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Important
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masses of component
stars can be
determined from orbit
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other properties can be
indirectly estimated
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e.g. radius and density
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Mass Transfer
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If stars are close, gravity tidally distorts outermost
layers
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can exchange mass
can lead to novae & type Ia supernovae
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Let’s Practice
Suppose you discover two stars that appear to be very
close to each other in terms of angular separation.
You measure the stellar parallax for each and find one
to be at 4 pc and the other at 10 pc. Have you
discovered a binary star system?
A. Yes
B. No
C. Maybe
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
HDE 226868, a very high mass star, orbits Cygnus X-1,
the first widely accepted black hole. The fact that
Cygnus X-1 was in a binary system was key in making
the initial argument that it was a black hole. This was
because _____.
(use your knowledge of binaries and black holes to
reason this out)
A. HDE 226868 was observed falling into Cygnus X-1
B. the light from HDE226868 illuminates Cygnus X-1
allowing it to be seen
C. the orbit of HDE226868 allows the mass of
Cygnus X-1 to be determined
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
CLUSTERS
Stars in Groups: Clusters
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Stars come in singles & binaries but also in larger
groups. Clusters of stars are groups of stars that
formed at the same time, from the same molecular
cloud.
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similar age
similar metallicity
Cluster HR diagrams change as the cluster ages
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Stars in Groups: Clusters
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Open Clusters
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Sparse & small
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Loosely grouped & move
through space together but
can be disrupted
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Usually only a few hundred to
a few thousand stars
“Young” subsequent
generation metal-rich
stars
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Appear bluer (Population I)
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Stars in Groups: Clusters
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Globular Clusters
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Spherical collection of
stars gravitationally
bound together
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dense
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hundreds of thousands to
millions of stars, packed most
densely in the center.
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Orbit the galactic core in
the halo (not in the
plane of the galaxy)
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“Old” first generation
metal-poor stars
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Appear redder (Population II)
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Let’s Practice
In a stellar cluster, all the members have ______.
A. the same spectral type
B. similar age
C. Both
D. Neither
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
You observe two similar star clusters, which you call
Wally and Eddie. You collect enough data on each
cluster to plot its H-R diagram. The brightest main
sequence star in Wally is almost 10 times brighter than
than the brightest main sequence star in Eddie. What
do you conclude?
A. Wally is larger than Eddie
B. Eddie is larger than Wally
C. Eddie is younger than Wally
D. Wally is younger than Eddie
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The Interstellar Medium
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
The Interstellar Medium (ISM)
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material which fills space between stars
approximately 15% of the visible matter in the Milky Way is ISM
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Mostly Hydrogen and Helium (99%)
small fraction dust/PAHs
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nebulae
polycyclic aromatic hydrocarbons
trace amounts of many other compounds
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
ISM
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75% H, 25% as He.
average density ~1 atom per
cc
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air
~30,000,000,000,000,000,000
molecules per ccc
Molecular Clouds
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Orion Nebula — emission
Cold clouds of neutral atomic
or molecular gas & dust
Horsehead Nebula, dark
Witch Head Nebula
— reflection
dark nebulae
reflection nebulae (blue)
HII regions
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Hot ionized hydrogen
bright, usually pink emission
nebulae
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Galaxies: Classification,
Spiral Structure, Oddballs
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
What is a galaxy?
