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Title: ASTR 1120 General Astronomy: Stars


1
ASTR 1020 Introductory
Astronomy II Stars Galaxies
Week 16 (28April) Cosmology Cosmic microwave
background Hubble expansion, Dark energy Active
Galactic Nuclei (AGN) Life in the Universe
2
Hubble Expansion
Vkms H x DMpc H 71 km/s
Doppler Effect
3
Redshift (Doppler effect)expressed as z
  • Present day z 0
  • Furthest galaxy z 7-10
  • Cosmic Microwave Background z 1089
  • Big Bang z 8

4
The Hubble constant V H0 x D
H0 in km s-1 / Mpc (km / mega parsecs)
5
Use quasars as bright beacons see absorption
lines from intergalactic gas
6
Quasar spectra
Redshifted from emission lines Many
absorption lines (forest)
Lyman Alpha Forest
7
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8
Supernova Type Ia Evidence for Accelerating
Expansion
  • Two surveys agree
  • Distant supernovae appear too faint
  • More high-z data are needed

9
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10
  • Dark Energy
  • Type Ia supernovae
  • gt 1.4 Solar mass white dwarfs accreting
  • from companion
  • gt Standard candle!
  • gt Dimmer (farther) then expected from
    redshift
  • gt Expansion of Universe accelerating
  • (since 5 10 Billion years ago)
  • Cosmic Microwave Background
  • gt Standard Ruler!
  • gt Geometry of Universe is flat
  • gt Requires more than ordinary matter
    (4)

  • dark matter (26)
  • Dark energy tension in the vacuum!
    (70)
  • Matter dilutes dark energy is constant as
    volume grows

11
The History of our Universe
12
Summer Milky Way
Wei-Hao Wang
13
The Sky in Galactic Coordinates (projected)
14
Our Milky Way _at_ visual wavelengths
15
Our Milky Way _at_ near infrared wavelengths
16
Our Milky Way _at_ far infrared wavelengths
17
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18
Distant galaxies
1 Billion years ago distant galaxies _at_ near-IR
wavelengths
19
The Karl Jansky antenna in Holmdel, New Jersey
(1929) First detection of cosmic
radio waves
20
Discovery of Cosmic Microwave Background 1965
ATT Bell Laboratories, Crawford Hill, NJ
Bob Wilson Arno Penzias
21
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22
  • Note
  • Axes
  • Size of error bars (boxes)
  • Wiens law max frequency 160 GHz
  • Isotropic to 1/100,000!

23
Cosmic Microwave Background (CMB) Remove
constant background (2.728 K) Dipole
anisotropy Solar motion at 600 km/s
(Doppler shift) Remove dipole CMB
Galactic Plane
24
Cosmic Microwave Background (CMB) Remove
constant background (2.728 K) Dipole
anisotropy CMB Galactic Plane dust
Remove model of dust emission gt True
CMB
25
Wilkinson Microwave Anisotropy Probe
26
Wilkinson Microwave Anisotropy Probe (WMAP)
Insertion into Lunar Halo L2 orbit
27
Cosmic Microwave Background Snapshot of
3,000 K plasma when Universe was 380,000 yrs old
Redshifted by Expansion of the Universe x1,000
gt 3 K
28
Cosmic Microwave Background (WMAP 5 year map)
29
How does 1 side of the CMB know the temperature
and density on the other side of the sky - they
have never been in contact .. Or maybe they
have! gt Inflation
Alan Guth
30
The History of our Universe
31
Today lt Galaxies lt first stars
lt CMB ltBig Bang
32
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33
The Fate of the Universe
http//www-supernova.lbl.gov/
34
Composition of the Universe Ordinary Matter
(atoms, molecules, etc.) 4
Interacts with light, nuclear forces,
gravity Dark Matter
23 Does NOT
interact with light (its dark!) Interacts
with gravity Dark Energy
73
Does NOT interact with light (its dark!)
Tension in the vacuum Accelerates expansion
of the Universe
35
Dark Matter and the Fate of the Universe
  • Expansion begins with the Big Bang (well talk
    about this next week)
  • At that point, everything in the universe is
    flung apart at outrageous speeds!
  • Several different models for Past and Future
    depending upon the amount of dark matter

