The Observable Universe:Redshift, Distances and

the Hubble-Law

Max CamenzindBremen @ Sept 2010

Key Facts Universe• 1. The Universe is expanding and presently

even accelerating. Hubble Expansion: Space is stretched This implies some beginning …

• 2. Relic Radiation: CMBR, WMAP, …• 3. Matter distribution is clumpy• 4. Matter is dominated by Dark Matter

(DM). Only a Relativistic Cosmos can explain

all these facts.

1. The Universe is Expanding• Until 1929, the Universe of galaxies

was thought to be static.• In 1929, Edwin Hubble published the

first distance – redshift correlation, based on Cepheid distances for the galaxies. The Universe of galaxies is expanding: c*z = H0*d : [H0] = km/s/Mpc

Hubble Expansion Expansion of Space

Variable Stars - CepheidsSome stars show intrinsic magnitude

variations, not due to ecclipses in binary systems.

Important Example:δ Cephei

Lightcurve of δ Cephei

Henrietta Leavitt (1868-1921) discovered Cepheids Period-Luminosity (PL) Relation (1912)

Lightcurve of Cepheids

Large & Small Magellanic Clouds Period versus Magnitude of Cepheids in

SMC

Cepheids as Distance Indicator

The “Period” (Duration) of Pulsation correlates with the Luminosity

1.1. Measure Measure PeriodPeriod

2.2. DetermineDetermine LuminosityLuminosity1.1. Measure Measure

apparent apparent magnitudemagnitude

2.2. Distance Distance !!

The Luminosity of the observed Star ~1500L

1923 - Hubble measures the

Distance to M 31 via Cepheids

100-inch Hooker Telescope, Mt. Wilson

Edwin Hubble

Debate solved!Hubble discovers

Cepheids in M 31

The Universe Expands

• Until 1929, the Universe has been considered to be static (Newton, Einstein).

• 1929: Edwin Hubble published first Redshifts of Galaxies – Redshift-Correlation, on the basis of Cepheid Distances: z = (λB – λG)/λG

• The Universe of Galaxies expands V = c z = H0 d : [H0] = km/s/Mpc

GalaxySpectra

havecharac-teristic

Absorp-tion lines~ Stars

Spectrum Galaxydepends on age

Since 1963: Quasars have characteristic Emission Line Spectra

z = 4,58

z = 4,96

Hubble1929

Hubble Correlation ?

?

Hubble Extension

TheUniverseexpands(Hubble1929)

today

yesterday

tomorrow

Big Bang

Woody Allen

„If the Universe expands - why can I not find a parking lot ?“

Answer: ???

Source: Web, http://www.monerohernandez.com/GALERIA/woodyallen.html

Ad History of H0

The 2nd Great Debate …

Hubble Key Project (2001)

H0 = 72 +/- 8

Solution

HubbleKey-Project2003

AllData

Meaning of the Hubble Constant

• 1. H0 determines the Scale of the Universe: RH = c/H0 = 4200 Mpc : Hubble-Radius observable Universe is therefore limited.

• 2. H0 determines the age of the Universe: tH = 1/H0 = 14 Billion years: Hubble-Age, effective age depends on density.

• Important: The Hubble-age is only a measure for the true age of the Universe!

• This age depends on many other Parameters (see LCDM model)!

The Cosmic Distance Ladder• Parallax: ~500 pc (Hipparcos), 100 kpc (GAIA)• Spectroscopic Parallax (via Distance module): 10 kpc• RR Lyrae Stars: ~100 kpc• Cepheids (104 LS): ~ 30 Mpc • Typ 1a Supernovae (109 LS): 10,000 Mpc

GAIA

Distances for Galaxies

• Geometrical Distances (mostly impossible).• Standard-Candles: d² = L / 4π f• (i) RR-Lyrae Stars (~ 0,5 Solar mass),

Riesensterne der Spektralklasse A, F, Pulsationsveränderliche (h Bereich)

• (ii) Delta Cephei Stars ( < 20 Mpc)• (iii) brightest stars (not well defined)• (iv) Central stars in Planetary nebulae• (v) Supernovae of Typ Ia ( z < 2 )

SN Ia as StandardCandles

SNe becomeas bright asthe centersOf galaxies.

