3K background radiation
by
Roman Werpachowski
and
Peter Holrick
Structure
Overview and Background
l Aim and how to reach it
l COBE
l
– Technical Information
– Interpretation of maps
– Maps
l
Other projects in the future
What we will look at?
Source: Rod Nave, HyperPhysics, http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
What we will look at?
Source: Rod Nave, HyperPhysics, http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
What is detected?
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Microwave Background Radiation (MBR):
wavelength=mm to cm
l In terms of photons, or packets of light,
there are quite a few of them in the
microwave background -- about 400 per
cubic centimeter.
l Travelling at the speed of light
l Our eyes can‘t see it
l TV waves are similar to 3k radiation => on
terrestic TVs few percent of the snow is
CMB (Cosmic microwave background)
Source: Wayne Hu, An Introduction to the Cosmic Microwave Background, http://background.uchicago.edu/~whu/beginners/introduction.html
What do we see?
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By looking in the sky, we
actually look backwards in time
Light from more distant objects
takes longer to reach us
We can see back a few billion
years
MBR is from an 300 000 year
old universe:
Soup of fundamental particles
like electrons, protons, helium
nuclei, neutrinos
Source: Wayne Hu, An Introduction to the Cosmic Microwave Background, http://background.uchicago.edu/~whu/beginners/introduction.html
Why 2,73° K?
Because of the expansion, the microwave
background is very cold now - 3 degrees
above absolute zero.
l It's wavelength has
been stretched out
of the visible and
into the microwave
regime of millimeters
to centimeters.
l Temperature is
almost constant.
l
Source: Wayne Hu, An Introduction to the Cosmic Microwave Background, http://background.uchicago.edu/~whu/beginners/introduction.html
Rod Nave, HyperPhysics, http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
Temperature anisotropies
Small variations in the temperature of the
background radiation from point to point on
the sky are called anisotropies.
l These anisotropies were first detected for the
whole sky by the COBE satellite in 1989.
l They produced a
map of the sky:
l
colors represent temperature on the sky
Source: Wayne Hu, An Introduction to the Cosmic Microwave Background, http://background.uchicago.edu/~whu/beginners/introduction.html
Structure
Overview and Background
l Aim and how to reach it
l COBE
l
– Technical Information
– Interpretation of maps
– Maps
l
Other projects in the future
Aim:
l
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To understand how the universe went
from a smooth particle soup to a complex
system of galaxies
Using the surface
Simulation under:
of the soup in the
http://background.uchicago.edu/
microwave back~whu/beginners/instability.html
ground to help
understand and
solve this question
Source: Wayne Hu, An Introduction to the Cosmic Microwave Background, http://background.uchicago.edu/~whu/beginners/instability.html
The data analysis pipline
Sky
MultiFrequency
maps
Measurement
Foreground
removal
Raw data
Sky map
Cleaning
Power
estimation
Timeordered
data
Mapmaking
Power spectrum
Model
Testing
Source: Max Tegmark, CMB data analysis center, http://www.hep.upenn.edu/~max/cmb/pipeline.html
Parameter
estimates
Why power spectrum estimation?
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If the statistical properties of the CMB fluctuations are
isotropic and Gaussian (which they are in the standard
inflationary models), then all the cosmological
information in a sky map is contained in its power
spectrum
This means that all the information from even a giant data
set (say a map with n=10^7 pixels) can be reduced to just
a couple of thousand numbers, greatly facilitating
parameter estimation
It allows a model-independent comparison between
different experiments
one-to-one correspondence between visible features in
the power spectrum and the physical processes one is
studying
Source: Max Tegmark, CMB data analysis center, http://www.hep.upenn.edu/~max/cmb/pipeline.html
Angular power spectrum of
CMB anisotropies
Experiments:
•
Satellites
•
•
•
•
Balloon-born
•
•
COBE
MAP
Planck (COBRAS/SAMBA)
FIRS, ARGO, MAX, M S A M,
B A M, QMAP (Princeton, Penn,
QMASK data), BOOMERanG,
MAXIMA, Top Hat, H A C M E,
A C E, Archeops, BEAST
Ground-based
•
Tenerife,
South Pole,
Saskatoon,
Python,
and many more (>20)
multipole space
S o u r c e: M a x T e g m a r k , C M B d a t a a n a l y s i s c e n t e r, h t t p : / / w w w. h e p. u p e n n. e d u / ~ m a x/ c m b/ e x p e r i m e n t s . h t m l
Structure
l
l
l
Overview and Background
Aim and how to reach it
COBE
– Technical Information
– Interpretation of maps
– Maps
l
Other projects in the future
COBE - Cosmic Background Explorer
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The COBE satellite was developed by NASA's Goddard
Space Flight Center to measure the diffuse infrared and
microwave radiation from the early universe to the limits
set by our astrophysical environment.
