1. Cosmic Microwave Background radiation (CMB) 2. Akustische Peaks

Vorlesung 6+7

Roter Faden:

1. Cosmic Microwave Background radiation (CMB) 2. Akustische Peaks

3. Universum ist flach

4. Baryonic Acoustic Oscillations (BAO)

5. Energieinhalt des Universums

The oval shapes show a spherical surface, as in a global map. The global map. The whole sky can be thought of as the inside of a sphere.

Patches in the brightness are about 1 part in 100,000 = a bacterium on a

i

bowling ball = 60 meter waves on the surface

f th E th of the Earth.

Last Scattering Surface (LSS)

Temperatur-Fluktuationen = Dichtefluktuationen WMAP vs COBE

7

0.2

0.2

45 times sensitivity WMAP

ΔT/T 200 K/2 7K

WMAP

ΔT/T200uK/2.7K

Cosmology and the Cosmic Microwave Background

The Universe is approximately about 13.7 billion years old, according to the standard cosmological Big Bang model. At this time, it was a state of high

if i l h d d fill d i h l i l

uniformity, was extremely hot and dense was filled with elementary particles and was expanding very rapidly. About 380,000 years after the Big Bang, the energy of the photons had decreased and was not sufficient to ionise hydrogen

t Th ft th h t “d l d” f th th ti l d ld

atoms. Thereafter the photons “decoupled” from the other particles and could move through the Universe essentially unimpeded. The Universe has expanded and cooled ever since, leaving behind a remnant of its hot past, the Cosmic Microwave Background radiation (CMB) We observe this today as a 2 7 K Microwave Background radiation (CMB). We observe this today as a 2.7 K thermal blackbody radiation filling the entire Universe. Observations of the CMB give a unique and detailed information about the early Universe, thereby promoting cosmology to a precision science Indeed as will be discussed in

promoting cosmology to a precision science. Indeed, as will be discussed in more detail below, the CMB is probably the best recorded blackbody spectrum that exists. Removing a dipole anisotropy, most probably due our motion

through the Universe, the CMB is isotropic to about one part in 100,000. The through the Universe, the CMB is isotropic to about one part in 100,000. The 2006 Nobel Prize in physics highlights detailed observations of the CMB

performed with the COBE (COsmic Background Explorer) satellite.

From Nobel prize 2006 announcement

Early work

The discovery of the cosmic microwave background radiation has an y g

unusual and interesting history. The basic theories as well as the necessary experimental techniques were available long before the experimental

discovery in 1964 The theory of an expanding Universe was first given by discovery in 1964. The theory of an expanding Universe was first given by Friedmann (1922) and Lemaître (1927). An excellent account is given by Nobel laureate Steven Weinberg (1993).

Around 1960 a few years before the discovery two scenarios for the Around 1960, a few years before the discovery, two scenarios for the Universe were discussed. Was it expanding according to the Big Bang model, or was it in a steady state? Both models had their supporters and

h i i d i h l H Alf é (N b l i

among the scientists advocating the latter were Hannes Alfvén (Nobel prize in physics 1970), Fred Hoyle and Dennis Sciama. If the Big Bang model was the correct one, an imprint of the radiation dominated early Universe must still exist, and several groups were looking for it. This radiation must be thermal, i.e. of blackbody form, and isotropic.

From Nobel prize 2006 announcement

First observations of CMB

The discovery of the cosmic microwave background by Penzias and Wilson in 1964 (Penzias and Wilson 1965, Penzias 1979, Wilson 1979, Dicke et al. 1965) came as a complete surprise to them while they were trying to understand the source of

unexpected noise in their radio-receiver (they shared the 1978 Nobel prize in

physics for the discovery). The radiation produced unexpected noise in their radio receivers. Some 16 years earlier Alpher, Gamow and Herman (Alpher and Herman 1949, Gamow 1946), had predicted that there should be a relic radiation field

penetrating the Universe. It had been shown already in 1934 by Tolman (Tolman 1934) that the cooling blackbody radiation in an expanding Universe retains its

bl kb d f I h i h Al h G H d d i

blackbody form. It seems that neither Alpher, Gamow nor Herman succeeded in convincing experimentalists to use the characteristic blackbody form of the

radiation to find it. In 1964, however, Doroshkevich and Novikov (Doroshkevich

d N ik 1964) bli h d ti l h th li itl t d h f

and Novikov 1964) published an article where they explicitly suggested a search for the radiation focusing on its blackbody characteristics. One can note that some measurements as early as 1940 had found that a radiation field was necessary to explain energy level transitions in interstellar molecules (McKellar 1941) CN=Cyan explain energy level transitions in interstellar molecules (McKellar 1941).

Following the 1964 discovery of the CMB, many, but not all, of the steady state proponents gave up, accepting the hot Big Bang model. The early theoretical work is discussed by Alpher Herman and Gamow 1967 Penzias 1979 Wilkinson and

CN=Cyan

is discussed by Alpher, Herman and Gamow 1967, Penzias 1979, Wilkinson and Peebles 1983, Weinberg 1993, and Herman 1997.

Further observations of CMB

Following the 1964 discovery, several independent measurements of the

radiation were made by Wilkinson and others, using mostly balloon-borne, rocket-borne or ground based instruments The intensity of the radiation has rocket-borne or ground based instruments. The intensity of the radiation has its maximum for a wavelength of about 2 mm where the absorption in the atmosphere is strong. Although most results gave support to the blackbody form fe meas rements ere a ailable on the high freq enc (lo

form, few measurements were available on the high frequency (low

wavelength) side of the peak. Some measurements gave results that showed significant deviations from the blackbody form (Matsumoto et al. 1988).

