Planck telescope peers into the primordial Universe

ORIGINAL: Nature

Mark Peplow

21 March 2013 

Analysis of cosmic microwave background backs sudden ‘inflation’ after Big Bang. 

The Planck space telescope's view of the cosmic background radiation is helping to reveal details about the birth of the Universe. ESA/PLANCK COLLABORATION 

The Planck space telescope has delivered the most detailed picture yet of the cosmic microwave background, the residual glow of the Big Bang. 

Scientists unveiling the results from the €600 million European Space Agency (ESA) probe said that they shed fresh light on the first instants of our Universe’s birth. They also peg the age of the Universe at 13.81 billion years — slightly older than previously estimated. 

“For cosmologists, this map is a goldmine of information,” says George Efstathiou, director of the Kavli Institute for Cosmology at the University of Cambridge, UK, one of Planck’s lead researchers. 

Planck’s results strongly support the idea that in the 10-32 seconds or so after the Big Bang, the Universe expanded at a staggering rate — a process dubbed inflation. 

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Cosmology: The test of inflation

Inflation would explain why the Universe is so big, and why we cannot detect any curvature in the fabric of space (other than the tiny indentations caused by massive objects like black holes). The sudden ballooning of the primordial Universe also amplified quantum fluctuations into clumps of matter that later seeded the first stars, and eventually the straggly superclusters of galaxies that span hundreds of millions of light years. 

The cosmic microwave background (CMB) radiation studied by Planck dates from about 380,000 years after the Big Bang, when the Universe had cooled to a few thousand degrees and neutral atoms of hydrogen and helium began to form from the seething mass of charged plasma. That allowed photons to travel unimpeded through space, in a pattern that carried the echoes of inflation. Those photons are still out there today, as a dim glow of microwaves with a temperature of just 2.7 K. 

Since the CMB was first detected in 1965, the Cosmic Background Explorer (COBE) and the Wilkinson Microwave Anisotropy Probe (WMAP) have mapped the tiny temperature variations in the CMB with ever more precision. This has enabled cosmologists to work out when the Big Bang happened, estimate the amount of unseen dark matter in the cosmos, and measure the ‘dark energy’ that is accelerating the expansion of the Universe. 

Planck, launched in 2009, is more than three times more sensitive than its predecessor WMAP. Its high-frequency microwave detector is cooled to just 0.1 degrees above absolute zero. That enables it to detect variations in the temperature of the CMB as small as a millionth of a degree. 

These precision measurements show that the Universe is expanding slightly slower than estimated by WMAP. That rate, known as the Hubble constant, is 67.3 kilometres per second per megaparsec, which suggests that the Universe is about 80 million years older than WMAP had calculated. 

It also means that dark energy makes up 68.3% of the energy density of the Universe, a slightly smaller proportion than WMAP had estimated. The contribution of dark matter swells from 22.7% to 26.8%, leaving normal matter making up less than 5%. 

Planck also confirmed some oddities earlier noted by WMAP. The simplest models of inflation predict that fluctuations in the CMB should look the same all over the sky. But WMAP has found, and Planck confirmed, an asymmetry between opposite hemispheres of the sky, as well as a ‘cold spot’ that covers a large area. The asymmetry “defines a preferred direction in space, which is an extremely strange result,” says Efstathiou. This rules out some models of inflation, but does not undermine the idea itself, he adds. It does, however, raise tantalizing hints that there may yet be new physics to be discovered in Planck’s data. 

So far, the team have analysed about 15.5 months of data, and “we have about as much again to look at”, says Efstathiou. The team expects to release their next tranche of data in early 2014. Nature doi:10.1038/nature.2013.12658