the observable universe: redshift, distances and …€¦ · the observable universe: redshift,...
TRANSCRIPT
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The Observable Universe:Redshift, Distances and
the Hubble-Law
Max CamenzindBremen @ Sept 2010
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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.
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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
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Hubble Expansion Expansion of Space
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Variable Stars - CepheidsSome stars show intrinsic magnitude
variations, not due to ecclipses in binary systems.
Important Example:δ Cephei
Lightcurve of δ Cephei
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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
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Cepheids as Distance Indicator
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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
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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
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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
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GalaxySpectra
havecharac-teristic
Absorp-tion lines~ Stars
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Spectrum Galaxydepends on age
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Since 1963: Quasars have characteristic Emission Line Spectra
z = 4,58
z = 4,96
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Hubble1929
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Hubble Correlation ?
?
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Hubble Extension
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TheUniverseexpands(Hubble1929)
today
yesterday
tomorrow
Big Bang
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Woody Allen
„If the Universe expands - why can I not find a parking lot ?“
Answer: ???
Source: Web, http://www.monerohernandez.com/GALERIA/woodyallen.html
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Ad History of H0
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The 2nd Great Debate …
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Hubble Key Project (2001)
H0 = 72 +/- 8
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Solution
HubbleKey-Project2003
AllData
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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)!
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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
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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 )
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SN Ia as StandardCandles
SNe becomeas bright asthe centersOf galaxies.
SN 1994D CO White Dwarfat Chandrasekharlimit
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Types of Supernovae in Astronomy
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Typical SN Ia
Maximal Brightnes
Lightcurves-Width
(Stretching)
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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
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SN Iaas
StandardCandle
-The
brighterthe
Slower
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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
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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
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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
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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)
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Hubble-Diagram of SN Ia
m = 5 log10(cz) + b
MpcskmH
⋅±= 10700
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The nearby SN Ia Sample
Evidence for gooddistances
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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
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Supernovae Projects
ESSENCECFHT Legacy Survey
Higher-z SN Search(GOODS)
SN FactoryCarnegie SN ProjectSDSSII
JDEM/LSST / Satellit
Plus local Projects:LOTOSS, CfA, ESC
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Cosmic Supernovae z < 2
Riess et al. 2007
Dis
tanz
mod
ul
Details willdepend onexpansion law for the Universe.
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Hubble-Diagram with SDSSII SNe
arXiv:0908.4274
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Dev
iati
ons
from
Hub
ble-
Law
c
osm
ic E
xpan
sion
Hubble
Distance in 1000 Mpc
z = 1
z = 2
z = 3
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Nature of the Dark Energy?
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The Future
• Future experiments will distinguish between a cosmological constant or quintessence– ESSENCE, CFHT Legacy Survey, VST,
VISTA, NGST, LSST, SNAP
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SupernovaeAcceleration Probe –SNAP
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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?
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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.