Cosmology : Cosmic Microwave Background & Large scale structure

Tarun SouradeepI.U.C.A.A.

Cosmology

IUCAA VSP program

(May 18-22, 2012)

Lec. 1:Background universe

Andromeda Galaxy

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

.102 30 Kg

The Realm of Cosmology100 millionLight years

The Realm of Cosmology500 millionLight years

The Realm of Cosmology5 Billion

Light years

The Realm of Cosmology

How can we even hope to

comprehend this immensely large&

complex Universe !?!Look for an

appropriate simple model

Modeling naturePicasso: Steiren series

Lick Observatory survey

North South

The Isotropic Universe Distribution of galaxies on the sky is broadly isotropic

Isotropy around every point implies

Homogeneity

Cosmological principle FLRW models

The Expanding Universe

Leads to the Hubble’s law

Recession velocity is Proportional to the distance

0 LH D v

Matter density: 1/VRadiation 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

Fig.: Ned Wright

Comoving spatial coordinates

Space-time of the cosmos

Fig.: Ned Wright

Comoving spatial coordinates

Conf

orm

al t

ime

Observer Distant galaxy

Equal time events at a distant galaxy

appears time-dilated

Cosmological Redshift

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 measurementsin 1929

Hubble’s law:Recession velocity of galaxies is proportional to the distance

0 LH D v

Fig.: Ned Wright

Frequency of light from a distant galaxy

Redshift, z=v/c

Redshift is related to distance

Expanding Universe

Hubble’s Law: Current

observationalstatus

Fig.: Ned Wright

Post-recombination :Freely propagating through (weakly perturbed) homogeneous & isotropic cosmos.

Pre-recombination : Tightly coupled to, and in thermal equilibrium with, ionized matter.

Pristine relic of a hot, dense & smooth early universe - Hot Big Bang model

(text background: W. Hu)

Cosmic Microwave Background

Cosmic “Super–IMAX” theater

Transparent universe

Opaque universe

43 Billion

Light-yearsHere & Now(14 Giga-years)

0.5 Mega-years

The Isotropic Universe

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”

Nobel prize 1978

Cosmic Microwave Background

The dominant radiation component in the universe

(D. Scott ’99)

~ 400 CMB photons per cubic cm.

Cosmic Microwave Background

“Dust” in an expanding box

Radiation in an expanding box

Size = ½ Number density x 8 Energy density x 16Temperature x 2

Size = ¼ Number density x 64Energy density x 128Temperature x 4

Size = ¼ Number density x 64Energy density x 64

Size = ½ Number density x 8 Energy density x 8

time

time

3

1L

4

1L

Matter density: 1/V

Radiation density: 1/(V L)Early Universe is

radiation dominated

E

The most perfect Black-Body spectrum in nature

COBE website

COBE –FIRAS

The CMB temperature –A single number

characterizes the radiation content of the universe!!

Cosmic Microwave Background

Baryons: Big Bang Nucleosynthesis

Baryons: Big Bang Nucleosynthesis

Flat Universe

Hyperbolic UniverseConstant negative curvature

Spherical UniverseConstant positive curvature

Geometry of the Universe

Friedman equations2

2 2 2

2 2 2

1 83

1 82

C

C

a Ga a R c

a G pa a R c

Ideal fluid: i i ip w

3 2

Ise

( )

ntropic expansion

cf.

(3 ) 0 ( ) (

) 0

d a p a

dE pdV Tdd V p dV

S

23(1 )

0

3(1 )0

(

)

iw

iwi i

ta tt

a

Evolution of density03

04

02

0

06

: Pressureless 'dust' ( 0)

1 : Relativistic (radiation) ( )3

1 : curvature "density" ( )3

: Vacuum energy ( 1)

: `stiff' matter ( 1)

mm i

rr i

KK i

V V i

SS i

wa

wa

wa

w

wa

`Standard’ cosmological model: Geometry, Expansion & Matter

Clustering matter

Non-Clustering matter

How much do we now know

about this model

Universe ?

lots !!!

NASA/WMAP science team

Age of the universe

Dark energy density

Dark matter density

Expansion rate of the

universe

Good old Cosmology, … New trend !Total energy density

Baryonic matter density