The Observable Universe: Redshift, Distances and the Hubble-Law. Max Camenzind Sept 2010

Transcription

1 The Observable Universe: Redshift, Distances and the Hubble-Law Max Camenzind Sept 2010

2 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.

3 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

4 Hubble Expansion Expansion of Space

5 Variable Stars - Cepheids Some stars show intrinsic magnitude variations, not due to ecclipses in binary systems. Important Example: δ Cephei Lightcurve of δ Cephei

6 Henrietta Leavitt ( ) discovered Cepheids Period-Luminosity (PL) Relation (1912) Lightcurve of Cepheids Large & Small Magellanic Clouds Period versus Magnitude of Cepheids in SMC

7 Cepheids as Distance Indicator

8 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

9 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

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11 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

12 Galaxy Spectra have characteristic Absorption lines ~ Stars

13 Spectrum Galaxy depends on age

14 z = 4,58 Since 1963: Quasars have characteristic Emission Line Spectra z = 4,96

15 Hubble 1929

16 Hubble Correlation??

17 Hubble Extension

18 tomorrow The Universe expands (Hubble 1929) today yesterday Big Bang

19 Woody Allen If the Universe expands - why can I not find a parking lot? Answer:??? Source: Web,

20 Ad History of H0

21 The 2nd Great Debate

22 Hubble Key Project (2001) H0 = 72 +/- 8

23 Solution Hubble KeyProject 2003 All Data

24 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)!

25 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

26 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 )

27 SN Ia as Standard Candles SNe become as bright as the centers Of galaxies. SN 1994D CO White Dwarf at Chandrasekhar limit

28 Types of Supernovae in Astronomy

29 Typical SN Ia Maximal Brightnes LightcurvesWidth (Stretching)

30 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? ]

31 SN Ia as Standard Candle The brighter the Slower

32 Lightcurves of SN Ia 10 Billion el Absolute Magnitude: ~ -19,5 mag e Radioactive Decay of 56 Ni 9 days Similarity Ni Co Fe delays cooling days 56 Fe + e+ Standard Candle

33 SNe Ia Calibration SN Galaxy 1937C IC F NGC 4496A 1972E NGC G NGC B NGC B NGC N NGC bu NGC aq NGC 3982 Straight mean Weighted mean m-m MB MV (12) (10) (07) (17) (12) (12) (22) (16) (14) (15) (18) (16) (34) (18) (18) (26) (31) (21) (04) (07) (17) (22) (17) (27) (16) (16) (24) (26) (20) (04) (06) MI (20) (14) (23) (21) m (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) (06) (09) Saha et al. 1999

34 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,

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36 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 log([c/h0] / Mpc)

37 Hubble-Diagram of SN Ia m = 5 log10(cz) + b H 0 = 70 ± 10 km s Mpc

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39 The nearby SN Ia Sample Evidence for good distances

40 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

41 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

42 Distanzmodul Cosmic Supernovae z < 2 Details will depend on expansion law for the Universe. Riess et al. 2007

43 Hubble-Diagram with SDSSII SNe arxiv:

44 Deviations from Hubble-Law cosmic Expansion z=3 z=2 H le b ub z=1 Distance in 1000 Mpc

45 Nature of the Dark Energy?

46 The Future Future experiments will distinguish between a cosmological constant or quintessence ESSENCE, CFHT Legacy Survey, VST, VISTA, NGST, LSST, SNAP

47 Supernovae Acceleration Probe SNAP

48 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?

49 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.