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Evidence for the Big Bang

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Isotropy & Homogeneity (6) The Universe is Isotropic. Nearby, the universe is highly anisotropic ... million galaxies; approaching isotropy. 3-D locations. 10, ... – PowerPoint PPT presentation

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Title: Evidence for the Big Bang


1
Evidence for the Big Bang
  • Ages of the oldest cosmic objects ? converge on
    15 Gyr
  • Cosmic Expansion ? began 15 Gyr ago
  • Distant universe looks different ? Extreme youth
    15Gyr
  • Cosmic Microwave Background ? Seeing early
    fireball
  • 24 Helium abundance everywhere ? made in v. hot
    BB

2
1. Cosmic Ages
3
Star Cluster H-R Diagrams
  • Cluster stars have same age but range of mass
  • Main Sequence Turn Off ? age of cluster
  • Oldest (globular) clusters are 10-15 Gyr old

Globular Cluster M55
4
Young-ish Cluster
Old Cluster
5
Star Cluster H-R Diagrams
6
Older stars are less polluted
7
Cosmic Expansion the Hubble Law
8
(5) The Hubble Law
  • 1910 1915 Slipher most galaxies show Doppler
    redshifts
  • 1930 Hubble found V H d H Hubbles
    constant
  • H 75 5 km/s/Mpc (for V in km/s d in Mpc)

Nearby Galaxies Cepheid distances
Hubble
Many Galaxies various methods
9
View from galaxy A
B
A
10
View from galaxy B
B
A
11
Consequences of the Hubble Law
The fact that V d has some fascinating
consequences
  • Everyone sees the same expansion !
  • Cosmological Principle (deeply egalitarian)
  • There is no central location !
  • or. everywhere feels central to the expansion
  • (we will discuss the question of edges later)
  • Future Universe ? emptier lonely
  • Past Universe ? more crowded ? v.
    different
  • Everything together at particular time ? Big
    Bang !

12
Age of the Universe
When did the Big Bang happen ? Easy use V Ho
d
  • Assume expansion velocities have been
    constant
  • ? time to reach d moving at V is tstart
    d / V
  • Hubble law gives d V / Ho
  • ? tstart V / Ho / V 1/Ho
  • ? Age of Universe inverse of the Hubble
    constant !
  • (how long does it take to travel 1Mpc moving
    at 70 km/s)

1.39 1010 years 13.9 Gyr (13.7 with
change in V) (Universe is 3
older than the Earth/Solar system)
13
Redshift
Cake-mix (space) expands Carries raisins
(galaxies) along Raisin speeds obey Hubble law
Light stretched as it crosses expanding space.
?obs / ?em Sizenow / Sizethen Astronomers
use z ?? / ?em so Sizenow / Sizethen 1
z
14
3. The Youthful Distant Universe
15
(10) Galaxy Construction
  • Look very far ? long ago e.g. HDF
  • see to 1.5 Gyr ABB (adolescents, not infants)

Irregular (e.g. LMC)
  • Many smaller galaxies, resemble irregulars
  • Not yet mature no spirals/ellipticals

Small pre-galactic clumps merge to make bigger
galaxies hierarchical assembly small ?
bigger ? big ? huge
16
Galaxy mergers more common in the past
17
(10b) Star Formation History
  • Galaxy building blocks appear blue/distorted/inte
    racting
  • ? interactions common (Universe much smaller)
  • ? mergers trigger high star formation rate
  • ? Universes youth more dramatic relatively
    quiet today

18
(10c) Universe at 1 Gyr
  • Spectacular sight proto-galaxies merging,
    everything closer,
  • huge HII regions, OB stars common, SN common

Cosmic history like fireworks display in
reverse Grand finale occurs first
Artists view of galaxy youth
19
Quasars more common in the past
20
First evidence for evolving Universe
21
4. The Cosmic Microwave Background
22
(7) Cosmic Microwave Background
  • Look very far away ? very long ago ? see Big Bang
    !!
  • Direction ? Everywhere the whole sky !!
  • Spectrum ? Microwaves red-shifted flash !!

What we see
Universe at Big Bang
Universe today
23
(7e) CMB Image
  • Exceedingly uniform,
  • with two contaminants
  • 1) dipole MW moving _at_
  • 540 km/s towards Virgo
  • 2) MW plane contamination
  • Remove these to reveal
  • Highly uniform ? no stars
  • or galaxies diffuse hot gas
  • Very slight patchiness
  • 10-5 variations sound
  • waves grow into galaxies

Rotate
Flyby
24
5. Helium Deuterium Synthesis
25
(12) Early Times (tlt10 min) Helium synthesis
star core ! Expect nuclear reactions
b) Calculations show p n ? He4 ( )
26
(12b) Cosmic Nucleosynthesis details
Cosmic thermal history 1010 yr (3K) now, 3K
109 yr (30K) first galaxies 108 yr (300K)
first stars 4105 yr (3000K) fog clears 5104 yr
(104K) ?rad ?matter 1 3 min (109K) fusion
allowed range 4
27
The Cosmological Principleimplies Isotropy
Homogeneity
28
(6) The Universe is Isotropic
Nearby, the universe is highly anisotropic On
large (gt100 M-ly) scales, it is highly isotropic
Two pictures of 31,000 distant radio
galaxies (typically, 2-5 G-ly)
29
Deep Galaxy Quasar Surveys
30
2 million galaxies approaching isotropy
31
3-D locations
200,000 galaxies out to 2 G-ly
10,000 quasars out to 14 G-ly evolution now
visible
32
Dark Matter
33
(7) Galaxy Rotation Dark Matter
  • Use Doppler shifts to measure rotation curves
  • similar to MW ? rapid rise, flat out beyond
    galaxy edge
  • ? dark matter halo Mhalo 10 Mstars
  • nature unknown, probably WIMPs (like heavy
    neutrinos)
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