april 17, 2001lynn cominsky - cosmology a3501 answer to last week’s question how do we know that...

April 17, 2001 Lynn Cominsky - Cosmology A350

1

Answer to last week’s Question

How do we know that the Milky Way is at the outer edge of the Virgo cluster?

A) We can see the center of the Virgo cluster

B) We can measure our velocity with respect to the Virgo cluster and we are heading towards it

C) We can measure our velocity with respect to the Virgo cluster and we are heading away from it

D) We can see the edges of the cluster

B


2

Group 10

Brian Berryessa

Charity Haas

Andrew McFarland

Jessica Rapin

John Wilczak?


3

Group 10


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Background RadiationLecture 10


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Big Bang Timeline

We are hereToday’s lecture


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Cosmic Microwave Background

Discovered in 1965 by Arno Penzias and Robert Wilson who were working at Bell Labs

Clinched the hot big bang theory

Excess noise in horned antennae was not due to pigeon dung!


7

Where is the CMBR?Map of redshift vs. time after Big Bang

CMBR

Z=1000

Universe has expanded and cooled

down by 1+z (about 1000)

since the photons last scattered off the CMBR


8

CMBR

Photons in CMBR come from surface of last scattering – where they stop interacting with matter and travel freely through spaceCMBR photons emanate from a cosmic photosphere – like the surface of the Sun – except that we inside it looking outThe cosmic photosphere has a temperature which characterizes the radiation that is emitted It has cooled since it was formed by more than 1000 to 2.73 degrees K


9

COBE launch movie

COsmic Background Explorer Launched 11/18/89 into polar orbit


10

COBE

3 instruments: FIRAS, DMR and DIRBE

Cryogens ran out on 9/ 21/ 90 ending observations by FIRAS and longer wavelengths of DIRBE

DMR and the shorter wavelengths of DIRBE operated until 11/23/93


11

COBE data/DIRBE

Diffuse InfraRed Background Experiment

IR background is produced by dust warmed by all the stars that have existed since the beginning of time

Limit to energy produced by all stars in the Universe


12

COBE data/FIRAS

Far InfraRed Absolute Spectrophotometer


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COBE data/FIRAS

FIRAS results show that 99.994% of the radiant energy of the Universe was released within the first year after the Big Bang

Data match the Big Bang predictions so exactly that the error bars are within the curve itself

Residuals from a 2.728 (+/- 0.004)

degree Kelvin blackbody


14

COBE data/FIRAS

The CMBR is described by the most perfect blackbody spectrum ever measured Blackbody spectra are produced when material is thick and dense, so that photons must scatter many times before they escapeThe photons must therefore have been emitted from dark, thick matter at a much earlier timeThe CMBR energy was emitted when the Universe was 106 times smaller and hotter than it is now. Photons continued to scatter until the Universe was 10-3 its present size


15

COBE DMR

Differential Microwave Radiometer 3 different wavelengths 2 antennae for each wavelength, 7 degree beam Pointed 60 degrees apart

DMR work featured in George Smoot’s “Wrinkles in Time”


16

COBE data/DMR

Dipole due to movement of Solar System

warm

cool


17

COBE data/DMR

Dipole removed to show “wrinkles”


18

COBE data/DMR

Fluctuations in CMB seen by DMR are at the level of one part in 100,000

Blue spots mean greater density

Red spots mean lesser density

(in the early Universe)


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CMBR Fluctuations

COBE measures the angular fluctuations on large scales, down to about L=16


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CMBR Fluctuations

Determining the spectrum of fluctuations in the CMBR can directly differentiate between models of the Universe

Angular size of

fluctuation

How much power there is


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CMBR Fluctuations

Current data favor a peak near LEff = 210 This is consistent with the sCDM (standard Cold Dark Matter) and CDM models (CDM + cosmological constant)Both describe a flat (=1) Universe


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CMBR Fluctuations

For a given model (e.g., sCDM) the fluctuation spectrum can also be used to directly determine the Hubble constant


23

BOOMERanG

Balloon Observations Of Millimeter Extragalactic Radiation and Geophysics

12 - 20 arc min resolution – about 35 times better than COBE

Two flights: 1998/99 (10 days) and 1999/00

Sensitive to temperature differences as small as 0.0001 degrees C

Imaged 2.5% of entire sky


24

BOOMERanG

Photos from 1998 flight in

Antarctica


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BOOMERanG vs. COBE

1800 square degrees of sky

-300K +300 K

moon


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BOOMERanG 1998 Data

What the fluctuations would look like to scale on the real sky above the BOOMERanG balloon launch facilities