36
Predictions of General Theory of Relativity
  • Einstein in 1917 realized GTR predicted universes
    in motion, but preferred steady state added
    cosmological constant (CC) as repulsive force
    in space-time to counteract attractive force of
    gravity (A fudge factor!)
  • Willem de Sitter (A, Dutch, 1917) solves GTR
    equations with no CC and low density of matter
    showed universe must expand
  • Alexander Friedmann (M, Russian, 1920) solves GTR
    with no CC but any density of matter universes
    can expand forever, or collapse again, depending
    on mean matter density
  • Georges Lemaitre (P, Belgian, 1927) rediscovers
    Friedmann solutions, told Hubble (observing
    redshifts since 1924) that cosmic expansion
    suggests more distant galaxies should have
    greater redshifts (Hubble publishes V Hod in
    1929)
  • Einstein visited Hubble in 1932, said CC was the
    greatest blunder of his career

37
Very important diagram
  • Average distance between galaxies
  • 1 / expansion factor
  • 1 / (1 Z)
  • NOW is fixed in time (Z0)
  • Hubble constant NOW sets how fast universe is
    expanding NOW

OPEN
SIZE
FLAT
CLOSED
NOW
TIME
Big Bang when distance zero Z
infinity
38
The expansion rate of the universe is not
necessarily constant for all time
  • Just like a cannonball, GRAVITY should SLOW
    expansion rate ? deceleration
  • Different models for different amounts of dark
    matter
  • Lets ignore accelerating for now

39
Since gravity is what pulls everything back in,
there must be a magic number
  • Just the right amount of mass (in our current
    universe) to pull everything back together in an
    infinite amount of time
  • Just like our exact escape velocity for the
    cannonball
  • We call this exact amount of matter (spread out
    over the observable universe), the CRITICAL
    DENSITY
  • 10-29 grams/cm3 a few atoms in a closet

40
Critical Universe
  • Density of matter critical density
  • Will expand forever, but just barely

41
Recollapsing Universe
  • Dark matter density is greater than critical
    density
  • Expansion will stop in the future, will collapse
    back in
  • Big Crunch
  • Oscillations?

42
Coasting Universe
  • The universe has always expanded at the same rate
    (no deceleration due to gravity!)
  • The age of the Universe 1/Ho

43
Which model predicts the largest age for the
universe today?
Clicker Question
  • A. Recollapsing
  • (closed)
  • B. Critical
  • (flat)
  • C. Coasting
  • (open)
  • D. Accelerating

44
The Fate of the Universe
  • Hubble constant sets the expansion rate for NOW
  • Dark matter pulls expansion curves downwards
  • Upwards curve suggests DARK ENERGY pushing
    against gravity???!

45
The Birth of our universeAre
thereotherUniverses?
46
  • Some deep questions
  • What happened during the Big Bang?
  • What came before?
  • Is our universe the only one?
  • Are there other universes?
  • Why is the universe hospitable to life?
  • The anthropic principle
  • Are we alone?

47
  • Some Approaches
  • The Multiverse hypothesis
  • (L. Suskind hypothesis)
  • - A vast landscape of universes beyond our
  • horizon, each with variations in the
    constants
  • of nature.
  • - We can only exist in one suitable for us
  • Cosmic Evolution with Natural Selection
  • (Smolin/Harrison hypothesis)
  • - Black holes make Universes,
  • each with slightly different constants
  • - Universes that maximize number of
  • black holes are most successful
  • - Advanced life maximizes of black holes
  • gt Successful Universes have advanced
    life!
  • anthropic principle

48
Colliding Galaxies NGC 4676
Mice with HST Advanced Camera for Surveys
49
Stephans Quintet in HST detail
50
A mature exampleElliptical shape but with dust
lanes?
51
It may happen to us in future!
Andromeda (M31) in future
52
Messages From Galaxy Interactions
  • In dense clusters, galaxy collisions (grazing or
    even head-on) must have been common
  • With successive passages, spiral galaxies can
    tumble together to form a big elliptical
  • Vastly increased star birth from shocking the gas
    and dust (starburst galaxies coming up next!)
  • Start rapid feeding of supermassive black hole
    lurking at center of most galaxies (quasars
    coming up soon!)