The CMB was expected to be largely isotropic. However, in order to explain the large scale structures in the form of galaxies and clusters of galaxies

observed today, small anisotropies should exist. Gravitation can make small density fluctuations that are present in the early Universe grow and make galaxy formation possible. A very important and detailed general relativistic calculation by Sachs and Wolfe showed how three-dimensional density y y

fluctuations can give rise to two-dimensional large angle (> 1°) temperature anisotropies in the cosmic microwave background radiation (Sachs and

Wolfe 1967)

Wolfe 1967).

Dipol Anisotropy

Because the earth moves relative to the CMB, a dipole temperature

anisotropy of the level of

is expected This was observed in the anisotropy of the level of

is expected. This was observed in the 1970’s (Conklin 1969, Henry 1971, Corey and Wilkinson 1976 and Smoot, Gorenstein and Muller 1977). During the 1970-tis the anisotropies were

t d t b f th d f 10

10

b t t b d

expected to be of the order of 10

– 10

, but were not observed

experimentally. When dark matter was taken into account in the 1980-ties, the predicted level of the fluctuations was lowered to about 10

, thereby posing a great experimental challenge.

Explanation: two effects compensate the temperature anisotropies: p p p p DM dominates the gravitational potential after 

<< 

so hot spots in the grav. potential wells of DM have a higher temperature, but photons climbing out of the potential well get such a strong red shift that they are COLDER than the average temperature!

average temperature!

Because of e g atmospheric absorption it was long realized that

The COBE mission

Because of e.g. atmospheric absorption, it was long realized that measurements of the high frequency part of the CMB spectrum (wavelengths shorter than about 1 mm) should be performed from space A satellite instrument also gives full sky coverage and a long space. A satellite instrument also gives full sky coverage and a long observation time. The latter point is important for reducing systematic errors in the radiation measurements. A detailed account of

measurements of the CMB is given in a review by Weiss (1980).

measurements of the CMB is given in a review by Weiss (1980).

The COBE story begins in 1974 when NASA made an announcement of opportunity for small experiments in astronomy. Following lengthy discussions with NASA

Headquarters the COBE project was born and finally, on 18 November 1989,q p j y, , the COBE satellite was successfully launched into orbit. More than 1,000 scientists, engineers and administrators were involved in the mission. COBE carried three instruments covering the wavelength range 1 μm to 1 cm to measure the anisotropy and spectrum of the CMB as well as the diffuse infrared background radiation:

DIRBE (Diffuse InfraRed Background Experiment), DMR (Differential Microwave Radiometer) and FIRAS (Far InfraRed Absolute Spectrophotometer). COBE’s

mission was to measure the CMB over the entire sky, which was possible with the

chosen satellite orbit. All previous measurements from ground were done with limited sky coverage. John Mather was the COBE Principal Investigator and the project

l d f h H l ibl f h FIRAS i G

leader from the start. He was also responsible for the FIRAS instrument. George

Smoot was the DMR principal investigator and Mike Hauser was the DIRBE principal

The COBE mission

For DMR the objective was to search for anisotropies at three

l th 3 6 d 10 i th CMB ith

wavelengths, 3 mm, 6 mm, and 10 mm in the CMB with an angular resolution of about 7°. The anisotropies postulated to explain the large scale structures in the Universe should be explain the large scale structures in the Universe should be present between regions covering large angles. For FIRAS the objective was to measure the spectral distribution of the j p CMB in the range 0.1 – 10 mm and compare it with the

blackbody form expected in the Big Bang model, which is

diff t f th f t d f t li ht

different from, e.g., the forms expected from starlight or bremsstrahlung. For DIRBE, the objective was to measure the infrared background radiation The mission spacecraft the infrared background radiation. The mission, spacecraft and instruments are described in detail by Boggess et al.

1992. Figures 1 and 2 show the COBE orbit and the satellite,

respectively.

The COBE success

COBE was a success. All instruments worked very well and the results, in particular those from DMR , p and FIRAS, contributed significantly to make

cosmology a precision science. Predictions of the Big

B d l fi d

Bang model were confirmed: temperature

fluctuations of the order of 10

were found and the background radiation with a temperature of 2 725 K background radiation with a temperature of 2.725 K followed very precisely a blackbody spectrum.

DIRBE made important observations of the infrared p background. The announcement of the discovery of the anisotropies was met with great enthusiasm

ld id

worldwide.

CMB Anisotropies

The DMR instrument (Smoot et al. 1990) measured temperature

fluctuations of the order of 10^-5 for three CMB frequencies, 90, 53 and 31.5 GHz (wavelengths 3.3, 5.7 and 9.5 mm), chosen near the CMB 31.5 GHz (wavelengths 3.3, 5.7 and 9.5 mm), chosen near the CMB intensity maximum and where the galactic background was low. The angular resolution was about 7°. After a careful elimination of

instrumental background, the data showed a background contributiong , g from the Milky Way, the known dipole amplitudeΔT/T = 10^-3 probably caused by the Earth’s motion in the CMB, and a significant long sought after quadrupole amplitude, predicted in 1965 by Sachs and Wolfe. The first results were published in 1992.The data showed scale invariance for large angles, in agreement with predictions from inflation models.

