Download The Cosmic Microwave Background

The Cosmic Microwave
Background
Università degli studi di
Napoli Federico II
Viviana Gammaldi
Matr. 242/011
Contents
•The Big Bang Theory
•The Cosmic Microwave Background
• The experiments (COBE, WMAP, PLANK)
The Big Bang theory
The Big Bang theory postulates that ~ 14 billion years ago, the
portion of the universe we can see today was only a few
millimeters across: we can see remnants of this hot dense
matter as the now very cold cmb radiation which still pervades
the universe as a uniform glow across the entire sky. The Big
Bang theory rests on:
•General Relativity: gravity is supposed to be a distortion of
space and time itself .
• The Cosmological Priciple: the universe is homogeneous
and isotropic when averaged over very large scales.
The Big Bang theory
Given the GR and the CP, the distortion
of space-time, due to the gravitational
effects of this matter can only be
positively or negatively cuved or flat.
About the dynamics of the universe, it started
from a very small volume with an initial
expansion rate: a key question is whether or not
the pull of gravity is strong enough
to ultimately reverse the expansion and cause
the universe to collapse back on itself (Big
Crunch).
The Big Bang theory
There are free parameters of Big
Bang model that must be fixed by
observations of our universe:
• the geometry of the universe ΩK
(open, flat or closed);
•the Hubble constant H0;
•the overall course of expansion q,
past and future, which is determined
by the fractional density of the
different types of matter in the
universe :
•Radiation Ωr
•Baryonic matter Ω B,
•Dark Matter Ω DM
•Dark energy ΩΛ
Tests of the Big Bang theory
The Big Bang Model is supported by important observations:
Expansion:
1917 Einstein invetend a Cosmological costant Λ
1929 The Hubble’s expansion law is v = Hd.
2001 WMAP satellites results show:
H = 71.9 −+22..67 kms −1Mpc −1
Light elements: The Big Bang nucleosynthesis: it is
in good agreement with observations. Elements
heavier than lithium are all synthesized in stars.
Elements heavier than iron are produced both in
super-giant stars and in the explosion of a
supernovae
Tests of he Big Bang theory
•CMB: observed in 1965 by Penzias and Wilson. The CMB radiation is
very cold, only 2.725 K, thus this radiation shines primarily in the
microwave portion of the electromagnetic spectrum. The uniformity is the
reason to interpret the radiation as remnant heat from the Big Bang. The
CMB photons easily scatter off of electrons: this produces a blackbody
spectrum of photons, according to the Big Bang theory.
The Big Bang theory
The behavior of CMB photons moving through the early universe is
analogous to the propagation of optical light through the Earth’s
atmosphere: we can look through the air out towards the clouds, but can
not see through the opaque clouds. Cosmologists studying
the CMB radiation can look through
much of the universe back to when it
was opaque: a view back to 400,000
years after the Big Bang. This wall
of light is called the surface of last
scattering .
Beyond Big Bang cosmology
The Big Bang model is not complete:
• The flatness problem: a universe as flat as we see it today would
require an extreme fine-tuning of conditions in the past;
• The horizon problem: distant regions of space in opposite directions,
assuming standard Big Bang expansion, they could never have been in
causal contact with each other: the uniformity of the CMB temperature
tells us that these regiions are in thermal equilibrium;
• The monopole problem: Big Bang cosmology predicts that stable
”magnetic monopoles” should have been produced in the early universe.
However, magnetic monopoles have never been observed;
• The origin of the structure problem: the universe is omogeneous and
hisotropic only on large scales, while on small scales there are a lot of
anysotropies, such as stars an galaxies.
Beyond Big Bang cosmology
The Inflation Theory proposes a period of exponential expansion of the universe prior
to the more gradual Big Bang expansion and offers solutions to these problems :
• The flatness problem: the surface of the Earth appear flat to you, even
though it is still a sphere on larger scales. Inflation stretches any initial
curvature of the 3-dimensional universe to near flatness;
• The horizon problem: distant regions were actually much closer
together prior to Inflation than they would have been with only standard
Big Bang expansion.
• The monopole problem: Inflation allows for magnetic monopoles to
exist as long as they were produced prior to the period of inflation.
