ASTR 1120 General Astronomy: Stars

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ASTR 1020 Introductory
Astronomy II Stars Galaxies
Week 15 (23April) Cosmology Hubble
expansion Abundance of the elements Dark matter,
dark energy
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Measuring big distances to galaxies

• STANDARD CANDLES -- important ones in
  distance ladder, or chain
• 1. Main-sequence fitting
• 2. Cepheid variables
• 3. Tully-Fisher relation
• 4. White dwarf supernovae

Brightness Luminosity / (Distance)2

• 5. Hubble Expansion of the cosmos

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The Cosmological Principle
The universe looks about the same no matter where
you are within it

• Matter is evenly distributed on very large scales
  in the universe
• No center
• Not proven but consistent with all observations
  to date

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Cosmology the Universe

• Hubble Expansion the stretching of space
• Velocity 71 (km/s per Mpc) x
  Distance
• Pattern of cosmic abundances of the elements (by
  mass).
• Hydrogen 70 - Only element to
  emerge from
• Big
  Bang
• Helium 28 - Thermonuclear
  fusion (H gt He)
• in
  1st 3 minutes!
• C, N, O, Si, Fe, etc. - Formed in
  stars.
• The Cosmic Microwave Background
• Picture of the Universe at Age 380,000
  years
• T 2.73 K (?peak 1 mm gt f 300
  GHz)
• Smooth to 1 part in 100,000

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Composition of the Universe
Ordinary Matter (atoms, molecules, etc.)
4 Interacts with light, nuclear forces,
gravity Dark Matter
26 Does NOT
interact with light (its dark!) Interacts
with gravity Dark Energy
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Does NOT interact with light (its dark!)
Tension in the vacuum Accelerates expansion
of the Universe
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Cosmic abundances
Big Bang Stars
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Big Bang Nucleosynthesis p-p chain Hgt He
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Big Bang Nucleosynthesis Abundances vs.Current
density
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Big Bang Nucleosynthesis Abundances
vs. Current density
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Spiral galaxy ROTATION CURVES

• Discovered by Vera Rubin in the 1970s
• Highly controversial until many rotation curves
  confirmed

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Nearly all galaxies show these same rotation
curves

• Flat rotation curve of a galaxy reveals
• High speeds far from luminous center
• indicates large amounts of matter in the outer
  regions
• Dark Matter

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Individual galaxies have huge amounts of dark
matter

• Rotation curves motions of stars in the galaxy
• Reveal that dark matter extends beyond visible
  part of the galaxy, mass is 10x stars and gas

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Galaxy Clusters revealdark matter

• 1 Galaxy velocities too large to be explained
  by gravity of visible galaxies
• Expected 100 km/sec for a typical cluster, found
  1000 km/sec!
• Discovered in 1930s by Fritz Zwicky (they didnt
  believe him, either)

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2 Hot x-ray emitting gas in cluster

• Gas between galaxies is also moving because of
  gravity of dark matter gets very hot
• 1000 km/sec ? 100 million K emits X-rays!

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3 Gravitational Lenses

• Dark ( luminous) matter warps space
• acts like a lens and distorts and magnifies the
  view of more distant galaxies
• Lens properties reveal how much mass is contained
  (in total, both luminous and dark) in the cluster

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Gravitational lensing how it works
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Gravitational lensing can make a variety of shapes
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Gravitational lensing by a hypothetical miniature
black hole
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Single galaxies can act as lenses too!
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Compared to a low-mass cluster, how will the
lensed images of background galaxy that has been
lensed by a high-mass cluster look?
Clicker Question

• The images will be closer together
• The images will be further apart
• There will be no change in the position of the
  images

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Two galaxy clusters are studied. Cluster A has
typical velocities for its galaxies of 300
km/sec, Cluster B has 1000 km/sec. Which is most
likely?
Clicker Question

• Cluster A has more galaxies than cluster B
• Cluster A is more massive than cluster B
• Gas between galaxies in cluster A will have lower
  temperature than gas in cluster B
• Cluster B galaxies are more likely to be spirals

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• C. Lower velocities in Cluster A mean that there
  is less mass overall in that cluster. This
  probably means fewer galaxies. Less mass also
  means a cooler intracluster gas temperature

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How much dark matter overall?