Figure 5 shows the measured temperature fluctuations in galactic coordinates, a figure that has appeared in slightly different forms in many journals. The RMS cosmic

quadrupole amplitude was estimated at 13 ± 4 μK (ΔT/T = 5×10-6) with a systematic error of at most 3 μK (Smoot et al. 1992). The DMR anisotropies were compared and

f d i h d l f f i b W i h l 1992 Th f ll 4

found to agree with models of structure formation by Wright et al. 1992. The full 4 year DMR observations were published in 1996 (see Bennett et al. 1996). COBE’s results were soon confirmed by a number of balloon-borne experiments, and, more recently, by

th 1° l ti WMAP (Wilki Mi A i t P b ) t llit l h d

the 1° resolution WMAP (Wilkinson Microwave Anisotropy Probe) satellite, launched

Outlook

The 1964 discovery of the cosmic microwave background had a large impact on cosmology. The COBE results of 1992, giving strong support to the Big Bang model, gave a much more detailed view, and cosmology turned into a precision science. New ambitious experiments were started and the rate of publishing papers increased by an order of magnitude.

Our understanding of the evolution of the Universe rests on a number of observations,

i l di (b f COBE) th d k f th i ht k th d i f h d d

including (before COBE) the darkness of the night sky, the dominance of hydrogen and helium over heavier elements, the Hubble expansion and the existence of the CMB.

COBE’s observation of the blackbody form of the CMB and the associated small temperature fluctuations gave very strong support to the Big Bang model in proving temperature fluctuations gave very strong support to the Big Bang model in proving the cosmological origin of the CMB and finding the primordial seeds of the large structures observed today.

However while the basic notion of an expanding Universe is well established However, while the basic notion of an expanding Universe is well established, fundamental questions remain, especially about very early times, where a nearly exponential expansion, inflation, is proposed. This elegantly explains many

cosmological questions However there are other competing theories Inflation may cosmological questions. However, there are other competing theories. Inflation may have generated gravitational waves that in some cases could be detected indirectly by measuring the CMB polarization. Figure 8 shows the different stages in the evolution of the Universe according to the standard cosmological model. The first stages after the of the Universe according to the standard cosmological model. The first stages after the Big Bang are still speculations.

The colour of the universe

The young Universe was fantastically bright. Why? Because everywhere it was hot, and hot things glow brightly. Before we learned why this was:

collisions between charged particles create photons of light. As long as the g p p g g particles and photons can thoroughly interact then a thermal spectrum is produced: a broad range with a peak.

The thermal spectrum’s shape depends only on temperature: Hotter objects The thermal spectrum’s shape depends only on temperature: Hotter objects appear bluer: the peak shifts to shorter wavelengths, with: pk = 0.0029/TK m = 2.910⁶/T nm. At 10,000K we have peak = 290 nm (blue), while at 3000K we have peak = 1000 nm (deep orange/red).p ( p g )

Let’s now follow through the color of the Universe during its first million years. As the Universe cools, the thermal spectrum shifts from blue to red, spending 80 000 years in each rainbow color

spending ~80,000 years in each rainbow color.

At 50 kyr, the sky is blue! At 120 kyr it’s green; at 400 kyr it’s orange; and by 1 Myr it’s crimson. This is a wonderful quality of the young Universe: it paints its sky with a human palette.

Quantitatively: since peak ~ 310⁶/T nm, and T ~ 3/S K, then peak ~ 10⁶ / S nm. Notice that today, S = 1 and so peak = 10⁶ nm = 1 mm, which is, of course the peak of the CMB microwave spectrum

course, the peak of the CMB microwave spectrum.

Hotter objects appear brighter. There are two reasons for this:

Light Intensity

Hotter objects appear brighter. There are two reasons for this:

More violent particle collisions make more energetic photons. Converting pk ~ 0.003/T m to the equivalent energy units, it turns out that in a thermal spectrum, the average photon energyis ~ kT. So, for systems in thermal equilibrium, the

i l h i kT F i l llid

mean energy per particle or per photon is ~kT. Faster particles collide more frequently, so make more photons. In fact the number density of photons, nph  T³. Combining these, we find that the intensity of thermal radiation increases dramatically with temperature Itot = 2.210^-7T⁴ Watt /m² inside a gas at

dramatically with temperature Itot 2.2 10 T Watt /m inside a gas at temperature T.

At high temperatures, thermal radiation has awesome power – the multitude of particle collisions is incredibly efficient at creating photons. To help feel this, consider the light

f lli f ti 1400 W tt/ ² h t f l b d it

falling on you from a noontime sun – 1400 Watt/m² – enough to feel sunburned quite quickly. Let’s write this as Isun.

Float in outer space, exposed only to the CMB, and you experience a radiation field of I_3K3K = 2.210^-72.7⁴ = 10 W/m ² = 10^-8 Isun – not much! Here on Earth at 300K we have I_300K ~ 1.8 kW/m² (fortunately, our body temperature is 309K so you radiate 2.0 kW/m², and don’t quickly boil!). A blast furnace at 1500 C (~1800K) has I_1800K = 2.3 MW/m² = 1600 Isun (you boil away in ~1 minute).

At th ti f th CMB (380 k ) th di ti i t it I 17 MW/ ² At the time of the CMB (380 kyr), the radiation intensity was I_3000K= 17 MW/m²

= 12,000 Isun – you evaporate in 10 seconds.

In the Sun’s atmosphere, we have I_5800K= 250 MW/m² = 210,000 Isun. That’s a major city’s power usage, falling on each square meter.j y p g , g q

Radiation in the Sun’s 14 million K core has: I = 810²¹W/m² ~ 10¹⁹ Isun (you boil away in much less than a nano-second).