During inflation, the density of monopoles drops exponentially;
• The origin of the structure problem: prior to inflation quantum
fluctuation in the density of matter on microscopic scales expanded to
astronomical scales during Inflation: the higher density regions
condensed into stars, galaxies, and clusters of galaxies
Beyond Big Bang cosmology
While gravity can enhance the tiny fluctuations seen in the early
universe, it can not produce these fluctuations. Different theories to
produce the primordial fluctuations make very different predictions about
the properties of the CMB fluctuations. The inflationary theory predicts
that the largest temperature fluctuations should have
an angular scale of one degree,
while the defect models predict
a smaller characteristic scale.
WMAP indicates that the
inflationary model is more
likely.
However, the Big Bang
theory successfully explains
the ”blackbody spectrum” of
the CMB radiation.
Beyond Big Bang cosmology
•When cosmologists first looked at
the microwave sky, they noticed it
was nearly uniform.
•As observations improved, they
detected the dipole anisotropy.
•1992, COBE satellite made the
first detection of fluctuation : one
part of the sky has a temperature of
2.7251 K , while another part has a
temperature of 2.7249 K.
Two main sources for the
fluctuations:
• Emission from the Milky Way;
• Fluctuating emission from the
edge of the visible universe;
• There is also residual noise
Temperature of the microwave sky in a
scale in which Blue is 0K and Red is 4K:
Green is because T=2.725K
Blue -> 2.721K Red ->
2.729K
The ”yin-yang” pattern
is the dipole anisotropy
that results from the
motion of the Sun
relative to the rest frame
of the CMB.
CMB after the
dipole
anisotropy has
been subtracted.
Red is 0.0002K
hotter than the
cold regions
(Blue)
The CMB anisotropies
Before z*≈103 the tightly coupled system
of photons, electrons and protons
behaved as a single gas: photons pression
resists gravitational compression of the
fluid sets up acoustic oscillations.
Further, the compressions heated the gas
and the rarefactions cooled it.
At z*,of recombination, about 380,000
years after the Big Bang, the photons
were no longer scattered, so they traveled
through space. Photons released from hotter, denser areas were more
energetic than photons emitted from rarefied regions, so the pattern of hot
and cold spots induced by the sound waves was frozen into the CMB: we
call these fluctuations primary anisotropies, while a secondary
anisotropies can also be generated between recombination and the present.
The CMB anisotropies
At z*,, denser areas of matter coalesced into stars and galaxies under the
attractive influence of gravity.
Inside the horizon, acoustic, Doppler, gravitational redshift and photon
diffusion effects combine to form a seemingly complicated spectrum of
primary anisotropies: Considering the component contributions
individually reveals the spectrum and the cosmological parameters.
Secondary effects
may provide important clues for
the process of structure formation.
From inflaction to recombination
The inflation provides a physical mechanism for triggering the
primordial sound waves and all the structure in the universe, through
inflaton: quantum fluctuations in the provide initial disturbances that are
approximately equal on all scales, that become fluctuations in the energy
density in the primordial plasma. Because inflation produced the density
disturbances all at once moment, the phases of all the sound waves were
synchronized.
Consider blowing into a pipe that is open at both ends: the fundamental
frequency of the sound corresponds to a wavelenght with maximum air
compression at the mouthpiece end minimum compression (maximum
rarefaction) at the end piece.
But the sound also has a series of
overtones corresponding to
wavelengths that are integer
fractions of the fundamental
wavelength..
From inflaction to recombination
The sound waves in the early universe oscillating in time instead of
space.
Assume that a certain region of space
has a maximum positive displacement,
that is maximum temperature, at
inflation. As the sound waves
propagate, the density of the region
will begin to oscillate. The wave that
causes the region to reach maximum
negative displacement exactly at
recombination is the fundamental wave of the early universe. The
overtones have wavelengths that are integer fractions of
the fundamental wavelength: they cause smaller regions of space to reach
maximum displacement, either positive or negative, at recombination.
The angular power spectrum
Plotting the magnitude of the temperature
variations against the sizes of the hot and cold
spot providing a map of temperature variations
across the whole sky (a).
