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From www.esa.int
Planck Reveals Almost Perfect Universe
21 March 2013
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| Cosmic microwave background seen by Planck. . |
Acquired by ESA’s Planck space telescope, the most detailed map ever created
of the cosmic microwave background – the relic radiation from the Big Bang –
was released today revealing the existence of features that challenge the
foundations of our current understanding of the Universe.
The image is based on the initial 15.5 months of data from Planck and is the
mission’s first all-sky picture of the oldest light in our Universe, imprinted on the
sky when it was just 380 000 years old.
At that time, the young Universe was filled with a hot dense soup of interacting
protons, electrons and photons at about 2700ºC. When the protons and
electrons joined to form hydrogen atoms, the light was set free. As the
Universe has expanded, this light today has been stretched out to microwave
wavelengths, equivalent to a temperature of just 2.7 degrees above absolute
zero.
This ‘cosmic microwave background’ – CMB – shows tiny temperature
fluctuations that correspond to regions of slightly different densities at very
early times, representing the seeds of all future structure: the stars and
galaxies of today.
According to the standard model of cosmology, the fluctuations arose
immediately after the Big Bang and were stretched to cosmologically large
scales during a brief period of accelerated expansion known as inflation.
Planck was designed to map these fluctuations across the whole sky with
greater resolution and sensitivity than ever before. By analysing the nature and
distribution of the seeds in Planck’s CMB image, we can determine the
composition and evolution of the Universe from its birth to the present day.
Planck’s anomalous sky
Overall, the information extracted from Planck’s new map provides an excellent
confirmation of the standard model of cosmology at an unprecedented
accuracy, setting a new benchmark in our manifest of the contents of the
Universe.
But because precision of Planck’s map is so high, it also made it possible to
reveal some peculiar unexplained features that may well require new physics to
be understood.
“The extraordinary quality of Planck’s portrait of the infant Universe allows us to
peel back its layers to the very foundations, revealing that our blueprint of the
cosmos is far from complete. Such discoveries were made possible by the
unique technologies developed for that purpose by European industry,” says
Jean-Jacques Dordain, ESA’s Director General.
“Since the release of Planck’s first all-sky image in 2010, we have been
carefully extracting and analysing all of the foreground emissions that lie
between us and the Universe’s first light, revealing the cosmic microwave
background in the greatest detail yet,” adds George Efstathiou of the University
of Cambridge, UK.
One of the most surprising findings is that the fluctuations in the CMB
temperatures at large angular scales do not match those predicted by the
standard model – their signals are not as strong as expected from the smaller
scale structure revealed by Planck.
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| Asymmetry and cold spot. . |
Another is an asymmetry in the average temperatures on opposite
hemispheres of the sky. This runs counter to the prediction made by the
standard model that the Universe should be broadly similar in any direction we
look.
Furthermore, a cold spot extends over a patch of sky that is much larger than
expected.
The asymmetry and the cold spot had already been hinted at with Planck’s
predecessor, NASA’s WMAP mission, but were largely ignored because of
lingering doubts about their cosmic origin.
“The fact that Planck has made such a significant detection of these anomalies
erases any doubts about their reality; it can no longer be said that they are
artefacts of the measurements. They are real and we have to look for a
credible explanation,” says Paolo Natoli of the University of Ferrara, Italy.
“Imagine investigating the foundations of a house and finding that parts of
them are weak. You might not know whether the weaknesses will eventually
topple the house, but you’d probably start looking for ways to reinforce it pretty
quickly all the same,” adds François Bouchet of the Institut d’Astrophysique de
Paris.
One way to explain the anomalies is to propose that the Universe is in fact not
the same in all directions on a larger scale than we can observe. In this
scenario, the light rays from the CMB may have taken a more complicated
route through the Universe than previously understood, resulting in some of the
unusual patterns observed today.
“Our ultimate goal would be to construct a new model that predicts the
anomalies and links them together. But these are early days; so far, we don’t
know whether this is possible and what type of new physics might be needed.
And that’s exciting,” says Professor Efstathiou.
New Cosmic Recipe
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| New Cosmic Recipe. . |
Beyond the anomalies, however, the Planck data conform spectacularly well to
the expectations of a rather simple model of the Universe, allowing scientists to
extract the most refined values yet for its ingredients.
Normal matter that makes up stars and galaxies contributes just 4.9% of the
mass/energy density of the Universe. Dark matter, which has thus far only
been detected indirectly by its gravitational influence, makes up 26.8%, nearly
a fifth more than the previous estimate.
Conversely, dark energy, a mysterious force thought to be responsible for
accelerating the expansion of the Universe, accounts for less than previously
thought.
Finally, the Planck data also set a new value for the rate at which the Universe
is expanding today, known as the Hubble constant. At 67.15 kilometres per
second per megaparsec, this is significantly less than the current standard value
in astronomy. The data imply that the age of the Universe is 13.82 billion years.
“With the most accurate and detailed maps of the microwave sky ever made,
Planck is painting a new picture of the Universe that is pushing us to the limits
of understanding current cosmological theories,” says Jan Tauber, ESA’s Planck
Project Scientist.
“We see an almost perfect fit to the standard model of cosmology, but with
intriguing features that force us to rethink some of our basic assumptions.
“This is the beginning of a new journey and we expect that our continued
analysis of Planck data will help shed light on this conundrum.”
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