53
M82 Starburst Result of interaction with M81
NGC3077
M82 - M81 - in visual
54
M82 Starburst interaction
NGC 3077
M 81
M 82
M82 - M81 - in 21 cm HI (radio)
55
M81/82 in Big Dipper UV
56
M82 in Big Dipper Hydrogen
57
Starburst Galaxies
M82 - visible
Chandra X-ray
  • Milky Way forms about 1 new star per year
  • Starburst galaxies form 100s of stars per year

58
Vigorous star birth The Antennae
HST detail NGC 4038/39
59
Starburst galaxies emit most of their light at
infrared wavlengths
  • Star formation heats dust to very hot
    temperatures
  • Hot dust glows strongly in the infrared
  • Much evidence for galactic fountains and giant
    supernova-driven galactic winds
  • Usually triggered by galaxy collisions or close
    passages of another galaxy

60
Active Galactic Nuclei Another Type of Galactic
Fireworks
  • Galaxies with strange stuff going on in their
    centers
  • Some galaxies at high redshift (large lookback
    times) have extremely active centers
  • More than 1000 times the light of the entire
    Milky Way combined from a point source at the
    center!!

61
Quasars
  • Quasi-Stellar Radio Source
  • Nuclei so bright (at nearly all wavelengths) that
    the rest of the galaxy is not easily seen
  • First discovered as radio sources - then found to
    have very high redshifts!

62
Sources of the radiation from bright nuclei in
active galaxies
  • Thermal radiation from a massive star cluster
  • Emission lines from hot gas
  • 21 cm from hydrogen gas
  • H-alpha from hydrogen gas
  • Synchrotron radiation from a black hole

63
Synchrotron
  • Synchrotron light is bright at both radio and
    X-ray wavelengths (far ends of the spectrum)

64
Whatever is powering these QSOs must be very
small!!
  • Some quasars can double their brightness within a
    few hours.
  • Therefore they cannot be larger than a few
    light-hours across (solar system size)
  • Why? Think about the time it takes light from the
    front of the object to get to us compared to the
    light from the back.

65
Quasar Central Engines
  • How do quasars emit so much light in so little
    space?
  •  
  • They are powered by accretion disks around
    supermassive black holes
  •  
  • In some quasars, huge jets of material are shot
    out at the poles. These jets are strong radio
    sources.

JET
DISK
66
Central Engine -- artists conception
  • Accretion disk around super-massive black hole
  • Inner parts of disk may or may not be obscured by
    dust
  • If bright nucleus is visible, looks like a
    quasar, if not, then its a radio galaxy

67
M87
68
M 87 Elliptical-galaxy In Virgo
cluster Active Galactic Nucleus
(AGN) Syncrotron jet from super-massive black
hole central
69
Prototypical radio galaxy
Giant elliptical galaxy NGC 5128 with dust
lane (from spiral galaxy?) Centaurus A
radio source (color lobes)
70
Cygnus A radio jets
400,000 ly
Jet as fine thread, big lobes at end, central hot
spot
VLA
71
Radio tails many shapes
NGC 1265 100K ly
3C 31 2 M light years
72
M87 elliptical with jet
800 km/s 60 ly away
  • Active galactic nucleus beams out very narrow jet
  • Accretion disk shows gas orbiting a 2.7 billion
    solar mass black hole first real proof !

73
Another example of central beaming engine
radio
active nucleus - HST
  • 400 light year wide disk of material in core of
    elliptical galaxy with radio jets looks like a
    supermassive black hole at work!

74
ASTR 1020 Introductory
Astronomy II Stars Galaxies
Week 16 (30April) Review Summary
75
The Universe
nearest star
planets
molecules
people
galaxies
quarks
atoms
nuclei
Universe
superstrings
stars
EM
weak
GUTS
gravity
strong
76
Forces in Nature
Strong Nuclear force
GUTS
Electromagnetic force
?
Electroweak force
Weak nuclear force
Gravity
energy
77
The Big Bang A graphic 14 billion year history
of the Universe
78
The first 3 minutes Making of the light
elements and isotopes
Observations show our Universe is here.
????????? critical Ordinary matter has
????0.04
79
Wilkinson Microwave Anisotropy Probe
1) Matter is evenly distributed on very large
scales in the universe
  • WMAP showed that the universe is, for the most
    part, isotropic (physically equal in all
    directions)
  • Variations in above image are at the .001 level!!

80
13 Billion years ago Cosmic structure
formation Dark matter halos collapsing gt
first stars
81
The Hubble Deep Field
Galaxies to z4!
82
What does the expansion of the universe most
accurately mean?
Clicker Question
  • Galaxies are moving apart through space
  • Space itself is expanding
  • Everything is expanding, including the earth, our
    bodies, etc
  • The Milky Way is at the center of the universe
    and all other galaxies are expanding away from us.

