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Observable universe and the CMB

Cosmic microwave background radiation

 Automatic translation  Automatic translation Updated June 01, 2013

The electromagnetic radiation from the sky background or Cosmic microwave background radiation (CMB), is a natural radiation of microwaves at low temperatures reaching the surface of the Earth from all directions of the cosmos. It is so called because it forms a background to all radio sources that point were detected by radio telescopes. It was detected for the first time by Arno Penzias and Robert W. Wilson, 1965, Bell Telephone Laboratories in New Jersey. The discovery of the cosmic microwave without specific source is the residue of the extreme conditions that prevailed in the first moments of the Universe. This has led to the conclusion that the universe, there is 13.7 billion years, was at a temperature of at least 3000°C. This background radiation of the sky at 2.7 K, i.e. -270° Celsius. It has not been issued to the birth of the universe but at the time when the universe passes from an opaque state to a transparent state, i.e. light.
Before one can not see the universe, it is opaque, but there are other fossils as the relative abundance of certain elements (Helium, Hydrogen, Lithium heavy). Physicists have come to the conclusion that the universe was at one point at a temperature of at least 10 billion degrees. This period is 1 million years before switching to the transparent state that corresponds to a temperature of 3000 degrees Celsius.


Going back a little in time, the universe reaches temperatures of agenda trillion level. In this state it is not composed of nuclei of neutrons and protons, but a soup of quarks and gluons. Quarks attract and repel by exchanging gluons as the electrons give off photons in the electromagnetic fields. Only when the temperature decreases that quarks combine to form neutrons, protons and mesons. Going back even further, one hundred of a second before, we still find fossils. For example, the number of photons versus the number of atoms is 3 billion.

NB: The parsec is the distance at which one astronomical unit (distance between Earth and the Sun) subtends an angle of one arc second.
Table of equivalences.

pc al au km
pc 1 3,26 206265 3,09x1013
al 0,307 1 63242 9,46x1012
au 4,85x10-6 1,58x10-5 1 1,50x108
km 3,24x10-14 1,06x10-13 6,68x10-9 1
 radiation of the background sky CMB

Image: The radiation of the background sky is a natural radiation of microwaves fossil 2.73 K.
These density fluctuations of the order of 1/100 000th show that about 300,000 years after the Big Bang, there was heterogeneous areas in the universe of a size between 100 and 1000 Mpc (mega parsec).
This image was produced by the COBE satellite in 1992.

Universe in video


What would an imaginary journey throughout the known universe?
To help you visualize this cosmic journey round trip, the American Museum of Natural History has produced a film with virtual images of such a trip.
The video begins with an aerial view of the Himalayas. It zooms spectacular showing in succession, the orbits of artificial satellites of the Earth, Moon, the orbits of planets, constellations, the Sun, the solar system, the sphere occupied by the emission of the first radio signals from the humanity, the Milky Way, nearby galaxies, distant galaxies and quasars up to diffuse cosmic radiation reaching issued by the Big Bang, the glow of the first fossil of the universe transparent light that was emitted at birth of the Universe less than a million years after the Big Bang. We capture this day that light is the cosmic radiation or cosmic microwave background (CMB). The CMB is the "first light" of the universe, published shortly after the Big Bang, there are about 13.7 billion years, when the light began to travel freely for the first time. The huge fireball that followed the Big Bang has cooled slowly to become a background of microwaves. To make this film, the scientists used data from the Digital Universe Atlas. All celestial objects in this video are shown to scale given the data known in 2009 by science.

NB: the Big Bang model favors the existence of a phase of cosmic inflation very brief but during which the universe would have grown extremely rapidly. It is from here that most of the material particles of the universe were created at high temperature, triggering the emission of large amounts of light, called cosmic microwave background. This radiation is now observed with great accuracy by space probes.

Video: Video on a space trip, round trip between Earth and the cosmic horizon of the known Universe. The Known Universe - Credit & Copyright: American Museum of Natural History


Observable universe


The age of the universe has been clarified by observations of the WMAP probe. Cosmological parameters indicate a probable value for the age of the universe about 13.7 billion years with an uncertainty of 0.2 billion years. This is consistent with data from the observation of globular clusters and white dwarfs. The observable universe contains about 7 × 1022 stars, distributed in about 1010 galaxies, which are themselves organized into clusters and superclusters of galaxies. The number of galaxies could be even greater. Why specialize in cosmology often use the term observable universe? Because we see it as it was 13.7 billion years ago but since then the universe has continued to grow. Thus the universe we see is a bubble of 13.7 billion years in radius, which is why we live in the center of the observable universe, in apparent contradiction to the Copernican principle which says that the universe is more or less uniform and has no particular center.


