Observational Cosmology

Jonathan P. GardnerNASA’s Goddard Space Flight Center

Wilkinson Microwave Anisotropy Wilkinson Microwave Anisotropy ProbeProbe

Gary Hinshaw, WMAP Co-IUniversity of Edinburgh, September 3, 2004

Hubble Space Telescope

James Webb Space Telescope

Astronomical Search For Origins

Big BangFirst Galaxies

Galaxies Evolve

Stars

Planets

Life

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

Doppler Shift

Hubble’s Law

Distance in Millions of Light Years

900 1200300 6000

10,0000

20,0000

30,0000

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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

The First Nano-Second

How much of the Universe can we see?

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

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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

Inflation and a Flat Universe

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.

The First

Three Minute

s

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.

The First 380,000 Years

Wayne Hu and Martin White, Scientific American, February 2004

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...

Sound Waves in the Plasma

Baby Picture of the Universe

WMAP shows the Universe is Flat

Flatness

Baryons

Dark Matter

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

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

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Sensitivity Improvement over the Eye

Year of observations

Telescopes alone

Photographic & electronic detection

106

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Big Telescopes

with Sensitive

Detectors in Space

1610

1665

1796

1926

HST vs. JWST - temperature

Room Temperature -225° Celsius,-370° Fahrenheit

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?

The First 1 Billion Years

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

The First 7 Billion Years

M81 by Spitzer

Distant Galaxies are “Train Wrecks”

• Trace construction of Hubble sequence:

• How do “train wrecks” become spirals and ellipticals? By Merging!

Galaxy Mergers

The Last 7 Billion Years

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.

Observational Cosmology

Jonathan P. Gardner

NASA’s Goddard Space Flight Center