launched November 18, 1989
3 instruments:
– Far Infrared Absolute Spectrophotometer (FIRAS) to compare
the spectrum of the cosmic microwave background radiation
with a precise blackbody,
– Differential Microwave Radiometer (DMR) to map the cosmic
radiation sensitively, and
– Diffuse Infrared Background Experiment (DIRBE) to search for
the cosmic infrared background radiation.
The COBE datasets were developed by the NASA Goddard Space Flight Center under the guidance of the COBE Science Working Group and
were provided by the NSSDC.
Source: The COBE Home Page, http://space.gsfc.nasa.gov/astro/cobe/
COBE - Cosmic Background Explorer
FIRAS: Principle
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Should measure precisely the spectrum of the cosmic microwave background
radiation over the wavelength range from 0.1 to 10 mm
7 degree field of view
polarizing Michelson interferometer with bolometer detectors to determine the
intensity of the incoming light at a large number of wavelengths (i.e., a
spectrum) simultaneously.
Far Infrared Absolute Spectrophotometer (FIRAS)
Cosmological discovery:
FIRAS
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The cosmic microwave background (CMB) spectrum is
that of a nearly perfect blackbody with a temperature of
2.725 +/- 0.002 K.
This observation matches the predictions of the hot Big
Bang theory extraordinarily well
It indicates that nearly all of the radiant energy of the
Universe was released within the first year after the Big
Bang.
Far Infrared Absolute Spectrophotometer (FIRAS)
DMR
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Differential Microwave Radiometer (DMR)
Should detect anisotropy
2 antenna for each wavelengt: 3.3, 5.7 and 9.6mm
Antennas are 60 degrees apart
Antenna are switched to ensure difference comes
from the sky and not from differences in the
antennas
7 degree field of view
Cosmological discovery: DMR
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The CMB was found to have intrinsic "anisotropy" for
the first time, at a level of a part in 100,000.
These tiny variations in the intensity of the CMB over the
sky show how matter and energy was distributed when
the Universe was still very young.
Later, through a process still poorly understood, the early
structures seen by DMR developed into galaxies, galaxy
clusters, and the large scale structure that we see in the
Universe today.
Differential Microwave Radiometer (DMR)
DIRBE
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Should minimize response to objects
outside the desire 0.7 degrees view
Internal temperature comparison
Ten wavelengths (1.25 to 240 ì m )
Polarisation at three shortest
wavelengths
Diffuse Infrared Background Experiment (DIRBE)
Cosmological discovery:
DIRBE
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Infrared absolute sky brightness maps in the wavelength
range 1.25 to 240 microns were obtained to carry out a
search for the cosmic infrared background (CIB).
The CIB was originally detected in the two longest
DIRBE wavelength bands, 140 and 240 microns, and in
the short-wavelength end of the FIRAS spectrum.
Subsequent analyses have yielded detections of the CIB
in the near-infrared DIRBE sky maps.
The CIB represents a "core sample" of the Universe; it
contains the cumulative emissions of stars and galaxies
dating back to the epoch when these objects first began to
form.