Rotationally excited CN

The first observations of the CMB were made by McKellar using interstellar molecules in 1940. The image at right shows a

f h O h k i 1940 hi h h h k

spectrum of the star zeta Oph taken in 1940 which shows the weak R(1) line from rotationally excited CN. The significance of these data was not realized at the time and there is even a line in the data was not realized at the time, and there is even a line in the 1950 book Spectra of Diatomic Molecules by the Nobel-prize winning physicist Gerhard Herzberg, noting the 2.3 K rotational g p y g g temperature of the cyanogen molecule (CN) in interstellar space but stating that it had "only a very restricted meaning." We now k th t thi l l i i il it d b th CMB i l i know that this molecule is primarily excited by the CMB implying a brightness temperature of T

= 2.729 +/- 0.027 K at a wavelength of 2 64 mm ( Roth Meyer & Hawkins 1993)

of 2.64 mm ( Roth, Meyer & Hawkins 1993).

http://www.astro.ucla.edu/~wright/CMB.htmlp g

Warum ist die CMB so wichtig in der Kosmologie?

) Di CMB b i d d U i f üh h iß

a) Die CMB beweist, dass das Universum früher heiß war und das die Temperaturentwicklung verstanden ist

b) Alle Wellenlängen ab einer bestimmten Länge (=oberhalb den akustischen Wellenlängen) kommen alle

gleich stark vor, wie von der Inflation vorhergesagt.

c) Kleine Wellenlängen (akustische Wellen) zeigen c) Kleine Wellenlängen (akustische Wellen) zeigen

ein sehr spezifisches Leistungsspektrum der akustischen Wellen im frühen Universum, woraus man ,

schließen kann, dass das Universum FLACH ist und

die baryonische Dichte nur 4-5% der Gesamtdichte ausmacht.

Warum akustische Wellen im frühen Universum?

Definiere: δ=Δρ/ρ ρ ρ ^{F=ma P}

Newton: F=ma oder a-F/m=0

δ``+ (Druck Gravitationpotential) δ=0

F

Lösung:

δ + (Druck-Gravitationpotential) δ=0

Lösung:

Druck gering: δ=ae

,

d.h. exponentielle Zunahme von

( >G it ti k ll ) (->Gravitationskollaps) Druck groß: δ=ae

, d.h. Oszillation von

(akustische Welle)

Rücktreibende Kraft: Gravitation

Rücktreibende Kraft: Gravitation

Antreibende Kraft: Photonendruck

Ph t El kt B g d t k K l g

Mathematisches Modell

• Photonen, Elektronen, Baryonen wegen der starken Kopplung wie eine Flüssigkeit behandelt → ρ, v, p

• Dunkle Materie dominiert das durch die Dichtefluktuationen Dunkle Materie dominiert das durch die Dichtefluktuationen hervorgerufene Gravitationspotential Φ

• δρ/δt+(ρv)=0

( i i l i h h l ))

(Kontinuitätsgleichung = Masse-Erhaltung))

• v+(v·)v = -(Φ+p/ρ)

(E l Gl i h I l h lt ) (Euler Gleichung = Impulserhaltung)

• ² Φ = 4πGρ

(Poissongleichung = klassische Gravitation)

Tiefe des Potentialtopfs be- stimmt durch dunkle Materie

(Poissongleichung = klassische Gravitation)

• erst nach Überholen durch den akustischen Horizont H_s= c_sH^-1 , (c_s = Schallgeschwindigkeit) können die ersten beiden (c_s Schallgeschwindigkeit) können die ersten beiden Gleichungen verwendet werden

• Lösung kann numerisch oder mit Vereinfachungen analytisch

b ti t d d t i ht b i dä ft

bestimmt werden und entspricht grob einem gedämpftem harmonischen Oszillator mit einer antreibenden Kraft

Entwicklung der Dichtefluktuationen im Universum

Man kann die Dichtefluktuationen

im frühen Univ. als Temp.-Fluktuationen

im frühen Univ. als Temp. Fluktuationen

der CMB beobachten!

The first sound waves The first sound waves

compression

dim dim

a) gas falls into valleys, gets compressed, & glows brighter

rarefaction rarefaction

compression dim

bright

i i i i

rarefaction bright

bright

b) it overshoots, then rebounds out, is rarefied, & gets dimmer

) it th f ll b k i i t k d i

compression compression

dim

c) it then falls back in again to make a second compression





the oscillation continues the oscillation continues

sound waves are created sound waves are created

•

Gravity drives the growth of sound in the early Universe.

•

The gas must also feel pressure, so it rebounds out of the valleys.

•

We see the bright/dim regions as patchiness on the

.

Akustische Peaks

1. akust. Peak

t=t _rec

t=1/2t _rec t=1/2t _rec

2 akust Peak 2. akust. Peak

1/3

t=1/3t _rec 3. akust. Peak

Akustische Wellen im frühen Universum

Ü

Überdichten am Anfang: Inflation

Druck der akust. Welle und Gravitation verstärken die Temperaturschwankungen in der Grundwelle (im ersten Peak)

http://astron.berkeley.edu/~mwhite/sciam03 short.pdfp y _ p

Druck der akust. Welle und Gravitation wirken

gegeneinander in der Oberwelle ( im zweiten Peak)

Mark Whittle Mark Whittle

University of Virginia University of Virginia y y g g

http://www.astro.virginia.edu/~dmw8f http://www.astro.virginia.edu/~dmw8f

See also: “full presentation”

See also: “full presentation”

Viele Plots und sounds von Whittles Webseite

Akustische Wellen im frühen Universum

Flute power spectra

Bь Clarinet

piano range

Modern Flute

Überdichten am Anfang: Inflation

Sky Maps  Power Spectra

peak

We “see” the CMB sound We “see” the CMB sound as

as waves on the sky waves on the sky. .

trough

Use special methods Use special methods to measure the

to measure the strength strength to measure the

to measure the strength strength of each wavelength.

of each wavelength.

