New cosmic background radiation map challenges some foundations of cosmology

March 22, 2013

Cosmic microwave background seen by Planck space telescope (credit: ESA)

The most detailed map ever created of the cosmic microwave background — the relic radiation from the Big Bang — acquired by ESA’s Planck space telescope, has been released, revealing features that challenge the foundations of our current understanding of the Universe and may require new physics.

  • The fluctuations in the CMB temperatures at large angular scales do not match those predicted by the standard model in physics — their signals are not as strong as expected from the smaller scale structure revealed by Planck.
  • An asymmetry in the average temperatures on opposite hemispheres of the sky runs counter to the prediction made by the standard model that the Universe should be broadly similar in any direction we look.
  • A cold spot extends over a patch of sky that is much larger than expected.
  • Dark energy, a mysterious force thought to be responsible for accelerating the expansion of the Universe, accounts for less than previously thought.

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.

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 kilometers 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.

The cosmic microwave background

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 analyzing 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.

“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.

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.