Diffuse Infrared Background Experiment (DIRBE)
Interpretation of COBE-maps
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Theoretical map, if COBE looked down
2 dimensional representation of the 3
dimensional surface of the earth
Source: Wayne Hu, An Introduction to the Cosmic Microwave Background, http://background.uchicago.edu/~whu/beginners/introduction.html
Interpretation of COBE-maps
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COBE has rather blurry vision and can
only see large features corresponding to 7
degree separations on the sky
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Result:
Source: Wayne Hu, An Introduction to the Cosmic Microwave Background, http://background.uchicago.edu/~whu/beginners/introduction.html
Interpretation of COBE-maps
l
COBE also has noise in its detectors like
you would have with bad reception on
your TV
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Result:
Source: Wayne Hu, An Introduction to the Cosmic Microwave Background, http://background.uchicago.edu/~whu/beginners/introduction.html
Interpretation of COBE-maps
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To get rid of the noise, maps can be
smoothed. This brings out the large
features like continents but fine details are
lost in the map
Result:
Source: Wayne Hu, An Introduction to the Cosmic Microwave Background, http://background.uchicago.edu/~whu/beginners/introduction.html
Interpretation of COBE-maps
l
Similarly COBE's map of the background
radiation only shows you the large
features in the sky and all finer details are
lost.
Source: Wayne Hu, An Introduction to the Cosmic Microwave Background, http://background.uchicago.edu/~whu/beginners/introduction.html
Example maps
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Maps based on observations
made with the DMR over the
entire 4-year mission, at each
of the three measured
frequencies, following dipole
subtraction.
the red and blue spots
correspond to regions of
greater or lesser density in
the early universe.
Differential Microwave Radiometer (DMR)
Example maps
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Maps based on 53 GHz (5.7
mm wavelength) observations
made with the DMR over the
entire 4 year mission (top) on a
scale from 0 - 4 K,
showing the near-uniformity of
the CMB brightness, (middle)
on a scale intended to enhance
the contrast, and
(bottom) following subtraction
of the dipole component.
Emission from the Milky Way
Galaxy is evident in the bottom
image.
Example maps
structured, warmer
emission from
interplanetary dust
Orion molecular clouds, which
are active "stellar nurseries" in
our Galaxy
Large and Small
Magellanic Clouds
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This image combines data from the DIRBE obtained at infrared wavelengths of 25, 60 and 100 µm.
The sky brightness at these wavelengths is represented respectively by blue, green, and red colors in the
image.
The image is dominated by the thermal emission from interstellar dust in the Milky Way.
Example maps
structured, warmer
emission from
interplanetary dust
Orion molecular clouds, which
are active "stellar nurseries" in
our Galaxy
Large and Small
Magellanic Clouds
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This image combines data from the DIRBE obtained at infrared wavelengths of 100, 140 and 240 µm.
The sky brightness at these wavelengths is represented respectively by blue, green, and red colors in the
image.
The image is dominated by the thermal emission from interstellar dust in the Milky Way.
Structure
l
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l
Overview and Background
Aim and how to reach it
COBE
– Technical Information
– Interpretation of maps
– Maps
l
Other projects in the future
Microwave Anisotropy Probe
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The Microwave Anisotropy Probe (MAP) will make a
map of the temperature fluctuations of the CMB radiation
with much higher resolution, sensitivity, and accuracy
than COBE.
MAP is the first mission to use an L2 orbit as its
permanent observing station. L2 is a semi-stable region
of gravity that is about 4 times further than the Moon,
following the Earth around the Sun.
June 30, 2001: MAP Launch
Oct. 1, 2001: MAP Arrives at L2
One full sky scan last 6 months
Jan. 2003: First Data Release
S o u r c e: h t t p : / / m a p. g s f c. n a s a. g o v/ m _ m m / m s _s t a t u s . h t m l
Microwave Anisotropy Probe
Source: http://map.gsfc.nasa.gov/m_mm/ms_status.html
PLANCK
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To be launched in the
first quarter of 2007
By European Space
Agency
Better and more
instruments
L2 orbit
Source: http://astro.estec.esa.nl/SA-general/Projects/Planck/
Aim:
To understand how the universe went
from a smooth particle soup to a complex
system of galaxies
l Using the surface
Simulation under:
of the soup in the
http://background.uchicago.edu/
microwave back~whu/beginners/instability.html
ground to help
understand and
solve this question
l
Source: Wayne Hu, An Introduction to the Cosmic Microwave Background, http://background.uchicago.edu/~whu/beginners/instability.html
Degree Angular Scale
Interferometer (DASI)
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Polarization of CMB also supports current models
of the universe