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Dark matter in the Universe: observational evidence Dark matter in the Universe: observational evidence.

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Prezentacja na temat: "Dark matter in the Universe: observational evidence Dark matter in the Universe: observational evidence."— Zapis prezentacji:

1 Dark matter in the Universe: observational evidence Dark matter in the Universe: observational evidence

2 Dark side of the Universe Weighting of the Universe Dark matter – observations Dark energy - observations Luminous and dark sides of the Universe in today's cosmology

3 History of the Universe

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5 Weighting of the Universe I. Density parameter  Friedman equation (without a cosmological constant)‏  Critical density for which k=0 (flat geometry)‏  Present value:  Density parameter:

6 Weighting of the Universe I. Density parameter  Friedman equation with a cosmological constant:  Leads to:

7 Weighting the Universe  The main problem: there is almost no possibility to measure the distance directly. In the cosmological context, almost always distance == z. –Time-redshift relation:

8 Weighting the Universe I. Time – redshift relation  Hubble Law:  But generally:  Which affects also luminosity, angular size etc.

9 Weighting the Universe Counting baryons  Stars in galaxies:  Hot gas in clusters: ~0.05  Hydra A : optyka - NASA/CXC/SAOX - La Palma/B. McNamara radio - Greg Taylor, NRAO

10 Observational evidence for the existence of dark matter  Rotation curves in spiral galaxies  Velocity dispersion in elliptical galaxies  Spiral galaxies made from bulge and disk are unstable as self- gravitation systems  Velocity dispersion of galaxies in clusters  Temperature distribution in clusters  Lensing of background objects on clusters  Primordial nucleosynthesis -> if DM exists, it cannot be baryonic

11 Observational evidence for the existence of dark matter  Other:  Large Scale Structure of the Universe: if dark matter is baryonic only (or hot), structure forms too late – we would not exist  CMBR anisotropies: standard ruler; the density of the Universe should be close to the closure density

12 Rotation curves of galaxies  But: stars in galaxies do not obey this law  Stars in elliptical galaxies: too high velocities  Conclusion: additional mass -> halo made of additional (dark) matter Begeman 1989 John Vickery and Jim Matthes/Adam Block/NOAO/AURA/NSF NGC 3198 –Kepler's law:

13 Rotation curves of galaxies

14 Velocities in galaxies in (regular, virialized) clusters –The nearest irregular cluster: Virgo (~18 Mpc)‏ –The nearest regular cluster: Coma (~90 Mpc)‏ |~1000 bright galaxies, 85% of early types (ellipticals) Velocity dispersion ~1000 km/s ~ escape velocity; but the cluster is relaxed M/L ~ 3-10 A Sloan Digital Sky Survey/Spitzer Space Telescope image of the Coma Cluster in ultraviolet and visible light; NASA/JPL-Caltech/GSFC/SDSSSloan Digital Sky SurveySpitzer Space TelescopeultravioletvisibleNASAJPLCaltechGSFCSDSS

15 Temperature distribution of hot gas in clusters Abell 2029 –Temperature distribution -> assuming the state of hydrostatic equilibriumium and a perfect hydrogen gas -> distribution of matter -> gravitational potential X-ray: NASA/CXC/UCI/A.Lewis et al. Optical: Pal.Obs. DSS –Mass/light ~ 10 T~4*10^7

16 Gravitational lensing on clusters Lensing Strong: large mass, close source effect: multiple image, Einstein's rings, arcs weak: effect: elongating, magnifying of an image; statistics of this effect can give us the information about the mass distribution in the lens Microlensing: brightening Abell 1689, NASA HST

17 IId. Gravitational lensing on clusters

18 Cluster of galaxies 1E (Bullet Cluster) has been created as a result of a collision of two clusters. In the image we can see hot gas (red) belonging to it and stars. Lensing of the light of distant objects from the background allows to reconstruct the mass distribution in the cluster: most mass (blue colour) is where gas and stars and least abundant X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al

19 Bullet Cluster

20 Cosmic Evolution Project (COSMOS): HST, Masey et al. 2007, Nature Weak lensing -> 3D dark matter distribution; “naked clumps” of dark matter?

21 Primordial nucleosynthesis  In the early phase of its existence (t~1s, T ~10^8 – 10^6) the Universe has been hot enough that the processes of nuclear fusion were possible in it. 1H -> 2H -> 3He -> 4He -> 5Li -> 6Li -> 7Li -> 8Be -> 9Be  Relative aboundances of these element depend on relative densities of protons, neutrons, electrons, neutrons and photons during the nucleosynthesis, as well as on the total baryon density.