Taking an angular decomposition of the
fluctuations in multipole space l, proportional
to the inverse angle (l=100≈θ=1° ), we get the
angular power spectrum of CMB anisotropies
∞
l
.
m m
f (θ , φ ) = ∑ ∑ Cl Yl (θ , φ )
l =0 m = −l
The series of peaks supports the inflation, but the
sound waves should have nearly the same
amplitude on all scales. The power spectrum
shows a drop-off in the magnitude of temperature
variations after the third peak, because a wave
cannot propagate if its wavelength is shorter than
the mean free path of the particles.
The angular power spectrum
The position of that first peak in the power
spectrum of the anisotropies depend
sensitively on the spatial curvature of the
universe. As the curvature decreases the peaks
move to higher multipole l while preserving
their shape; dark energy makes the universe
flat despite a sub-critical density of matter.
The CMB reveals the angular size of the most
Intense temperature variations and knowing the
distance CMB photons have traveled before reaching
Earth with the classic test of spatial curvature it’s possible estimate the
geometry of the universe: the universe obeys the laws of Euclidean
geometry and must be very close to spatially flat, and so the average
matter density is close to the critical density ρ0=10-29gcm−3.
The angular power spectrum
The next thing we would like to know is the exact breakdown of the universes matter and
energy. Gravity can enhance or counteract sonic compression and rarefaction. Both
ordinary matter and dark matter supply mass to the primordial gas.
At recombination the fundamental wave
is frozen in a phase where gravity and
sonic motion have worked together to raise
The radiation temperature in the troughs
(blue) and lower the temperature at the
peaks (red) (up).
At smaller scales, the first overtone is
caught in the opposite phase, gas
pressure is trying to expand the
plasma (blue arrows), while gravity
tries to compress it (white arrows).
This tug-of-war decreases the
temperature differences, which explains
why the second peak in the power spectrum is lower than the first.
The angular power spectrum
Comparing the heights of the two peaks,
cosmologists can gauge the relative strengths of
gravity and radiation pressure. The Baryon
density Ωbh2 make the first acoustic peak much
larger than the second. The more baryons the
more the second peak is relatively suppressed.
Baryons constitute about 5% of the critical
density today, in agreement with the number
derived from studies of light element synthesis in
the infant universe.
An abundance of cold dark matter was needed
to keep the gravitational-potential wells
sufficiently deep. By measuring the ratios of
the heights of the first three peaks, researchers
have determined that the density of cold dark
matter ΩDMh2 constitutes ~21% of the critical
density. Notice also that the location of the first
peak in particular changes as we change the
DM density.
The angular power spectrum
These calculations of matter and energy leave ~74% of the critical
density unspecified, so theorists have
posited the dark energy: most of the
universe today is composed of
invisible dark matter and dark energy,
both seem to be coincidentally
comparable in energy density today.
Another mysterious component,
the inflaton, dominated the very early
universe and seeded cosmic structure.
The energy densities of DM and DE, as
measured from the CMB, are in striking
accord with these astronomical
observations.
The angular power spectrum
The existence of DE also predicts additional
phenomenain the CMB,like the so-called the
integrated Sachs-Wolfe effect, causes
large-scale temperature variations
in the CMB. The amount of DE needed to produce
the large-scale temperature variations is consistent
with the amount inferred from the acoustic peaks
and the distant supernovae: the ISW effect could
become an important source of information about
dark energy.
In 1968 Silk predicted (by MCS) that radiation
should gain a small but known polarization: on the
small scales photons can travel with relatively few
scatterings, so they retain directional information that
is imprinted as a polarization of the CMB. The value
misured by WMAP was in agreement with
predictions: WMAP also detected polarization on
larger scales that was caused by scattering of CMB
photons after recombination.
The next investigations
Measurements of the CMB have dramatically strengthened the case for the
simplest models of inflation.
Another exciting possibility is that we could learn about the physics of
inflation by determining the energy scale at which it took place: inflation
created fluctuations in the space-time itself, that is gravitational waves,
whose amplitude is proportional to the square of the energy scale at which
inflation took place.
Measurements of the Sunyaev-Zeldovich effect allows
galaxy clusters to be identified during the crucial period,
about five billion years ago, when dark energy began to
accelerate the expansion of the universe.
The second phenomenon, gravitational lensing,
happens when CMB photons pass by a
particularly massive structure that distorts the
pattern of temperature and polarization variations.