Shorter wavelengths Shorter wavelengths are smaller frequencies are smaller frequencies

hi h it h hi h it h are higher pitches are higher pitches

Lineweaver 1997

Sound waves in the sky Sound waves in the sky

This slide illustrates the situation. Imagine looking down on the ocean from a plane and seeing far below, surface waves. The patches on the

i b k d k d t h f di t t d

Water waves Water waves ::

microwave background are peaks and troughs of distant sound waves.

Water waves Water waves ::

high/low level of high/low level of water surface

water surface

many waves of different many waves of different sizes directions & phases sizes directions & phases sizes, directions & phases sizes, directions & phases

all “superimposed”

all “superimposed”

Sound waves Sound waves ::

red/blue = high/low red/blue = high/low

& li ht

& li ht

gas & light pressure

gas & light pressure

Power (Leistung) pro Wellenlänge)

This distribution has a lot of long wavelength power and a little short a elength po er

and a little short wavelength power

Sound in space !?!

Sound in space !?!

• Surely, the vacuum of “space” must be silent silent ?

 N f h U i

 Not for the young Universe:

• Shortly after the big bang ( eg @ CMB: 380 000 rs )

• Shortly after the big bang ( eg @ CMB: 380,000 yrs )

• all matter is spread out evenly spread out evenly (no stars or galaxies yet)

• Universe is smaller Universe is smaller smaller smaller   everything closer together (by ×1000) everything closer together (by 1000)

• the density is much higher density is much higher (by ×10

= a billion)

• 7 trillion photons & 7000 protons/electrons per cubic inch

• all at 5400ºF with pressure 10

(ten millionth) Earth’s atm.



 There is a hot thin atmosphere for sound waves There is a hot thin atmosphere for sound waves



 There is a hot thin atmosphere for sound waves There is a hot thin atmosphere for sound waves

• unusual fluid  intimate mix of gas & light

d d f li h

• sound waves propagate at ~50% speed of light

Big Bang Akustik

http://astsun.astro.virginia.edu/~dmw8f/teachco/

While the universe was still foggy, atomic matter was trapped by light's pressure and prevented from clumping up. In fact, this high-pressure gas of light and atomic matter responds to the pull of gravity like air responds in an organ pipe – it

bounces in and out to make sound waves This half million bounces in and out to make sound waves. This half-million year acoustic era is a truly remarkable and useful period of cosmic history. To understand it better, we'll discuss the y , sound's pitch, volume, and spectral form, and explain how these sound waves are visible as faint patches on the Cosmic Microwave Background. Perhaps most bizarre: analyzing the CMB patchiness reveals in the primordial sound a

fundamental and harmonics the young Universe behaves

fundamental and harmonics – the young Universe behaves

like a musical instrument! We will, of course, hear acoustic

versions, suitably modified for human ears. , y

Akustik Ära

Since it is light which provides the pressure, the speed of pressure waves (sound) is

waves (sound) is incredibly fast: vs ~ 0.6c! This makes sense: the gas is incredibly lightweight compared to its pressure, so the pressure force moves the gas very easily. Equivalently, the photon speeds are, of

h

course, c – hence vs ~ c.

In summary: we have an extremely lightweight foggy gas of brilliant light and a trace of particles, all behaving as a single fluid with modest pressure and very high sound speed. With light dominating the

pressure, the primordial sound waves can also be thought of as great

p , p g g

surges in light’s brilliance.

After recombination photons and particles decouple; the After recombination, photons and particles decouple; the pressure drops by 10

and sound ceases. The acoustic era only lasts 400 kyr, and is then over.

only lasts 400 kyr, and is then over.

Where the sound comes from?

A too-quick answer might be: “of course there’s sound, it was a “big bang”

after all, and the explosion must have been very loud”. This is completely

an explosion into an atmosphere; it was an expansion of space itself. The Hubble law tells us that every point recedes from every other – there is no compression – no sound. Paradoxically, the big bang was totally silent!

How, then, does sound get started? Later we’ll learn that although the

Universe was born silent, it was also born very slightly lumpy. On all scales, from tiny to gargantuan there are slight variations in density randomly from tiny to gargantuan, there are slight variations in density, randomly scattered, everywhere – a 3D mottle of slight peaks and troughs in density.

We’ll learn how this roughness grows over time, but for now just accept

this framework The most important component for generating sound is

this framework. The most important component for generating sound is

dominates the density, so it determines the gravitational landscape.

Where the sound comes from?

Everywhere, the photon-baryon gas feels the pull of dark matter.

How does it respond? It begins to “fall” towards the over-dense regions, and away from the under-dense regions. Soon, however, its regions, and away from the under dense regions. Soon, however, its pressure is higher in the over-dense regions and this halts and

reverses

the motion; pushing the gas back out. This time it

overshoots only to turn around and fall back in again The cycle overshoots, only to turn around and fall back in again. The cycle repeats, and we have a sound wave!

The situation resembles a spherical organ pipe: gas bounces in and

t f hl h i l i [O t “f lli i ” d

out of a roughly spherical region. [One caveat: “falling in” and

“bouncing out” of the regions is only relative to the overall expansion, which continues throughout the acoustic era.]