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BOOMERanG 1998 Data

What the fluctuations would look like for open, flat and closed universe modelsClosed: larger structures Open: smaller structures


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BOOMERanG 1998 Data

Peak at 1o indicates presence of both baryonic and non-baryonic matter

Second peak tells you how much of each


29

BOOMERanG vs. Supernovae

Flat universe is best fit to BOOMERanG data

Overlap with supernova data indicates cosmological constant > 0

matter


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MAXIMA

Millimeter Anisotrop eXperiment IMaging Array – launched 6/15/99


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MAXIMA

10 arc minute resolution

150 GHz and 240 GHz

15,000 pixels

Smoothed image


32

BOOMERanG and MAXIMA Results

0.85< tot<1.25

Supports cosmological constant =0.6

(accelerating Universe), since M is only about 0.2-0.4 (including dark matter)


33

X-ray Background

Discovered over 35 years ago in rocket flights Early theories explained the X-ray background

as a diffuse, hot gas which filled the Universe Data from Einstein Observatory showed about

50% of the background could be due to quasars ROSAT data explained about 60% of the 1-2

keV X-ray background with quasars However flux and energy spectra did not add

up correctly if the background was all quasars


34

X-ray Background

ROSAT 0.75 keV map

Shows smooth blue background plus bright superbubble ring at D=150 pc with R= ~100 pc


35

Chandra data

At least 80% of X-ray background is made of discrete sources including two new types:

Very distant galaxies with faint black holes Bright black holes without visible galaxies

Results were from comparing Chandra data to deep optical surveys from Keck


36

CGRO/EGRET data

30-40% of gamma-ray background is unresolved and extragalactic in origin


37

What are the next questions?

What is the distribution of sizes of the fluctuations in the Cosmic Microwave Background?

What do the fluctuations tell us about the dark matter? About the Hubble constant?

Have we really seen enough objects to make up the entire X-ray background?

Is the extra-galactic gamma-ray background similar to the X-ray background?


38

Microwave Anistropy Probe

Selected by NASA in 1996

Will be launched in Fall 2000 to L2

Will measure fluctuations in CMBR on a scale of 0.2 - 1 degrees (vs. 7o for COBE) and fill in the fluctuation plot

How old is the Universe?

How fast is it expanding?

Is the Universe infinite?

Is there really a cosmological constant?

When did the first stars form?

What is the origin of structure in the Universe?


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L2 is one of the 3 unstable points in the Earth-Sun binary systemAnother body can orbit at this point at a fixed distance from the Earth and the Sun with corrections every 23 days


40



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Dipole as predicted byi MAP simulations

Fluctuations as predicted by MAP

simulations


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MAP limits

MAP will have error bars as shown in yellow, improving data until about Leff = l000


43

Planck

ESA mission to be launched in 2007

Will measure entire sky to 10’ to 2 parts per million

Will give better information than MAP for Leff from 600 to 2000


44

Planck

COBE vs. Planck

What Planck will see


45

Gamma-ray Background

Simulated sky as seen by GLAST after 1 year of observation

Key goal to determine if extra-galactic gamma-radiation is from discrete sources


46

Web Resources

Cosmic Background Explorer http://space.gsfc.nasa.gov/astro/cobe/cobe_home.html

Microwave Anistropy Probe http://map.gsfc.nasa.gov

Planck mission http://astro.estec.esa.nl/SA-general/Projects/Planck/

BOOMERanG http://www.physics.ucsb.edu/~boomerang/


47

Web Resources Ned Wright’s CMBR pages

http://www.astro.ucla.edu/~wright/CMB-DT.html

Bell Labs Cosmology Archives http://www.bell-labs.com/project/feature/archives/cosmology/

GLAST project outreach web site http://www-glast.sonoma.edu

MAXIMA experiment http://cfpa.berkeley.edu/group/cmb/

Chandra X-ray Background Results http://chandra.harvard.edu/press/00_releases/press_011400bg.html


48

Question of the Week

Is there background radiation at all wavelengths?

A) No, only at microwave wavelengths

B) No, only at microwave, X-ray and gamma-ray wavelengths

C) Yes and it is the same intensity at all wavelengths

D) Yes but the radiation is different intensities at different wavelengths

april 17, 2001lynn cominsky - cosmology a3501 answer to last week’s question how do we know that...

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