22 IIe. Primordial nucleosythesis  Nucleosynthesis – the limit on the total amount of baryons: –It is in a good agreement with the observations of stars + dust + gas in galaxies and clusters. –Dark matter (from all the previously cited arguments) is ~10x more

23 The Large Scale Structure of the Universe –Equations of structure (continuity, Euler, Poisson) - > numerical solution cannot produce present-day structure with the “right: density of baryons –Moreover: dark matter should be “cold”, not “hot” simulations were performed at the National Center for Supercomputer Applicationsby Andrey Kravtsov (The University of Chicago) and Anatoly Klypin (New Mexico State University).National Center for Supercomputer ApplicationsAndrey KravtsovThe University of ChicagoAnatoly KlypinNew Mexico State University

24 Cosmic Microwave Background Radiation – z~1100 –~ years after BB –Recombination – last scattering surface –T~3000K -< T~2.7 K –Inhomogeneities (anisotropy) ~10^(-5)‏

25 Cosmic Microwave Background Radiation – Power spectrum –Inhomogeneities in CMB –Acoustic oscillations in the plasma (photon pressure against baryon gravity) + secondary anisotropies –Baryons' density: Omega_B~0.02

26 IV. Dark energy Standard candles Supernovae (Type Ia) Standard rulers Alcock-Paczynski and Ly-a. CMB acoustic peak locations. Peak of the matter spectrum Baryon oscillations Lensing cross-correlation tomography Growth & distance Number counts (e.g. clusters)‏ Weak lensing tomography Cluster CMB polarization/ISW effect

27 IV. Dark energy  Geometry of the Universe and the luminosity of Ia supernovae  White dwarf exceeding the Chandrasekhar mass as a standard candle

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29 Komatsu, et al. 2005

30 IV. Dark energy –Alcock-Paczyński test  Basic Idea: Ratio of observed angular size to radial/redshift size varies with cosmology. Find something which is known to be isotropic (i.e. where where transverse and radial intrinsic size are the same). Fixing the ratio of the intrinsic radial and transverse distances gives a relation between the measured radial and transverse distances depending on cosmological parameters (in particular, Omega_Lambda).

31 IV. Dark energy –Alcocka-Paczyński test  Measurements:  1. galaxies  2. quasars  3. Lyman-alpha forest  * What one measures (simple relation between density and optical depth)‏  4.QSO pairs

32 IV. Dark energy –CMB anisotropies  The position of peaks depends on the cosmological model  In particular, the third peak is sensitive to the value of a cosmological constant

33 IV. Dark energy – baryonic oscillations (BAO)‏  Idea: acoustic peaks present in the early plasma should be “preserved” in the present-day structure but just observed on much larger scales

34 Borgani & Guzzo 2001 IV. LSS evolution: with and without dark energy

35 Summary – the dark sector of the Universe Possibilities: baryonic DM (old stars, MACHO etc.)‏ problems: Microlensing experiments nucleosynthesis Primordial black holes: allow to avoid the problem of nucleosynthesis), but they should be evaporating around now... non-baryonic DM: Hot, e.g. neutrinos (but: problems to create large scale structure)‏ Cold (WIMPs, axions, gravitons, SUSY, “shadow Universe” particles)‏ Modified gravity (but: problem with lensing on clusters)

36 Summary – the dark sector of the Universe Possibilities: Dark energy as a cosmological constant (“energy of vacuum” etc.); problem: most of models (quantum field theory)predicts that it should be much higher, Quintesence (a scalar field, may change in time and space); problem of coincidence: why the acceleration of the expansion of the Universe started in such a “right” moment for us? Modified gravity

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38 Od fluktuacji do galaktyk – “hierarchiczny model powstawania wielkoskalowej struktury Wszechświata” Halo rosną i niekiedy łączą się, tworząc większe struktury. Rozwój struktur od mniejszych do większych określa się mianem modelu hierarchicznego. Model ten uznawany jest dziś za najbardziej wiarygodny model rozwoju struktury.

39 Od fluktuacji do galaktyk – “hierarchiczny model powstawania wielkoskalowej struktury Wszechświata” Gry formują się halo ciemnej materii, jest w nich też gaz, złożony z normalnej, znanej nam materii. Ten gaz również gromadzi się i skupia. Gdy osiągnie dostateczną gęstość, tworzą się z niego gwiazdy. Gwiazdy i otaczający je gaz formują pierwsze galaktyki.

40 Od fluktuacji do galaktyk – “hierarchiczny model powstawania wielkoskalowej struktury Wszechświata” Niekiedy halo ciemnej materii łączą się, tworząc większe halo. Zasiedlające je galaktyki zamieszkują wtedy w tym samym halo. Jednak nie łączą się ze sobą równie łatwo jak halo ciemnej materii, ze względu na ciśnienie gazu.

41 Od fluktuacji do galaktyk – “hierarchiczny model powstawania wielkoskalowej struktury Wszechświata” Z czasem halo łączą się coraz bardziej. W niektórych znajdują się galaktyki, w innych nie. W końcu także niektóre galaktyki zlewają się, tworząc większe galaktyki. Uważa się, że dzisiejsze wielkie galaktyki (M~10^12 M_sun) powstały w ten sposób.Największe dzisiejsze halo (zawierające gromady galaktyk) mają M~10^15 M_sun.

42 Symulacje Millenium (Springel et al. 2005)‏ 0.21 mld lat po powstaniu Wszechświata

43 Symulacje Millenium (Springel et al. 2005)‏ 1 mld lat po powstaniu Wszechświata

44 Symulacje Millenium (Springel et al. 2005)‏ 4,7 mld lat po powstaniu Wszechświata

45 Symulacje Millenium (Springel et al. 2005)‏ Dziś, czyli 13,5 mld lat po powstaniu Wszechświata


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