The degree of lensing reveals the amplitude of the
mass density fluctuations associated with these
structures.
The next investigations
To conduct these investigations of inflation and dark energy, however,
researchers will need a new generation of CMB telescopes.
In may 14th 2009 the European Space Agency (ESA) launched the
PLANCK spacecraft.
The higher resolution and lower noise of the Planck satellite allows it to
measure further out into the series of acoustic peaks and so gather more
information from them. Notice however
that both experiments have the same
errors at low multipoles.
So I’ll analyze now the main experiments
about the CMB, and the huge improvement
that the researcher made in this field.
COBE:Cosmic Background Explorer
The COBE satellite was developed by NASA’s Goddard Space Flight Center launched
November 18, 1989 to measure the diffuse infrared and microwave radiation from the
early universe.
A gold-colored sun shield
Cylindrical metal tank.
Painted on
the side
of the
rocket are
the
triangular
”Delta”
logo and the
COBE logo
3 wings of solar
panels: they fitted
up next to the
satellite sides
when the wings
were folded for
launch.
The bottom section
COBE:Cosmic Background Explorer
COBE carried three instruments:
• DIRBE: Diffuse Infrared
Background Experiment to search
for the cosmic infrared
background radiation (CIB) in the
range from 1 to 1000 µm. The
primary aim is to conduct a search
for an isotropic CIB radiation and
to measure its energy distribution.
Secondary objectives include
studies of foreground
astrophysical sources. The
observational approach is to make
absolute brightness maps of the
full sky at ten wavelengths from
1.2 to 240 µm and to map linear
polarization at 1.2, 2.2, and 3.5
µm.
The emission from stars and dust in the
Galactic plane (horizontal feature) and
light scattered and emitted by dust in the
solar system (S-shape). The zodiacal
(emission from the solar system dust,
strongest at 25 µm , but
also in evidence in the 100 µm image and
to a lesser degree at the longer
wavelengths) and Galactic emission must
be precisely modeled and subtracted in
order to detect the relatively faint CIB.
COBE:Cosmic Background Explorer
• DMR: Differential Microwave Radiometer maps the cosmic
radiation sensitively. The CMB was found to have intrinsic
”anisotropy” for the first time, at a level of a part in 100,000.
Each antenna has a 7 degree (FWHM) beam, giving an
effective angular resolution of 10 degrees. 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.
• FIRAS: Far Infrared Absolute Spectrophotometer compares the spectrum of the CMB
radiation with a precise blackbody. It is a polarizing Michelson interferometer operated
differentially with an internal reference blackbody,
and calibrated by an external blackbody having an
estimated emissivity of better than 0.9999. It covers
the wavelength range from 0.1 to 10 mm in two
spectral channels separated at 0.5 mm and has
approximately 5% spectral resolution. FIRAS
measured a nearly perfect blackbody spectrum of
the CMB with a temperature of 2.725 +/- 0.002 K.
COBE:Cosmic Background Explorer
The COBE cryogenics, propulsion and Fluid Systems Branch Components are:
• Spacecraft propulsion module
• Infrared bolometers: The FIRAS and DIRBE instruments on COBE
require these long wavelength infrared detectors: COBE has bolometers
with sensitivity more than an order of magnitude better than required.
A bolometer is a device for measuring the
energy of incident electromagnetic radiation. It
consists of an ”absorber” connected to a heat
sink (area of onstant temperature) through an
insulating link. The result is that any radiation
absorbed by the absorber raises its temperature
above that of the heat sink: the higher the
energy absorbed, the higher the temperature
will be. Temperature change can be measured
directly or via an attached thermometer.
COBE:Cosmic Background Explorer
• Flight helium dewar: The COBE dewar was a 660 liter liquid helium cryostat. It
provided a stable 1.4 Kelvin environment for the two cold instruments, FIRAS and
DIRBE. The first phase of the COBE science mission came to an end on Friday,
September 21, 1990, after 306 days
of cryogenic operations as the last
of the superfluid helium contained
within the dewar was consumed.
•Test dewars: The COBE test dewar
is a cylinder 10 to 12 feet high, a few
feet in diameter. The label
”COBE ITD” identifies the test dewar.
