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Cosmology : Cosmic Microwave Background & Large scale structure. Lec . 1: Background universe. Cosmology IUCAA VSP program ( May 18-22, 2012). Tarun Souradeep. I.U.C.A.A . The Realm of Cosmology. Basic unit: Galaxy. Size : 10-100 kilo parsec (kpc.)
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Cosmology : Cosmic Microwave Background & Large scale structure Lec. 1: Background universe Cosmology IUCAA VSP program (May 18-22, 2012) Tarun Souradeep I.U.C.A.A.
The Realm of Cosmology Basic unit: Galaxy Size : 10-100 kilo parsec (kpc.) Mass : 100 billion Stars Measure distances in light travel time 1 pc. (parsec) = 200,000 AU = 3.26 light yr. Measure Mass in Solar mass Andromeda Galaxy
The Realm of Cosmology 100 million Light years
The Realm of Cosmology 500 million Light years
The Realm of Cosmology 5 Billion Light years
How can we even hope to comprehend this immensely large& complex Universe !?! Look for an appropriate simple model
Modeling nature Picasso: Steiren series
The Isotropic Universe Distribution of galaxies on the sky is broadly isotropic • Isotropy around every point • implies • Homogeneity • Cosmological principle • FLRW models South North Lick Observatory survey
The Expanding Universe Leads to the Hubble’s law Recession velocity is Proportional to the distance Matter density: 1/V Radiation density: 1/(V L) Early Universe is radiation dominated E Einstein’s General relativity applied to an uniform distribution of matter on cosmic scales leads to a smooth expanding universe (FRW Cosmology) Fig.: Ned Wright
The Expanding Universe Fig.: Ned Wright
Space-time of the cosmos Fig.: Ned Wright
Space-time of the cosmos General relativity allows us to formulate physics in any coordinates Fig.: Ned Wright
Space-time of the cosmos Comoving spatial coordinates Fig.: Ned Wright
Space-time of the cosmos Conformal time Comoving spatial coordinates Fig.: Ned Wright
Cosmological Redshift Observer Distant galaxy Equal time events at a distant galaxy appears time-dilated Frequency of light from a distant galaxy is scaled by the expansion Redshift, z=v/c Redshift is related to distance Fig.: adapted from Ned Wright
Expanding Universe Hubble’s law: Recession velocity of galaxies is proportional to the distance Hubble’s measurements in 1929 Frequency of light from a distant galaxy Redshift, z=v/c Redshift is related to distance Fig.: Ned Wright
Expanding Universe Hubble’s Law: Current observational status Fig.: Ned Wright
Cosmic Microwave Background Pristine relic of a hot, dense & smooth early universe - Hot Big Bang model Post-recombination :Freely propagating through (weakly perturbed) homogeneous & isotropic cosmos. Pre-recombination : Tightly coupled to, and in thermal equilibrium with, ionized matter. (text background: W. Hu)
Cosmic “Super–IMAX” theater 0.5 Mega-years 43 Billion Light-years Here & Now (14 Giga-years) Transparent universe Opaque universe
The Isotropic Universe Cosmic Microwave Background Nobel prize 1978 Serendipitous discovery of the dominant Radiation content of the universe as an extremely isotropic, Black-body bath at temperature T0=2.725 (+/-0.002)K . “Clinching support for Hot Big Bang model”
Cosmic Microwave Background The dominant radiation component in the universe ~ 400 CMB photons per cubic cm. (D. Scott ’99)
“Dust” in an expanding box Size = ¼ Number density x 64 Energy density x 64 Size = ½ Number density x 8 Energy density x 8 time Radiation in an expanding box Matter density: 1/V Radiation density: 1/(V L) Early Universe is radiation dominated E Size = ¼ Number density x 64 Energy density x 128 Temperature x 4 Size = ½ Number density x 8 Energy density x 16 Temperature x 2 time
Cosmic Microwave Background The most perfect Black-Body spectrum in nature COBE –FIRAS The CMB temperature – A single number characterizes the radiation content of the universe!! COBE website
Geometry of the Universe Spherical Universe Constant positive curvature Hyperbolic Universe Constant negative curvature Flat Universe
`Standard’ cosmological model: Geometry, Expansion & Matter Clustering matter Non-Clustering matter
How much do we now know about this model Universe ? lots !!!
Good old Cosmology, … New trend ! Total energy density Baryonic matter density Dark energy density Expansion rate of the universe Dark matter density Age of the universe NASA/WMAP science team