Notice there is a quite different behavior between dark matter and

the photon-baryon gas. Because the dark matter has no pressure (it

interacts with nothing, not even itself), it is free to clump up under g ) p p

its own gravity. In contrast, the photon-baryon gas has pressure,

which tries to keep it uniform (like air in a room). However, in the

lumpy gravitational field of dark matter, it falls and bounces this

lumpy gravitational field of dark matter, it falls and bounces this

way and that in a continuing oscillation.

How does sound get to us ? How does sound get to us ?

Consider listening to a concert on the radio:

Bow+string microphone

& amplifier

& antenna

ariel &

amplifier speakers sound

sound

radio waves radio waves

your your ears

& antenna speakers

ears ears ears

Concert hall

Concert hall

Listener Listener Concert hall

Concert hall

Listener Listener

few µsec delay sound

gravity + hills/valleys

waves glow

glow telescope

computer speakers sound

sound

light light

your your

ears

microwaves ears

microwaves

Big Bang

Big Bang

Listener Listener Big Bang

Big Bang

Listener Listener

The Big Bang is all around us !

Since looking in any any direction looks back to the foggy wall

 we see the wall in all all directions.

 the entire entire sky sky glows with microwaves

 h fl h f h Bi B i ll ll dd !

 the flash from the Big Bang is all all around around us us!

Akustische Peaks von WMAP

Ort-Zeit Diagramm

CMB Sound Spectrum

Click for sound

acoustic

non-acoustic

3eaver 2003

220 HzA

Linewe

Frequency (in Hz)

Kugelflächenfunktionen

l=4

l=8

J d F kti k i th l l 12

Jede Funktion kann in orthogonale

Kugelflächenfkt. entwickelt werden. Große Werte von l beschreiben Korrelationen unter

l=12

kleinen Winkel.

Vom Bild zum Powerspektrum

• Temperaturverteilung ist Funktion auf Sphäre:

ΔT(θ,φ) bzw. ΔT(n) = ΔΘ(n)( ,φ) ( ) ( ) T T

n=(sinθcosφ,sinθsinφ,cosθ)

• Autokorrelationsfunktion:

C(θ)=<ΔΘ(n )·ΔΘ(n )> ^{n n} C(θ)=<ΔΘ(n₁)·ΔΘ(n₂)>_|n1-n2|

=(4π)^-1 Σ^∞_l=0 (2l+1)C_lP_l(cosθ)

• PP_ll sind die Legendrepolynome: sind die Legendrepolynome:

P_l(cosθ) = 2^-l·d^l/d(cos θ)^l(cos²θ-1)^l.

• Die Koeffizienten C_l bilden das Powerspektrum von ΔΘ(n).

mit cosθ=n1·n2 mit cosθ=n1·n2

Temperaturschwankungen als Fkt. des Öffnungswinkels

Θ  180/l

Balloon exp.

Das Leistungsspektrum (power spectrum)

Ursachen für Temperatur Schwankungen:

Schwankungen:

Große Skalen:

Gravitationspotentiale Kleine Skalen:

Akustische Wellen

Position des ersten Peaks

Berechnung der Winkel, worunter man die maximale Temperaturschwankungen der Grundwelle beobachtet:

Raum-Zeit x

t Inflation

der Grundwelle beobachtet:

Maximale Ausdehnung einer akust. Welle zum Zeitpunkt trec: c * trec (1+z)

t

Entkopplung

zum Zeitpunkt trec: c

* trec (1+z) Beobachtung nach t

=13.8 10

yr.

Öffnungswinkel θ = c

* t

* (1+z) / c*t

Mit (1+ ) 3000/2 7 1100 d

Mit (1+z)= 3000/2.7 =1100 und

trec = 3,8 10

yr und Schallgeschwindigkeit c

=c/3 für ein relativ. Plasma folgt:

max. T / T

θ

= 0.0175 = 1

(plus (kleine) ART Korrekt.)

Beachte: c

≡ dp/d = c

/3, da p= 1/3 c

max. T / T

unter 1

nλ/2=c

t

Präzisere Berechnung des ersten Peaks

Vor Entkopplung Universum teilweise strahlungsdominiert.

Hier ist die Expansion  t

statt t

in materiedominiertes Univ Hier ist die Expansion  t

statt t

in materiedominiertes Univ.

Muss Abstände nach bewährtem Rezept berechnen:

Erst mitbewegende Koor. und dann x S(t)

Abstand < t

: S(t) c d = S(t) c dt/S(t) = 2ct

für S  t

 

Abstand > t

: S(t) c d =S(t)c dt/S(t) = 3ct

für S  t

Winkel θ = 2 * c * t * (1+z) / 3*c*t

= 0 7 Grad

Winkel θ 2 c

t

(1+z) / 3 c t

0.7 Grad

Auch nicht ganz korrekt, denn Univ. strahlungsdom. bis t=50000 a,

nicht 380000 a. Richtige Antwort: Winkel θ = 0.8 Grad oder l=180/0.8=220 nicht 380000 a. Richtige Antwort: Winkel θ 0.8 Grad oder l 180/0.8 220

Temperaturanisotropie der CMB

Position des ersten akustischen Peaks bestimmt

Krümmung des Universums!

Present and projected Results from CMB

180 /l

 

See Wayne Hu's WWW-page:

http://background.uchicago.edu/~whu 180 /l

 

Verhältnis peak1/peak2->

Verhältnis peak1/peak2->

Baryondichte

Position erster Peak->

Flaches Univ.

