april 17, 2001lynn cominsky - cosmology a3501 answer to last week’s question how do we know that...
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April 17, 2001 Lynn Cominsky - Cosmology A350
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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
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April 17, 2001 Lynn Cominsky - Cosmology A350
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Group 10
Brian Berryessa
Charity Haas
Andrew McFarland
Jessica Rapin
John Wilczak?
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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!
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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
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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
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COBE launch movie
COsmic Background Explorer Launched 11/18/89 into polar orbit
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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
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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
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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
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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
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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”
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COBE data/DMR
Dipole due to movement of Solar System
warm
cool
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COBE data/DMR
Dipole removed to show “wrinkles”
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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
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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
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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
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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
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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)
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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
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X-ray Background
ROSAT 0.75 keV map
Shows smooth blue background plus bright superbubble ring at D=150 pc with R= ~100 pc
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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
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CGRO/EGRET data
30-40% of gamma-ray background is unresolved and extragalactic in origin
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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?
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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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Microwave Anistropy Probe
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
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Microwave Anistropy Probe
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Microwave Anistropy Probe
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
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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
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Planck
COBE vs. Planck
What Planck will see
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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
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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/
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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
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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