Observational Cosmology Jonathan P. Gardner NASA’s Goddard Space Flight Center.
-
Upload
merry-goodwin -
Category
Documents
-
view
227 -
download
1
Transcript of Observational Cosmology Jonathan P. Gardner NASA’s Goddard Space Flight Center.
Wilkinson Microwave Anisotropy Wilkinson Microwave Anisotropy ProbeProbe
Gary Hinshaw, WMAP Co-IUniversity of Edinburgh, September 3, 2004
Beginnings are Important
…(Origins)
... So Are Changes
(Evolution)
David Jonathan Gardner, June 16, 1998 David Jonathan Gardner, June 16, 2005
The First 13.7 Billion Years
Big Bang
Particle Physics
Now
Atoms & Radiation:CMB
First Galaxies
Galaxies Evolve Planets, Life
& Intelligence
380,000 years
3 minutes
1 billion years
13.7 billion years
400 million years
Dark Matter/Dark Energy
7 billion years
Edwin P. Hubble(the man, not the telescope)
Edwin P. Hubble, 1889-1953
1. Classification of Galaxies
2. The “Spiral Nebulae” are “Island Universes”
3. The Universe is Expanding
Which is further away?How can you tell?
The Hubble Sequence• Hubble classified nearby (present-day)
galaxies into Spirals and Ellipticals.
• The Hubble Space Telescope extends this to the distant past.
Measuring Distances
Cepheid Variable Stars: known period-luminosity relation.
Suitable for nearby galaxies
Supernovae: known maximum luminosity. Suitable for distant galaxies.
Astronomers can measure distances if they know the intrinsic luminosity.
Hubble Discovers the Universe
Cepheids in the Andromeda galaxy
showed it is 8 times further than the most distant
star in our Galaxy.
Island Universes!
“Planetary Nebula” are within our
Galaxy.
Hubble at Mount Wilson telescope
Hubble’s Law
Distance in Millions of Light Years
900 1200300 6000
10,0000
20,0000
30,0000
0Velo
city
in K
ilom
ete
rs p
er
Seco
nd
Distance + Light travel time = Seeing the past.
Looking Backwards in Time
Distance
Tim
e
Here & Now
1 Million light years away,
1 Million years ago
1 Billion light years away
1 Billion years ago
Far, Far Away means Long, Long Ago
T1T1 T2T2
Why is the cosmic microwave background temperature so uniform on scales >2°?
T1 = T2 + O (10-5)
>> 2°
D >> c/H o
MAP990008
The Horizon Problem
MAP990007
The Flatness Problem
0 5 10t [Gyr]
Density 1ns after BB
Why is the universe anywhere close to =1 now? =1 is an unstable stationary point.
0
0S
cale
Fac
tor
a(t)
447,225,917,218,507,401,284,015 gm/cc
447,225,917,218,507,401,284,016 gm/cc
447,225,917,218,507,401,284,017 gm/cc
Curved Space-Time
3D Figures by Stuart Levy of the University of Illinois, Urbana-Champaign and by Tamara Munzer of Stanford University for Scientific American. 2D Figures by Ned Wright, UCLA
Flat, or Euclidean Space
Positive Spherical Space
Negative Hyperbolic Space
Smooth 3KCosmic microwavebackground radiation
Clumpy distributionof galaxies -
MAP990012
The Structure Problem
how did this happen?
Inflation solves the problems
Before Inflationcausally connected
quantum fluctuations.
After Inflation,previously connected regions are outside the horizon.
Later, the regions re-enter the horizon.Quantum fluctuations become galaxies
Predictions: Universe is flat. Fluctuations are correlated on different scales.
Synthesis of Light Elements
• Light elements, D, He, Li produced ~3 minutes “after Big Bang”.
• One free parameter in predicted abundances: baryon/photon ratio
(note: baryons = atoms)
• Baryon/photon ratio now measured by CMB (discussed later).
• Predicted abundances may now be confronted with observed abundances (grey boxes). Some tensions.
Why Bright Clumps?Remnants of Primordial Oscillations
Gravity tries tomake matter fall into potential wells
Radiation pressurepushed back...