• Dewar Vent Line Analysis: The sensitivity of the FIRAS and DIRBE detectors is highly
dependent on their operating temperature. The vent analysis correlated well with on-orbit
conditions, confirming other dewar temperature data and lifetime predictions. The
analysis was performed by Code 713 (now Code 552).
WMAP :Wilkinson Microwave Anisotropy Probe
The WMAP satellite was launched on 30 June 2001, from Florida.
A (94 cm
diameter x 33
cm length x
0.318 cm thick)
gamma-alumina
cylindrical shell
provides low
thermal
conductance
between the
warm spacecraft
and the cold
instrument
components.
Deployed sun shield (5 m in diameter) keeps
the spacecraft and instrument in shadow for
all nominal science operations.
The Observatory is 3.8 m
tall and its mass is 836 kg.
Large passive radiators are connected
directly to amplifiers at the core of the
radiometers.
WMAP :Wilkinson Microwave Anisotropy Probe
The WMAP mission is designed to determine the geometry, content, and
evolution of the universe via a 13 arcminute FWHM resolution full sky
map (>95%) of the temperature anisotropy of the CMB radiation: the
WMAP mission characteristics are:
• ≈ 2° angular resolution
• Accuracy on all angular scales > 0.2°
• Minimally correlated pixel noise
• Polarization sensitivity
• Accurate calibration (< 0.5% uncertainty)
• An overall sensitivity level of ∆Trms< 20µK
per pixel
• Systematic errors limited to < 0.5% of the
random variance on all angular scales
WMAP :Wilkinson Microwave Anisotropy Probe
The choice of orbit, sky-scanning strategy and instrument/spacecraft design were driven
by the goals of uncorrelated pixel noise, minimal systematic errors, multifrequency
observations, and accurate calibration.
To minimize systematic errors WMAP has:
• Symmetric differential design: two sky signals, from directions separated by ~141°,
are reflected via two nearly identical back-to-back primary reflectors towards two
nearly identical secondary reflectors and into 20 feed horns, 10 in each optical path. The
off-axis Gregorian design allows for a sufficient focal plane area, a compact
configuration that fits in the Delta-rocket fairing envelope. The principal focus of each
optical path is between its primary and its secondary mirror.
The Gregorian telescope is a reflecting
telescope: the primary mirror collects the light
and brings it to a focus before the secondary
mirror where it is reflected back through a hole
in the centre of the primary.
WMAP :Wilkinson Microwave Anisotropy Probe
• Rapid large-sky-area scans: the ideal scan strategy would be to
instantaneously scan the entire sky. Practical constraints limit the scan
rate. For a space mission, increasing the scan speed rapidly becomes
expensive. It is possible to assess the quality of a sky scanning strategy
by computer simulations.
• L2 orbit to minimize contamination from Sun, Earth, and Moon
emission and allow for thermal stability: to minimize thermal and
electrical variations the solar arrays maintain a
constant angle relative to the Sun of 22.5°± 0.25°
during CMB anisotropy observations at L2.
•Multiple independent channels: MAPs
Microwave System consists of ten 4-channel
differencing assemblies, each of which receives
two orthogonally polarized signals from a pair of feeds. The signals are
combined in a way such as there are 20 statistically independent signal.
WMAP :Wilkinson Microwave Anisotropy Probe
•5 frequency bands to enable a separation of galactic and cosmic signals:
Four physical mechanisms that contribute to the galactic emission are
synchrotron radiation, free-free radiation, thermal
radiation from dust. There are three approaches that
can be used. I) to scale and subtract to the MAP
existing galactic maps. II) to form linear combinations
of the multi-frequency MAP. III) to determine the
Spatial and/or spectral properties of each one.
All three of these techniques were employed with
some degree of success with the COBE data.
Those techniques also generally reduce extragalactic
contamination.
The most affected MAP pixels should be masked and
not used. Hot gas in clusters of galaxies will also contaminate the maps
by shifting the spectrum of the primary anisotropy to create a SunyaevZeldovich decrement in the MAP frequency
WMAP :Wilkinson Microwave Anisotropy Probe
• Passive thermal control with a constant Sun angle for thermal and
power stability: there are three major objectives of the thermal sign of
MAP. I) to keep all elements of the Observatory within nondestructive
temperature ranges. II) to passively cool the instrument front-end
microwave amplifiers and reduce the microwave emissivity of the frontend components to improve sensitivity. III) to minimize all thermal
variations during the nominal observing mode.