• All cluster methods generally agree (yay!)
• Overall, about 10 times as much dark matter as
  normal matter in the universe
• Note Our solar system has much more light matter
  than dark matter here! (DM probably immeasurable.)

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What is dark matter?

• Two leading contenders
• Possibility 1 MACHOs
• MAssive Compact Halo Objects
• This IS stuff weve studied already very faint,
  normal things baryonic matter (atoms, protons,
  neutrons)
• Brown dwarfs, black holes, black dwarfs, cold
  neutron stars, etc
• Could be floating through galaxy halos unnoticed

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MACHO Searches

• Use gravitational lensing
• When a MACHO passes directly in front of a star,
  that star suddenly brightens!
• Focusing effect of a compact massive object

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MACHO hunt results

• MACHOs have been reliably detected since 1997 by
  looking at the LMC
• One team looked at nearly 12 million stars (over
  6 years) and discovered 13-17 MACHOs
• Not nearly enough to account for all the
  missing mass

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Possibility 2 WIMPs
Weakly Interacting Massive Particles

• Non-baryonic matter? subatomic particles
• Neutrinos? Probably not. They move too fast and
  cant be collected into stable galaxy halos
• Other particles???
• Leftover material from the Big Bang
• Slower particles Cold Dark Matter

Unknown particles!!
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Both our past and our future depend on dark matter

• Past Birth of galaxies and clusters
• Dark matter provided the first tugs to assemble
  galaxies and clusters out of protogalactic clouds
• Future Fate of the universe
• Is there enough matter in the universe (both
  light and dark) to reverse the expansion and pull
  the universe back together again?

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• Dark Matter
• Ordinary matter traced by light
• (X-rays, UV, light, IR, radio)
• gt Ordinary matter (stars, gas, dust)
• Gravitational lensing (trace ALL matter
• ordinary dark)
• gt gravity implies 5 X more matter than we
  see!
• gt Its dark - does NOT interact with light or
• nuclear forces. Can only be detected
• by its gravity.
• What is it? Weakly interacting massive
  particles?
• Super-symmetric partners?

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Galaxies Dark matter

• Review galaxy morphology, properties, types
• Galaxy clusters motions gt 5x more mass than
• in stars and gas gt Dark matter
• Rotation curves gt Dark matter
• cold dark matter (CDM) vs. hot dark
  matter(HDM)
• cold gt V lt 300 km/s hot V gt 300 km/s
  to C
• MACHOs (Massive Compact Halo Objects)
• black holes, neutron stars, brow dwarfs,
  rocks
• vs.
• WIMPs (Weakly Interacting Massive Particles)
• exotic sub-atomic particles (photinos,
  axions, )

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Balloon analogy for expanding universe

• On an expanding balloon, no galaxy is at the
  center of expansion no edge
• Expansion happens into a higher dimension (2-D
  surface into a 3-D space)

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V H x D The only possible
law that has not Center of the Universe!
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the Expanding Universe

• NOT like an explosion of galaxies THROUGH space
  from a center place
• The space BETWEEN galaxies is expanding, carrying
  the galaxies way from each other
• Why dont galaxies themselves expand? Gravity!