Flaches Univ.

Geometry of the Universe Geometry of the Universe

Open : Ω= 0.8 Flat : Ω= 1.0 Closed: Ω=1.2

L i h High pitch

Low pitch High pitch

Long wavelength Short wavelength

Atomic content of the Universe Atomic content of the Universe

2% atoms 4% atoms 8% atoms

Low pitch High pitch

Low pitch High pitch

WMAP analyzer tool

http://wmap.gsfc.nasa.gov/resources/camb_tool/index.html

Conformal Space-Time (winkel-erhaltende Raum-Zeit)

Raum-Zeit x

t t

x

 = x/S(t) = x(1+z) t

  = t / S(t) = t (1+z)



conformal=winkelerhaltend



http://arxiv.org/PS_cache/arxiv/pdf/0803/0803.0732v2.pdf Neueste WMAP Daten (2008)

Polarisation Polarisation

Reionisation nach 2.10

a

Temperatur p

Temperatur- und Polarisationsanisotropien um 90 Grad in Phase verschoben, Temperatur und Polarisationsanisotropien um 90 Grad in Phase verschoben, weil Polarisation Fluss der Elektronen, also wenn x  cos (t), dann v  sin (t)

Neueste WMAP Daten (2008)

CMB polarisiert durch Streuung an Elektronen (Thomson Streuung)

K E k l

Kurz vor Entkoppelung:

Streuung der CMB Photonen.

Nachher nicht mehr da mittlere Nachher nicht mehr, da mittlere freie Weglange zu groß.

Lange vor der Entkopplung: g pp g Polarisation durch Mittelung über viele Stöße verloren.

Nach Reionisation der Baryonen durch Sternentstehung wieder durch Sternentstehung wieder

Streuung.

Erwarte Polarisation also kurz nach dem akust. Peak (l = 300)

d f ß Ab tä d (l < 10) und auf großen Abständen (l < 10)

Instruktiv:http://background.uchicago.edu/~whu/polar/webversion/node1.htm

Entwicklung des Universums

Polarisation durch Thomson Streuung

(elastische Photon-Electron Streuung)

CMB Polarisation durch Thomson Streuung (elastische Photon-Electron Streuung)

Prinzip: unpolarisiertes Photon unter 90 Grad gestreut, muss immer

noch E-Feld  Richtung haben, so eine Komponente verschwindet! g , p

Daher bei Isotropie keine Pol. , bei Dipol auch nicht, nur bei Quadr.

CMB Polarisation bei Quadrupole-Anisotropie

Polarization entweder radial oder tangential um hot oder cold spots (proportional zum Fluss der Elektronen, also zeigt wie Plasma sich bewegte bei z=1100 and auf große Skalen wie Plasma in Galaxien Cluster sich relativ zum CMB bewegt)

http://gyudon.as.utexas.edu/~komatsu/presentation/wmap7_ias.pdf

CMB Polarisation bei Quadrupole-Anisotropie

Woher kennt man diese Verteilung?

If it is not dark,

it does not matter

Erste Evidenz für Vakuumenergie

SNIa compared with Porsche rolling up a hill

SNIa data very similar to a dark Porsche rolling up a hill and reading speedometer regularly, i.e. determining v(t), which can regularly, i.e. determining v(t), which can be used to reconstruct x(t) =∫v(t)dt.

(speed  distance, for universe Hubble law) This distance can be compared laterp

with distance as determined from the luminosity of lamp posts (assuming same brightness for all lamp posts)p p

(luminosity  distance, if SN1a treated as

‘standard’ candles with known luminosity)

f h f l f h

If the very first lamp posts are further away than expected, the conclusion must be that the Porsche instead of rolling up the hill d it i i ddi i l

hill used its engine, i.e. additional

acceleration instead of decelaration only.

(universe has additional acceleration (by dark ) i t d f d l ti l )

energy) instead of decelaration only)

Perlmutter 2003 Perlmutter 2003

Abstand Abstand

Zeit

Vergleich mit den SN 1a Daten

SN1a empfindlich für Beschleunigung, d.h. g g,



- 

_

CMB empfindlich für totale Dichte d.h.



+ 

( )

= (_SM+ _DM)

Akustische Baryon Oszillationen I:

http://cmb.as.arizona.edu/~eisenste/acousticpeak/acoustic_physics.html

Let's consider what happens to a point- like initial perturbation. In other words, we're going to take a little patch of space we're going to take a little patch of space and make it a little denser. Of course, the universe has many such patchs, some overdense some underdense We're just overdense, some underdense. We re just going to focus on one. Because the fluctuations are so small, the effects of many regions just sum linearly.

many regions just sum linearly.

The relevant components of the universe are the dark matter, the gas (nuclei and electrons), the cosmic microwave e ec o s), e cos c c ow ve background photons, and the cosmic background neutrinos.

Akustische Baryon Oszillationen II:

http://cmb.as.arizona.edu/~eisenste/acousticpeak/acoustic_physics.html

Now what happens?

The neutrinos don't interact with anything and are too fast to be bound gravitationally, so they begin to stream away from the initial perturbation

from the initial perturbation.

The dark matter moves only in response to gravity and has no intrinsic motion (it's cold dark matter). So it sits still.

The perturbation (now dominated by the photons and neutrinos) is overdense, so it attracts the surroundings, causing more dark matter to fall towards the center.

