Planck gives earliest snapshot of the Universe

Europe's Planck satellite, a flagship mission for the UK Space Agency, has compiled the most detailed map ever of this leftover radiation – called the cosmic microwave background (CMB). The map gives a picture of how the Universe looked just 380,000 years after the Big Bang and the pattern of temperature fluctuations that were the 'seeds' that started the formation of the galaxies and stars we see today.

The international team behind the mission, including scientists from Oxford University, report results showing that, at 13.82 billion years old, the Universe is slightly older than was thought, that give a more accurate recipe for its composition and the relative amounts of dark matter and dark energy, and that bolster evidence for a mysterious phenomenon called 'inflation'.

'One of the biggest challenges we faced was looking back through the light from all the galaxies and stars born in the last 13 billion years to glimpse the cosmic microwave background, this imprint of the very early Universe,' said Dr Joanna Dunkley of Oxford University's Department of Physics, who led Oxford's Planck research team with Dr Erminia Calabrese and Dr Charmaine Armitage-Caplan.

'Part of the Oxford team's job was to use data from other experiments, such as the Atacama Cosmology Telescope, to 'clean up' the Planck signal and help us see through all the very bright objects, including our own Milky Way, that lie between us and this echo of the ancient Universe,' Dr Dunkley adds.

The properties of the hot and cold regions of the map provide information about the composition and evolution of the Universe. Normal matter that makes up stars and galaxies contributes just 4.9% of the mass/energy density of the Universe. Dark matter, which has so 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 slightly less than previously thought, at around 69%.

The Planck data also set a new value for the rate at which the Universe is expanding today, known as the Hubble constant. At 67.3 km/s/Mpc, this is lower than the value measured from relatively nearby galaxies. This somewhat slower expansion implies that the Universe is also a little older than previously thought, at 13.82 billion years.

The analysis also gives strong support for theories of 'inflation', a very brief but crucial early phase during the first tiny fraction of a second of the Universe's existence. As well as explaining many properties of the Universe as a whole, this initial expansion caused the ripples in the CMB that we see today.

Although this primordial epoch can't be observed directly, the theory predicts a set of very subtle imprints on the CMB map. Previous experiments have not been able to confidently detect these subtle imprints, but the high resolution of Planck's map confirms that the tiny variations in the density of the early Universe match those predicted by inflation.

Dr Dunkley said: 'The sizes of these tiny ripples hold the key to what happened in that first trillionth of a trillionth of a second. Planck has given us striking new evidence that indicates they were created during this incredibly fast expansion, just after the Big Bang. Our results are likely to inspire much more research into this very unusual and mysterious period when space was expanding faster than light.'

But because the precision of Planck's map is so high, it also reveals some peculiar unexplained features. Amongst the most surprising findings are that the fluctuations in the CMB over large scales do not match those predicted by the standard model.

Dr Chris Castelli, Acting Director of Science, Technology and Exploration at the UK Space Agency, said: 'We're immensely proud to be playing a key role in this amazing discovery. With its ability to make such detailed and accurate observations, Planck is helping us to place the vital pieces of a jigsaw that could give us a full picture of the evolution of our Universe, rewriting the textbooks along the way.'