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large-scale collections
of stars, gas, and dust
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galaxies & intergalactic
medium make up the
universe
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held together by
gravity
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organized around a
galactic nucleus
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elliptical or spiral in
shape
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small % irregular
Astronomy 1 - Elementary Astronomy
A Distant Cluster of Galaxies
Image Credit: FORS1, 8.2-meter VLT, ESO
LA Mission College
Levine F2015
Galaxies come in many shapes & sizes
Credit: NASA; ESA; G. Illingworth, D. Magee, and P. Oesch, University of California, Santa Cruz; R. Bouwens, Leiden
University; and the HUDF09 Team
Hubble eXtreme Deep Field (XDF) showing 5500 galaxies
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
DISCOVERY OF GALAXIES
IN WHICH OUR WORLD BECAME SMALLER
ANOTHER TIME
Galaxies
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Until early 20th century
thought to be “spiral
nebulae”
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By 1920 some
scientists began to
argue they might be
“island universes”
outside our own system
M51 -- the Whirlpool galaxy
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Edwin Hubble
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1920 so-called Great
Debate
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Shapley-Curtis debate
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Heber Curtis — spiral
“nebulae” are external
galaxies
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no “winner”
Harlow Shapley —
universe is 1 galaxy, spiral
nebulae are mostly gas
Edwin Hubble
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final “proof"
1923-26
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Edwin Hubble
Image Credit: Caltech
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Used new 100” telescope on Mount Wilson
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observed individual stars in in M31 (the Andromeda Galaxy)
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identified Cephied variable stars which gave a distance
to M31 well outside the Milky Way
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also developed the currently used system of galaxy
classification & discovered Hubble’s Law
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
GALAXY CLASSIFICATION
Three main types
Whirlpool Galaxy (M51)
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Spirals
NASA and European Space Agency
NGC 1132
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Ellipticals
Large Magellenic Cloud
NASA, ESA, and the Hubble
Heritage Collaboration
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Irregulars
Eckhard Slawik
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Morphological Classification Scheme
NASA/ESA
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Elliptical Galaxies
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Elllipsoidal shape &
smooth brightness
profile
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~20% of observed
galaxies
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10s of millions to > 1
trillion stars
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older, red, low-mass
stars
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sparse interstellar
medium
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minimal star formation
activity
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Spirals
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Round bulge, flat
disk, spiral arms and
spherical halo
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Divided into “normal”
(S) and “barred” (SB)
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Spirals
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together make 77% of
observed galaxies
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Younger blue stars in
arms
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Older red stars in
bulge and halo
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Sa
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Sb
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Sc
M99
NOAO/AURA/NSF
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
SBa
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
SBb
NGC 1365 APOD Nov 24 2012
SN2012fr
discovered 10/27/12 type Ia supernova
-- explosion of a
white dwarf star.
Image Credit & Copyright: Martin Pugh
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
SBc
NGC 7479
ESA/Hubble & NASA
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Irregular Galaxies
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Denoted Irr
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about 3% of
observed
galaxies
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Mostly
young, blue
stars
Lack
symmetry
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
WARM-UP QUESTION
A galaxy that appears to be populated by mostly red
stars, likely _____.
A. never had blue stars in the galaxy.
B. had blue stars that are not present anymore but
were at one time long ago.
C. has been around long enough for blue stars to all
evolve into the red main sequence stars we see.
D. never contained enough gas to have blue stars
develop.
E. as blue stars that are being blocked by dust.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
LT GALAXY CLASSIFICATION
A galaxy that appears to be populated by mostly red
stars, likely _____.
A. never had blue stars in the galaxy.
B. had blue stars that are not present anymore but
were at one time long ago.
C. has been around long enough for blue stars to all
evolve into the red main sequence stars we see.
D. never contained enough gas to have blue stars
develop.
E. as blue stars that are being blocked by dust.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Let’s Practice
How would you classify
the Milky Way?
NASA/JPL-Caltech/R. Hurt
A. SBbc
B. Sb
C. S0
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The centers of most spiral galaxies appear redder than
the arms. The most likely explanation for this is _____.
A. young blue stars are primarily in the arms and old
red stars in the bulge
B. nuclear reactions in the center are creating heat
C. the black hole in the center is glowing red
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Elliptical galaxies contain mostly red stars. What can
you conclude about the rate of star formation in
elliptical galaxies?