• Precision temperature sensing at selected instrument locations: there are
precision platinum resistance thermometers (PRTs) at various locations
to provide a quantitative demonstration of thermal stability at the submillikelvin level. The information from these sensors is invaluable for
making a quantitative assessment of the errors and could be used to make
error corrections in the ground data reduction pipeline. The design is to
make these corrections unnecessary and to use the sensor data only to
prove that thermal variations are not significant.
WMAP :Wilkinson Microwave Anisotropy Probe
• Main beam pattern measured accurately in-flight: Jupiter serves as the source for
beam pattern measurements in-flight. Beam patterns were measured in an indoor
compact antenna range at the Goddard Space Flight Center and the far-sidelobes were
measured between rooftops at Princeton University.
• Control of beam sidelobe levels to keep the Sun, Earth,
and Moon levels <1µK: Those emission can contaminate the
Raw data by entering the instrument via the sidelobes of the
beams. A source of external emission is the dipole signal
induced by MAP’s motion with respect to the Sun: this effect
is treated as a calibration error.
• Calibration determined in-flight: the instrument is calibrated in-flight using
observations of the CMB dipole and of Jupiter. Despite the in-flight amplitude
calibration, it was necessary to provide provisional calibration on the ground to
characterize various aspects of the instrument to assure that all requirements would be
met.
Observations of Jupiter and other celestial sources provide an in-flight pointing offset
check relative to the star tracker pointing. The pointing directions of the feeds were
measured on the ground using standard optical alignment techniques.
WMAP :Wilkinson Microwave Anisotropy Probe
In the first release of WMAP data (February 2003), only the temperature data and
analyses from the first year of operations at L2 were provided:
•Data from the first three years of spacecraft operations at L2 are made available.
•Polarization analysis, maps, and time-ordered data are made available.
•The temperature analysis and maps are improved.
•The error analysis was improved.
•The map-making algorithm was changed.
Much more information and data was provided in the second release (March 2006):
•Data from the first five years of spacecraft operations at L2 are made available.
•The temperature and polarization analysis and maps are improved.
•The error analysis was improved.
•The calibration algorithm was improved.
•The beam maps were improved.
WMAP :Wilkinson Microwave Anisotropy Probe
The following CMB anisotropy observables should be seen within the context of the
simplest form of inflation theory (a single scalar field with adiabatic fluctuations):
• an approximately scale-invariant spectral index of primordial fluctuations n≈1;
• a flat Ω0 = 1 geometry, which places the first acoustic peak in the CMB fluctuation
spectrum at a spherical harmonic order l=220;
• no vector component (single scalar field, although vector modes could be introduced
with late-time defects);
• Gaussian fluctuations with random phases;
• a series of well-defined peaks in the CMB power spectrum, with the first and third
peaks enhanced relative to the second peak;
• a polarization pattern with a specific orientation with respect to the anisotropy
gradients.
WMAP :Wilkinson Microwave Anisotropy Probe
The main cosmological parameters measured by WMAP are:
If these numbers are fixed to match an observed temperature spectrum, then the
properties of the polarization fluctuations are nearly completed specified, particularly for
l > 30. If the polarization pattern is not as predicted, then the primordial fluctuations can
not be entirely adiabatic.
PLANCK surveyor
PLANCK is the first European mission to study the birth of the Universe, it has been
carried into space on 14 May 2009 in Kourou, French Guiana:
• 4.2 metres
high and has
a maximum diameter of 4.2 metres,
with a launch mass ~ 1.9 tonnes.
• systems for power
generation and conditioning
• data handling and communications,
together with the warm parts of
the scientific instruments
• payload module. that is the telescope,
•the optical bench, with the parts of the instruments that need to be cooled, the
sensitive detector units, and the cooling systems.
