Download The Observable Universe: Redshift, Distances and the Hubble-Law

The Observable Universe:
Redshift, Distances and
the Hubble-Law
Max Camenzind
Bremen @ 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 - Cepheids
Some 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. Measure
Period
2. Determine
Luminosity
1. Measure
apparent
magnitude
2.
Distance !
The Luminosity of
the observed Star
~1500L
1923 - Hubble
measures the
Distance to M 31
via Cepheids
Hubble discovers
Cepheids in M 31
Debate
solved!
100-inch Hooker Telescope, Mt. Wilson
Edwin Hubble
The Universe Expands
• Until 1929, the Universe has been
considered to be static (Newton, Einstein).
• 1929: Edwin Hubble published first
Redshifts of Galaxies – RedshiftCorrelation, on the basis of Cepheid
Distances: z = (λB – λG)/λG
• The Universe of Galaxies expands
V=c
z = H d : [H ] = km/s/Mpc
Galaxy
Spectra
have
characteristic
Absorption lines
~ Stars
Spectrum Galaxy
depends on age
z = 4,58
Since 1963: Quasars have characteristic Emission Line Spectra
z = 4,96
Hubble
1929
Hubble  Correlation ?
?
Hubble
Extension
tomorrow
The
Universe
expands
(Hubble
1929)
today
yesterday
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
Hubble
KeyProject
2003
All
Data
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
Standard
Candles
SNe become
as bright as
the centers
Of galaxies.
SN 1994D
CO White Dwarf
at Chandrasekhar
limit
Types of Supernovae in Astronomy
Typical
SN Ia
Maximal
Brightnes
LightcurvesWidth
(Stretching)
Accretion onto WD  SN Ia
Red giant
•
•
•
•
White
Dwarf
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? ]
SN Ia
as
Standard
Candle
The
brighter
the
Slower
Lightcurves of SN Ia
10 Billion eL
Absolute Magnitude: ~ -19,5 mag
e
Radioactive Decay of
56
Ni
9 days
Similarity
Ni 
56
56
Co
Fe delays cooling
56
112 days 56
Fe
+ e+
Standard
Candle
SNe Ia Calibration
SN
Galaxy
1937C
IC 4182
1960F
NGC 4496A
1972E
NGC 5253
1974G
NGC 4414
1981B
NGC 4536
1989B
NGC 3627
1990N
NGC 4639
1998bu
NGC 3368
1998aq
NGC 3982
Straight mean
Weighted mean
m-M
MB
MV
28.36 (12)
31.03 (10)
28.00 (07)
31.46 (17)
31.10 (12)
30.22 (12)
32.03 (22)
30.37 (16)
31.72 (14)
-19.56 (15)
-19.56 (18)
-19.64 (16)
-19.67 (34)
-19.50 (18)
-19.47 (18)
-19.39 (26)
-19.76 (31)
-19.56 (21)
-19.57 (04)
-19.56 (07)
-19.54 (17)
-19.62 (22)
-19.61 (17)
-19.69 (27)
-19.50 (16)
-19.42 (16)
-19.41 (24)
-19.69 (26)
-19.48 (20)
-19.55 (04)
-19.53 (06)
MI
-19.27 (20)
-19.21 (14)
-19.14 (23)
-19.43 (21)
∆ m15
0.87 (10)
1.06 (12)
0.87 (10)
1.11 (06)
1.10 (07)
1.31 (07)
1.05 (05)
1.08 (05)
1.12 (03)
-19.26 (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
canshapes,
be normalised
through
evolution
 light curve
colours, spectroscopy
theirlight
curve
shapes (102 objects)
dust
colours,
spectroscopy
excellent relative distances (Phillips 1993, Hamuy et al.
gravitational
lensing  difficult, need mapping of
1996, Riess et al. 1996, 1998, 1999, Perlmutter et al. 1997, Phillips
light beam
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,
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
H 0 = 70 ± 10
km
s ⋅ Mpc
The nearby SN Ia Sample
Evidence for good
distances
z > 0.1  Friedmann Cosmology
Assumption:
homogeneous and isotropic universe
Null geodesic in a Friedmann-Robertson-Walker
metric:
− 1
z

DL =
Ω
(1 + z )c
H0 Ω
M
κ

S Ω

κ
8π G
=
ρM
2
3H 0
∫ [Ω
κ
(1 + z ′ ) 2 + Ω
3
′
(
1
+
z
)
+ Ω
M
Λ
]
0
Ω
2
k
kc
= − 2 2
R H0
Ω
Λc
=
2
3H 0
2
Λ
2


dz ′ 

Supernovae
Projects
SN Factory
Carnegie SN Project
SDSSII
ESSENCE
CFHT Legacy Survey
Higher-z SN Search
(GOODS)
JDEM/LSST / Satellit
Plus local Projects:
LOTOSS, CfA, ESC
Distanzmodul
Cosmic Supernovae z < 2
Details will
depend on
expansion
law for the
Universe.
Riess et al. 2007
Hubble-Diagram with SDSSII SNe
arXiv:0908.4274
Deviations
from Hubble-Law
 cosmic Expansion
z=3
z=2
H
le
b
ub
z=1
Distance in 1000 Mpc
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
Supernovae
Acceleration
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.