A. Few to no new stars are forming.
B. Many new stars are forming.
C. There is not enough information to conclude
anything.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
THE PUZZLE OF SPIRAL
STRUCTURE AND ITS SOLUTION
The Winding Dilemma
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1925 Bertil Lindblad
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stars can not stay
arranged in a spiral
shape
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arms “wind up”
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implies few spiral
galaxies
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but we see many
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Lindblad proposed
spiral structure
actually regions of
increased density
the “winding
dilemma”
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Density Waves
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Therefore something other than a fixed pattern of
stars must account for spiral shape
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The stars must move THROUGH the pattern
Think of a traffic jam
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Density Wave in a Galaxy
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Lin & Shu (1965)
developed a plausible
spiral density wave
theory
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The stars and gas
move through the
spiral structure
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Gas is compressed and
star formation is
triggered
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Slightly Silly Video
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
We live in a Galaxy:
The Milky Way
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
INTRO TO THE MILKY WAY
The Milky Way
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Our home galaxy
A barred spiral galaxy
From our solar system, we see this...
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Milky Way over the VLT
Image Credit: ESO (Yuri Beletsky)
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Structure of the Milky Way
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Looking through the disk from inside and combining the
2-D data with distance information allows us to construct
a model of what the Milky Way looks like from outside...
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Edge-on Model
http://woodahl.physics.iupui.edu/Astro105/
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Face-on Model
Image Credit NASA/JPL-Caltech/R. Hurt
Astronomy 1 - Elementary Astronomy
LA Mission
College
Image Credit
NASA/JPL-Caltech/R.
Hurt
Levine F2015
Structure of the Milky Way
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Bulge: spherioidal
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about 6000 ly diameter
Densely packed old red stars
Bar
Disk: flat
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about 90,000 ly x 900 ly
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Sun about 24,000 ly from center
Stars and interstellar gas and
dust, including young stars
Halo: Spheroidal
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about 300,000 ly diameter
Image Credit: R.J. Hall
old stars, globular clusters, dark
matter, hot gas
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
3D Model
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
WHAT’S IN THE MW?
Milky Way Recipe
300 ± 100 billion stars
at least 1983 planets
Interstellar Medium (ISM) ~ 1010 M⊙◉☉ Supermassive Black Hole ~ 4-4.5 x 106 M⊙◉☉ Dark Matter
to account for a total mass of 1-1.5 x 1012 M⊙◉☉
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Where is the Interstellar Medium?
Milky Way Galaxy
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Interstellar Medium =
ISM
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Everywhere between
stars
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not uniformly
distributed, denser in
bar and arms
Image Credit NASA/JPL-Caltech/R. Hurt
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
THE GALACTIC CENTER
The Galactic Center
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Images about 8° across. GC in upper left
Entirely obscured in visible light
First explored using radio astronomy
later further explored with IR astronomy
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The Galactic Center
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The GC is very wierd
place
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WAAAY down inside
the bulge
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This image about 3°
(1400 ly) across
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Sgr A* location of
black hole
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Supermassive BH in MW
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
The Galactic Center
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stellar orbits in the
central 3 ly
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evidence for a
supermassive black
hole, with mass 4
million times the
mass of the Sun.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
DARK MATTER
•The
data (blue curve) indicate the stars in the
outer Galaxy have higher orbital speeds than
can be explained by the known mass. •Dark
matter that extends to great distances
from the galactic center provides the
gravitational force needed to give the outer
stars these higher speeds.
Predicted Keplerian orbit
based on cataloged content
Actual rotation of Milky Way
Astronomy
1 - Elementary Astronomy
LA Mission College
Levine F2015
http://www.astro.ufl.edu/~guzman/ast1002/class_notes/Ch15/gal_rotation.gif
What is Dark Matter?
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Rotation curve provides evidence mass
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But we don’t see it as stars, dust, gas
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We call it dark matter because we haven’t directly
detected it through observing light
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We don’t really know what it is made out of, we just know
where it is and how much of it there is!
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In the Milky Way, most is in the halo, and possibly an
extended disk
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6 x1011 to 3 x 1012 M⊙◉☉
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
WRAP-UP
Topic for Next Class
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Hubble’s Law & the Expansion of the Universe
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
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HW SS Due
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015