PLANCK surveyor
The PLANCK telescope is an off-axis tilted Gregorian design with a primary
mirror measuring 1.9 x 1.5 m and with an aperture of 1.5 m diameter. The
1.1 x 1.0 m secondary mirror focuses the collected light onto the two
scientific instruments:
• LFI (Low Frequency Instrument), an array of radio receivers using
high electron mobility transistor mixers: The LFI is designed to
produce measurements of the microwave sky in the frequency range
27 to 77 GHz ;
• HFI (High Frequency Instrument), an array of microwave detectors
using spider bolometers equipped with neutron transmutation doped
germanium thermistors: The HFI is designed to produce
Measurements of the diffuse sky radiation in the frequency
range 84 GHz to 1 THz;
The measurements made by the two instruments will be combined to
produce a full-sky map of the anisotropies with unprecedented precision.
The off-axis angle of the telescope design allows the system to minimize the
polarization effects introduced by the telescope. The function of the baffle is
to shield the detectors from thermal radiation originating within the optical
enclosure.
PLANCK surveyor
PLANCK has been carried into space by an Ariane 5 ECA together with
Herschel, an IR space telescope. After launch, PLANCK will
reach its operational orbit L2 located 1.5 million kilometres away from the
Earth. The spacecraft will be operated in a Lissajous orbit around the L2
point with an average amplitude of about 400000 km. Orbits about L2
are dynamically unstable. Planck will use its propulsion system to perform
orbit maintenance manoeuvres.
Planck has a nominal operational lifetime of fifteen months from the end of
the Calibration and Performance Verification Phase.
The Mission Operations Centre is located at ESA’s European
Space Operations Centre in Germany. For communication
with the spacecraft two deep space antennas in Australia and
Spain will be used. The PLANCK science planning in Spain.
The data processing and the operations centre for the HFI
Instrument are both located in France, whereas those for the
LFI instrument are located at the Osservatorio Astronomico
di Trieste,Italy.
PLANCK surveyor
The key objectives of PLANCK are as follows:
• Measurement of CMB anisotropies with a temperature resolution (∆T/T)
of the order of 10−6 (astrophysical limit set by small scale fluctuations in
foreground emission) at all angular resolutions greater than 10
arcminutes;
• Test inflationary models, specifically the determination of the spectral
index of the primordial fluctuation spectrum to high precision and the
detection of a component of the CMB anisotropies induced by primordial
gravitational waves;
• Measurement of the amplitudes of structures in the CMB with physical
scales between 100 and 1000 h−1Mpc, that have sizes comparable to the
voids and filaments observed in the galaxy distribution today to establish
a consistent theory of the formation of cosmic structure and shed light on
the nature of the dark matter;
PLANCK surveyor
• Detection of characteristic signatures in the CMB created by topological
defects, such as cosmic strings and textures, generated at a phase
transition in the early Universe;
• Measurements of the Sunyaev-Zeldovich effect: PLANCK will detect
this effect providing information on the physical state of the intracluster
gas and on the evolution of rich clusters, these measurements can also be
combined with spatially resolved X-ray observations to estimate the
Hubble constant H0;
• Using the high sensitivity of PLANCK’s sub-millimetre bolometer
channels, it will be possible to disentangle the frequency dependent
Sunyaev-Zeldovich effect in rich clusters of galaxies from temperature
differences caused by their peculiar motions, providing powerful tests of
theories of structure formation and information on the mean mass density
of the Universe.
Summary
In this seminary I showed an overview of the cosmological standard model of the Big
Bang, with a particullary research on one of its tests: the CMB.
I showed the main features of the CMB and the way to understending them and the
other way round to deducing the cosmological parameters from the experimental data.
Finally I showed the three main experiments on the CMB, their results and
improvement:
The Cosmic Background Explorer (COBE), launched in 1989, determined that the
CMB exhibits anisotropies at a level of 10-5 and angular resolution of 10° and showed
that the CMB spectrum matched that of a black body with a temperature of 2.725K.
The Wilkinson Microwave Anisotropy Probe (WMAP), launched in 2001, made
measurements of the CMB enabling the creation of a map of the anisotropies with 45
times the sensitivity and 33 times the angular resolution on the COBE DMR mission.
PLANCK, launched in 2009, has been designed to have 10 times better sensitivity to
temperature variations of the CMB and more than 50 times the angular resolution of the
COBE spacecraft.