dark matter in the universe: observational evidence dark matter in the universe: observational...

Dark matter in the Dark matter in the

Universe: observational Universe: observational evidenceevidence

Dark side of the Universe

Weighting of the UniverseDark matter – observationsDark energy - observations

Luminous and dark sides of the Universe in today's cosmology

History of the Universe

http://map.gsfc.nasa.gov/m_mm.html

Weighting of the UniverseI. Density parameter

Friedman equation (without a cosmological constant)

Critical density for which k=0 (flat geometry)

Present value:

Density parameter:

Weighting of the UniverseI. Density parameter

Friedman equation with a cosmological constant:

Leads to:

Weighting the Universe – important and not so easy

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

Weighting the UniverseI. Time – redshift relation

Hubble Law:

But generally:

Which affects also luminosity, angular size etc.

Weighting the UniverseCounting baryons

Stars in galaxies:

Hot gas in clusters: ~0.05 Hydra A :

optyka - NASA/CXC/SAO X - La Palma/B. McNamararadio - Greg Taylor, NRAO

II. Observational evidence for the existence of dark matter

Rotation curves in spiral galaxies and velocity dispersion in eliptical galaxies

Velocities of galaxies in clusters Temperature distribution in clusters Lensing of background objects on clusters Nucleosynthesis Large Scale Structure of the Universe CMBR anisotropy

IIa. 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:

IIa. Rotation curves of galaxies

IIb. Velocities in galaxies in 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/SDSS

IIc. 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

IId. 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

IId. Gravitational lensing on clusters

IId. Gravitational lensing on clusters

•Cluster of galaxies 1E 0657-56 (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

Bullet Cluster

Cosmic Evolution Project (COSMOS): HST, Masey et al. 2007, Nature

Weak lensing -> 3D dark matter distribution; “naked clumps” of dark matter?

IIe. 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.

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

IIf. 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).

IIg. Cosmic Microwave Background Radiation

– z~1100

– ~380 000 years after BB

– Recombination – last scattering surface

– T~3000K -< T~2.7 K

– Inhomogeneities (anisotropy) ~10^(-5)

IIg. 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

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

IV. Dark energy

Geometry of the Universe and the luminosity of Ia supernovae

White dwarf exceeding the Chandrasekhar mass as a standard candle

Komatsu, et al. 2005

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).

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

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

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

Borgani & Guzzo 2001

IV. LSS evolution: with and without dark energy

Summary – the dark sector of the Universe

Possibilities:baryonic DM (old stars, MACHO etc.)

problems:• Microlensing experimentsnucleosynthesisPrimordial 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)

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

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.

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.

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.

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.

Symulacje Millenium (Springel et al. 2005)Symulacje Millenium (Springel et al. 2005)

0.21 mld lat po powstaniu Wszechświata

Symulacje Millenium (Springel et al. 2005)Symulacje Millenium (Springel et al. 2005)

1 mld lat po powstaniu

Wszechświata

Symulacje Millenium (Springel et al. 2005)Symulacje Millenium (Springel et al. 2005)

4,7 mld lat po powstaniu

Wszechświata

Symulacje Millenium (Springel et al. 2005)Symulacje Millenium (Springel et al. 2005)

Dziś, czyli 13,5 mld lat

po powstaniu Wszechświata