The gas, however, is so hot at this time that it is ionized. In the resulting plasma the cosmic microwave background the resulting plasma, the cosmic microwave background photons are not able to propagate very far before they scatter off an electron. Effectively, the gas ^and photons are locked into a single fluid. The photons are so hot and numerous, that this combined fluid has an enormous pressure relative to its density. The initial overdensity is therefore also an initial overpressure. This pressure tries to equalize itself with the surroundings, but this simply The result is that the perturbation in

th d h t i i d t d to equalize itself with the surroundings, but this simply results in an expanding spherical sound wave. This is just like a drum head pushing a sound wave into the air, but the speed of sound at this early time is 57% of the speed of the gas and photon is carried outward:

light!

Akustische Baryon Oszillationen III:

http://cmb.as.arizona.edu/~eisenste/acousticpeak/acoustic_physics.html

As time goes on, the spherical shell of gas and photons continues to expand. The neutrinos spread out. The dark matter collects in the overall density perturbation, which is now considerably bigger because

th h t d t i h l ft th

the photons and neutrinos have left the center. Hence, the peak in the dark matter remains centrally concentrated but with an increasing width This is generating the increasing width. This is generating the familiar turnover in the cold dark matter power spectrum.

Where is the extra dark matter at large Where is the extra dark matter at large radius coming from? The gravitational forces are attracting the background material in that region, causing it to contract material in that region, causing it to contract a bit and become overdense relative to the background further away

Akustische Baryon Oszillationen IV:

http://cmb.as.arizona.edu/~eisenste/acousticpeak/acoustic_physics.html The expanding universe is cooling.

Around 400,000 years, the temperature is low enough that the temperature is low enough that the electrons and nuclei begin to combine into neutral atoms. The photons do not scatter efficiently off of neutral not scatter efficiently off of neutral atoms, so the photons begin to slip past the gas particles. This is known Silk d i (A J 151 459 1968) as Silk damping (ApJ, 151, 459, 1968).

The sound speed begins to drop

because of the reduced coupling

between the photons and gas and

because the cooler photons are no

longer very heavy compared to the g y y p

gas. Hence, the pressure wave slows

down.

Akustische Baryon Oszillationen V:

http://cmb.as.arizona.edu/~eisenste/acousticpeak/acoustic_physics.html

This continues until the photons have l t l l k d t f th

completely leaked out of the gas perturbation. The photon perturbation begins to smooth itself out at the speed of light (just like the neutrinos did) of light (just like the neutrinos did).

The photons travel (mostly) unimpeded until the present-day, where we can record them as the where we can record them as the microwave background (see below).

At this point, the sound speed in the gas has dropped to much less than the gas has dropped to much less than the speed of light, so the pressure wave stalls.

Akustische Baryon Oszillationen VI:

http://cmb.as.arizona.edu/~eisenste/acousticpeak/acoustic_physics.html

We are left with a dark matter perturbation around the original center and a gas perturbation in a shell about 150 Mpc (500 million light-

) i di years) in radius.

As time goes on, however, these two species gravitationally attract each

th Th t b ti b i t i

other. The perturbations begin to mix together. More precisely, both perturbations are growing quickly in response to the combined gravitational response to the combined gravitational forces of both the dark matter and the gas. At late times, the initial differences are small compared to the differences are small compared to the later growth.

Akustische Baryon Oszillationen VII:

http://cmb.as.arizona.edu/~eisenste/acousticpeak/acoustic_physics.html

Eventually, the two look quite similar. The spherical shell of the gas perturbation has imprinted itself in the dark matter. This is known as the acoustic peak.

The acoustic peak decreases in

contrast as the gas come into lock-

contrast as the gas come into lock

step with the dark matter simply

because the dark matter, which has

no peak initially outweighs the gas

no peak initially, outweighs the gas

5 to 1.

Akustische Baryon Oszillationen VIII:

http://cmb.as.arizona.edu/~eisenste/acousticpeak/acoustic_physics.html

At late times, galaxies form in the regions that are overdense in gas and dark matter. For the most part, this is dark matter. For the most part, this is driven by where the initial overdensities were, since we see that the dark matter has clustered heavily

d e s c us e ed e v y

around these initial locations. However, there is a 1% enhancement in the regions 150 Mpc away from theseg p y initial overdensities. Hence, there should be an small excess of galaxies 150 Mpc away from other galaxies, as opposed to 120 or 180 Mpc. We can see this as a single acoustic peak in the correlation function of galaxies.

B f h b l i h fil Alternatively, if one is working with the power spectrum statistic, then one sees the effect as a series of acoustic

ill i

Before we have been plotting the mass profile (density times radius squared). The density profile is much steeper, so that the peak at 150 Mpc is much less than 1% of the density near

oscillations.

Mpc is much less than 1% of the density near the center.

One little telltale bump !!

A small excess in correlation at 150 Mpc.!

1 2

( ) r ( ) ( ) r r

     

p SDSS survey

(astro ph/0501171) (astro-ph/0501171)

(Einsentein et al. 2005)

150 Mpc.

150 Mpc =2c t

akustischer Horizont

150 Mpc =2c

t

akustischer Horizont

Akustische Baryonosz. in Korrelationsfkt. der Dichteschwankungen der Materie!

150 Mpc.

105 h

¼ 150

The same CMB oscillations at low redshifts !!!

SDSS surveyy

(astro-ph/0501171) (Einsentein et al. 2005)

( )

Combined results

http://arxiv.org/PS cache/arxiv/pdf/0804/0804.4142v1.pdf

http://nedwww.ipac.caltech.edu/level5/March08/Frieman/Frieman4.html

p g _ p p