SN 1994D CO White Dwarfat Chandrasekharlimit

Types of Supernovae in Astronomy

Typical SN Ia

Maximal Brightnes

Lightcurves-Width

(Stretching)

Accretion onto WD SN Ia

• White dwarf accretes H of the Red Giant• H fusion He Form a Helium shell• Mass can accumulate Chandrasekhar limit• [ What is the Chandrasekhar limit? ]

Red giant White Dwarf

SN Iaas

StandardCandle

-The

brighterthe

Slower

Lightcurves of SN IaAbsolute Magnitude: ~ -19,5 mag

Radioactive Decay of 56Ni 56Fe delays cooling

56Ni 56Co 56Fe + e+9 days 112 days

Similarity Standard Candle

e

10 Billion Le

SNe Ia CalibrationSN Galaxy m-M MB MV MI ∆ m15

1937C IC 4182 28.36 (12) -19.56 (15) -19.54 (17) 0.87 (10)1960F NGC 4496A 31.03 (10) -19.56 (18) -19.62 (22) 1.06 (12)1972E NGC 5253 28.00 (07) -19.64 (16) -19.61 (17) -19.27 (20) 0.87 (10)1974G NGC 4414 31.46 (17) -19.67 (34) -19.69 (27) 1.11 (06)1981B NGC 4536 31.10 (12) -19.50 (18) -19.50 (16) 1.10 (07)1989B NGC 3627 30.22 (12) -19.47 (18) -19.42 (16) -19.21 (14) 1.31 (07)1990N NGC 4639 32.03 (22) -19.39 (26) -19.41 (24) -19.14 (23) 1.05 (05)1998bu NGC 3368 30.37 (16) -19.76 (31) -19.69 (26) -19.43 (21) 1.08 (05)1998aq NGC 3982 31.72 (14) -19.56 (21) -19.48 (20) 1.12 (03)Straight mean -19.57 (04) -19.55 (04) -19.26 (06)Weighted mean -19.56 (07) -19.53 (06) -19.25 (09)

Saha et al. 1999

Type Ia Supernovae Projects

• Establish a cosmological distance indicator in the local universe (z < 0.1)

Type Ia Supernovae can be normalised through their light curve shapes (102 objects)

excellent relative distances (Phillips 1993, Hamuy et al. 1996, Riess et al. 1996, 1998, 1999, Perlmutter et al. 1997, Phillips et al. 1999, Suntzeff et al. 1999, Jha et al. 1999, 2003)

Measure objects at cosmological distances

>120 distant SNe Ia (0.3<z<1.0) published (Garnavich et al. 1998, Riess et al. 1998, Perlmutter et al. 1997, 1999, Tonry et al. 2003, Suntzeff et al. 2004, Barris et al. 2004,

Leibundgut et al. 2004, Astier 2005 (SNLegacy))

evolution light curve shapes, colours, spectroscopydust colours, spectroscopygravitational lensing difficult, need mapping of light beam

Distances in locale Universe

• Expansion is linear: Hubble-Law

• v = cz = H0·D• Use Distance Modulus

• µ = m - M = 5 log(D/10 pc)• Distances for ‘Standard Candles’ (M=const.)

• m = 5 log(z) + b• b = M + 25 – 5 log([c/H0] / Mpc)

Hubble-Diagram of SN Ia

m = 5 log10(cz) + b

MpcskmH

⋅±= 10700

The nearby SN Ia Sample

Evidence for gooddistances

z > 0.1 Friedmann CosmologyAssumption:homogeneous and isotropic universe

Null geodesic in a Friedmann-Robertson-Walker metric:

[ ]

′Ω+′+Ω+′+ΩΩΩ

+=−

Λ∫ zdzzSH

czDz

ML

21

0

32

0

)1()1()1(κκ

κ

MM HG ρπ

203

8=Ω20

2

2

HRkc

k −=Ω 20

2

3HcΛ=Ω Λ

Supernovae Projects

ESSENCECFHT Legacy Survey

Higher-z SN Search(GOODS)

SN FactoryCarnegie SN ProjectSDSSII

JDEM/LSST / Satellit

Plus local Projects:LOTOSS, CfA, ESC

Cosmic Supernovae z < 2

Riess et al. 2007

Dis

tanz

mod

ul

Details willdepend onexpansion law for the Universe.

Hubble-Diagram with SDSSII SNe

arXiv:0908.4274

Dev

iati

ons

from

Hub

ble-

Law

c

osm

ic E

xpan

sion

Hubble

Distance in 1000 Mpc

z = 1

z = 2

z = 3

Nature of the Dark Energy?

The Future

• Future experiments will distinguish between a cosmological constant or quintessence– ESSENCE, CFHT Legacy Survey, VST,

VISTA, NGST, LSST, SNAP

SupernovaeAcceleration Probe –SNAP

Summary on Hubble

• Measuring Hubble expansion needs to measure distances beyond Virgo cluster measure expansion of Coma cluster against Virgo!

• SN Ia obviously are very good standard candles (since 1998) are observable for z < 2.

• Calibration error < 0.1 mag possible?

Summary• Most of galaxies and all Quasars have redshifted

Spectra (cosmological redshift, not gravitational).• Hubble found: cz = H0 d , z < 0,1.• The Hubble Constant has to be calibrated: Cepheids

and SN-Methods are nowadays the most important Distance Indicators: H0 = 72+/-5 km/s/Mpc.

• Hubble-Law can be used to measure distances in the Universe upto z < 0.2. For z > 0,2 quadratatic deviations (see LCDM).

• With this method, the Homogeneity and Isotropy of the Universe also follows from the galaxy distribution for Scales s > 200 Mpc.