Because light does not move at infinite speed, the observations so that we come from the past.
Looking farther and farther, we see objects as they were in the past, in an era of increasingly close to the Big Bang. Since light travels at the same speed in all directions, all observers of the universe live in the center of their observable universe.
The universe by definition contains everything that exists, including the space-time, so it has no "edge". Indeed, the existence of an edge implies that beyond this edge, it would not be in the universe, this concept is not intuitive.

Image: View of the Universe in infrared light. This image reveals 1.6 million galaxies among the tens of millions of its local structure. (source: Center / Caltech and the University of Massachusetts).

 View of the Universe in infrared light. galactic clusters

Wilkinson Microwave Anisotropy Probe or WMAP


Wilkinson Microwave Anisotropy Probe (WMAP) was launched June 30, 2001. It is intended to study the anisotropy i.e. the direction of the CMB. WMAP was named in tribute to the American astronomer David Wilkinson, member of the team in charge of the satellite, a pioneer in the study of cosmic microwave background, who died Sept. 5, 2002. The purpose of the mission is to map the best possible accuracy with the temperature fluctuations of the cosmic microwave thermal radiation and its polarization to allow recovery of the material content of the universe. The first results of the WMAP probe have been rightly hailed as a breakthrough in understanding the universe because WMAP produced the first complete map of the CMB from that of the COBE satellite in 1992 and it has a resolution significantly better. The cosmos is older than 13.7 billion years. The first generations of stars have begun to turn 200 million years after the Big Bang.
The image was published February 11, 2003. This picture shows a map of the Universe in the state it was in his establishment, at the age of 380 000 years as it became transparent.


This murmur radio captured in the 3K radiation or -270°Celsius, shows the residual fluctuations of our universe and filigree, lumps of matter that gave rise to galaxies.
Planck probe launched in May 2009 took over to explain the history of the Universe.
Its objective is to observe the cosmic microwave background, the radiation emitted 380 000 years after the birth of the universe, which explains why the current temperature of the Universe is 2.7 K.
"By observing this signal, we can go back in time and see the universe as it was there billions of years ago, " explains Dominique Yvon, astrophysicist at the CEA.


Image: The analysis of the WMAP image of the sky, indicates that the universe is older than 13.7 billion years (with an accuracy of 1%), it is composed of 73% dark energy, 23% Cold dark matter, and only 4% of atoms. It is currently expanding at a rate of 71 km/s/Mpc (with an accuracy of 5%). It went through episodes of rapid expansion called inflation and grow forever. Credit: WMAP Science Team, NASA



Space observatory Planck ESA captures the cosmic radiation or cosmic microwave background (CMB). The CMB is the "first light" of the universe, published shortly after the Big Bang, there are about 13.700 billion years, when the light began to travel freely for the first time. The huge fireball that followed the Big Bang has cooled slowly to become a backdrop to microwaves. Planck observes and measures the change in temperature through the microwave background, with a much higher sensitivity, better angular resolution and a wider range of frequencies, all previous observatories. The Planck mission will then show us what the universe looks like through the first light emitted when it was only 380 000 years. On July 3, 2009, Planck reached the L2 Lagrange point and was placed on a course called Lissajous orbit. Planck measure with great precision the cosmic microwave background radiation or CMB (trace of the Big Bang) to establish a mapping of inhomogeneities in temperature and polarization of this radiation.


For that it embeds a telescope of 1.5 m in diameter and 2 scientific instruments developed by the LFI and HFI told Italy to France.
The first images very promising, arrived June 14, 2009. This is the famous image of the Whirlpool Galaxy spiral, M51, that those responsible for the instrument Photoconductor Array Camera and Spectrometer have received, for initial analysis.
The first edition of the catalog of compact sources (ERCSC, Early Release Compact Source Catalogue) has been published and presented 11 January 2011, with thousands of sources detected by Planck.

 The first results of Planck

Image: First results of Planck were unveiled at an international conference held in Paris in January 2011. Image noise in the infrared cosmic background.
Credit: Planck Collaboration

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