83
Making of a spiral galaxy
  • Start with a fairly uniform cloud of hydrogen
  • Gravitational collapse forms protogalactic clouds
  • First stars are born in this spheroid (such stars
    are billions of years old ? fossil record)

84
Small variant in spiral making
  • Several smaller protogalactic clouds may have
    merged to form a single large galaxy
  • May explain slight variations in stellar ages in
    the MW

85
Forming a disk with spiral
  • As more material collapses, angular momentum
    spins it into a disk
  • Stars now formed in dense spiral arms disk
    stars are younger!

86
Or now a different story.
  • Spiral galaxy collisions destroy disks, leave
    behind elliptical
  • Burst of star formation uses up all the gas
  • Leftovers train wreck
  • Ellipticals more common in dense galaxy clusters
  • So what?

NGC 4038/39 Antennae
87
Why are collisions between galaxies more likely
than between stars within a galaxy?
Clicker Question
  • Galaxies are much larger than stars
  • Galaxies travel through space much faster than
    stars
  • Relative to their sizes, galaxies are closer
    together than stars
  • Galaxies have higher redshifts than stars

88
Quasars
REVIEW
  • Quasi-Stellar Radio Source
  • Nuclei so bright (at nearly all wavelengths) that
    the rest of the galaxy is not easily seen
  • First discovered as radio sources - then found to
    have very high redshifts!

89
Do ALL galaxies have supermassive black holes?
  • probably YES!
  • Part of normal galaxy formation?
  • More quasars seen in the distant (early) universe
    than now
  • Black holes gradually grow, but can run out of
    available fuel and become nearly invisible (like
    in our Milky Way)

90
Somehow, the rest of the galaxy knows about the
SMBH during formation!!
91
Resurrected by galaxy collisions?
  • Many galaxies with bright nuclei show signs of
    being disturbed
  • Collisions funnel material down into the black
    hole lurking at the core
  • Expect more such collisions in denser early
    universe
  • This may help explain why fewer quasars today

92
Quasars reveal Protogalactic Clouds
  • Looking for gas between the galaxies
  • Cold, invisible, too dim even at 21 cm
  • But quasars provide the way to detect them!

Simulation of universe
93
Now on to Case for Dark Matter Chapter 22
  • gt 90 of mass of universe is dark matter
    (invisible, missing matter)
  • Detectable ONLY via its gravitational forces on
    luminous matter (gas and stars)
  • Note -- this dark matter is NOT the same as black
    holes, brown/black dwarfs, or dust

94
Formation of Structure
  • In the beginning
  • Density distribution mostly smooth but very small
    ripples exist in density
  • Gravity pulls together dark matter in slightly
    denser regions to form dark halos
  • Light matter radiates energy and sinks to the
    middle to form galaxies

95
WMAP
  • WMAP showed that space was relatively isotropic
    (physically similar) but different at the .001
    level

96
If the Universe was mostly smooth, how did those
lumps turn into galaxies?
  • Simulations show that gravity of dark matter
    pulls mass into denser regions universe grows
    lumpier with time
  • Those lumps are galaxy clusters

97
  • Observations of galaxy positions reveal extremely
    large structures clusters, superclusters,
    walls, voids

98
vs
Computer simulations
Real data
  • Agreement is generally pretty good!
  • Despite the fact that we dont know what the CDM
    is!

99
Lessons from Imaginary Universes
  • Cold (Slow) dark matter works better than hot
    (fast) dark matter
  • Neutrinos are too fast structure would be
    smeared out
  • What is slow and dark enough? We dont know yet!
  • Particle experiments under way..

100
Star Formation
Shrink size by 107 increase density by x 1021 !
Where planets also form
  • Giant Molecular Cloud Core

Raw material for star birth
  • Gravitational Collapse Fragmentation

Proto-stars, proto-binaries, proto-clusters
  • Rotation Magnetic Fields

Accretion disks, jets, outflows
  • Planets

Most may form in clusters!
C. Lada
101
Orion Molecular Clouds 13
Orion B
2.6 mm
CO
Orion Nebula
Orion A
102
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103
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104
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105
Young Proto-planetary Disk
106
Class I Outflow HH 46/47
Ha SII OII
107
Class I Outflow HH 46/47
Spitzer IRAC
3 8 mm
108
  • Evolution of
  • A Star
  • Birth
  • Main-sequence
  • life
  • - fusion HgtHe
  • Death
  • gt 60 M
  • black hole
  • 8 60 M
  • neutron star
  • lt 8 M
  • white dwarf

The Sun .
109
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