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Redshift (Doppler effect)expressed as z

• Present day z 0
• Furthest galaxy z 7-10
• Cosmic Microwave Background z 1089
• Big Bang z 8

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Supernova Type Ia Evidence for Accelerating
Expansion

• Two surveys agree
• Distant supernovae appear too faint
• More high-z data are needed

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• 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

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

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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
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Cosmic Microwave Background (CMB) Remove
constant background (2.728 K) Dipole
anisotropy CMB Galactic Plane dust
Remove model of dust emission gt True
CMB
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Wilkinson Microwave Anisotropy Probe
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Wilkinson Microwave Anisotropy Probe (WMAP)
Insertion into Lunar Halo L2 orbit
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Cosmic Microwave Background (WMAP 5 year map)
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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
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The History of our Universe
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Today lt Galaxies lt first stars
lt CMB ltBig Bang
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The Fate of the Universe
http//www-supernova.lbl.gov/
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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
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Does NOT interact with light (its dark!)
Tension in the vacuum Accelerates expansion
of the Universe
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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

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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

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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
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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

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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

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Critical Universe

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

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Recollapsing Universe

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

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Coasting Universe

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

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Which model predicts the largest age for the
universe today?
Clicker Question

• A. Recollapsing
• (closed)
• B. Critical
• (flat)
• C. Coasting
• (open)
• D. Accelerating

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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???!

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The Birth of our universeAre
thereotherUniverses?
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• 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?

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• Some Approaches
• The Multiverse 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

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Making ellipticals

• Higher density much faster star formation uses
  up all the gas
• Nothing left to make a disk
• or
• Lower spin
• Gas used up before angular momentum took over
• Now we see a sphere of old stars

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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
  (centers of clusters contain central dominant
  galaxies)
• So what?

NGC 4038/39 Antennae
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Colliding Galaxies NGC 4676
Mice with HST Advanced Camera for Surveys
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Stephans Quintet in HST detail
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A mature exampleElliptical shape but with dust
lanes?
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It may happen to us in future!
Andromeda (M31) in future
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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!)

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M81/82 in Big Dipper UV
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M82 in Big Dipper Hydrogen
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Starburst Galaxies
M82 - visible
Chandra X-ray

• Milky Way forms about 1 new star per year
• Starburst galaxies form 100s of stars per year

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M82 Starburst Result of interaction with M81
NGC3077
M82 - M81 - in visual
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M82 Starburst interaction
NGC 3077
M 81
M 82
M82 - M81 - in 21 cm HI (radio)
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Vigorous star birth The Antennae
HST detail NGC 4038/39
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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

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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!!

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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!

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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

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Synchrotron

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

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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.

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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
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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

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M87
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M 87 Elliptical-galaxy In Virgo
cluster Active Galactic Nucleus
(AGN) Syncrotron jet from super-massive black
hole central
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Prototypical radio galaxy
Giant elliptical galaxy NGC 5128 with dust
lane (from spiral galaxy?) Centaurus A
radio source (color lobes)
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Cygnus A radio jets
400,000 ly
Jet as fine thread, big lobes at end, central hot
spot
VLA
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Radio tails many shapes
NGC 1265 100K ly
3C 31 2 M light years
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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 !

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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!

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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!!

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Distance (in an expanding universe)

• Say it takes 400 million years for light to get
  from galaxy A to us in Milky Way
• Yet during travel in spacetime, both A and MW
  have changed positions by expansion
• Thus distance is a fuzzy concept LOOKBACK
  TIME is more accurate

TIME
A
MW
DISTANCE
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Since the universe is expanding, light traveling
through the universe feels the stretch as it
travels

• Cosmological Redshift

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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.

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Chapter 21 Galaxy Evolution

• Observing galaxies at different redshifts
  (lookback times)
• ?
• Allows us to assemble a sequence of galaxies
  showing birth and evolution
• ?
• Check via computer models of gas, gravity and
  star formation

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The Hubble Deep Field
Galaxies to z4!
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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)

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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

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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!

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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
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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

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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!

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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)

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Somehow, the rest of the galaxy knows about the
SMBH during formation!!
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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

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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
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Use quasars as bright beacons see absorption
lines from intergalactic gas
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Quasar spectra
Redshifted from emission lines Many
absorption lines (forest)
Lyman Alpha Forest
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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

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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

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WMAP

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

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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

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

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vs
Computer simulations
Real data

• Agreement is generally pretty good!
• Despite the fact that we dont know what the CDM
  is!

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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..

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