Oscillations results…
Imprint of eventimparted on photons...
The First 400 Million Years
Barkana & Loeb 2001, Physics Reports, 349, 125
Cooling with atoms
Cooling with H2
3σ
2σ
1σ
The First Galaxies• What did the first galaxies to form look like?
– They are very distant, and very faint.
Infrared Light• Light from the first galaxies is redshifted
from the visible into the infrared.
• Infrared is heat radiation
• Most of the Sun’s energy is visible light
Deepest View(s) of the Universe
• 1995 Hubble Deep Field– 10 days exposure, small area
• 1998 Hubble Deep Field South– Repeat in another field
• 2003 Great Observatories Origins Deep Survey– 30x area– infrared with Spitzer, X-ray with Chandra
• 2004 Hubble Ultra-Deep Field– 30 days exposure, more sensitive camera
• 1996-2006-… Follow-up observations
Hubble Ultra Deep Field
Finding distant galaxies
• UV radiation shortward of Lyman limit at 912Å is absorbed by inter-galactic medium.
• This break is redshifted through successive filters
Infr
are
d
• Visible light technology (CCDs) ends at ~1 micron, so finding galaxies at z>6 requires infrared.
History of star-formation in the UniverseS
tar-
form
atio
n de
nsity
Bouwens et al. 2005, astro-ph/0509641
Prospects for future study at high-z
• Hubble (2.4m diameter warm telescope):– Reaches to z~6, with claims to 7 or 8.– New camera to be installed in next servicing
mission may reach to magnitudes of 28.5 (15 nJy) in the NIR.
– No longer has sensitive spectroscopic capability in opt-NIR.
• Spitzer (0.85m diameter cold telescope):– Reaches to z~6 (same galaxies as HST).– Reaches magnitudes of 26.6 in near- to mid-
IR.
• Ground-based observations (10m warm)– Limited by atmosphere
How to win at Astronomy
108
1600 1700 1800 1900 2000
Gal
ileo
Sensitivity Improvement over the Eye
Year of observations
Telescopes alone
Photographic & electronic detection
106
104
102
Huy
gens
eye
piec
eS
low
f r
atio
s
Sho
rt’s
21.
5”
Her
sche
ll’s
48”
Ros
se’s
72”
Pho
togr
aphy
Mou
nt W
ilso
n 10
0”
Mou
nt P
alom
ar 2
00”
Sov
iet 6
-mAdapted from Cosmic Discovery, M. Harwit
1010
CC
Ds
HS
T JWS
T
Big Telescopes
with Sensitive
Detectors in Space
1610
1665
1796
1926
HST vs. JWST - orbit
375 miles up Second Lagrange Point,1,000,000 miles away
How will JWST get there?
Ariane 5
HST vs. JWST - size
2.4 meter diameter
6.5 meter diameter
How do you put a 6.5 meter mirror in a 5 meter rocket?
When was re-ionization?
Fan et al. 2001, AJ, 122, 2833
Patchy Absorption
Redshift
Wavelength Wavelength Wavelength
Lyman Forest Absorption
Black Gunn-Peterson trough
z<zi
z~zi z>zi
Neutral IGM
.
Kogut et al. 2003, ApJS, 148, 161
Fan et al. 2001, AJ, 122, 2833
Distant Galaxies are “Train Wrecks”
• Trace construction of Hubble sequence:
• How do “train wrecks” become spirals and ellipticals? By Merging!
The Next 20 Years
• What is the cause of inflation?• What is the dark energy?
• How did the Universe begin?• How will it end?
In other words:
Can We Prove Inflation?
• Gravity waves propagating during inflation leave a mark on the polarization of the CMB.
• CMB Polarization mission– Currently being studied.
What is the Dark Energy?
• Hypothesized by Einstein, discovered in 1998, confirmed in 2003.
• 3 potential Nobel Prizes:– Cosmological Constant breaks
standard model of particle physics
– Quintessence means new physics
– Modification of General Relativity
• NASA-DOE Joint Dark Energy Mission– Currently being studied.