Deflecting light from the Big Bang.
Using a telescope in Antarctica and ESA's Herschel space observatory, astronomers have made the first detection of a subtle twist in the relic radiation from the Big Bang, paving the way towards revealing the first moments of the Universe's existence.
The elusive signal was found in the way the first light in the Universe has been deflected during its journey to Earth by intervening galaxy clusters and dark matter, an invisible substance that is detected only indirectly through its gravitational influence.
The discovery points the way towards finding evidence for gravitational waves born during the Universe's rapid 'inflation' phase, a crucial result keenly anticipated from ESA's Planck mission.
The relic radiation from the Big Bang - the Cosmic Microwave Background, or CMB - was imprinted on the sky when the Universe was just 380 000 years old. Today, some 13.8 billion years later, we see it as a sky filled with radio waves at a temperature of just 2.7 degrees above absolute zero.
Tiny variations in this temperature - around a few tens of millionths of a degree - reveal density fluctuations in the early Universe corresponding to the seeds of galaxies and stars we see today. The most detailed all-sky map of temperature variations in the background was revealed by Planck in March.
But the CMB also contains a wealth of other information. A small fraction of the light is polarised, like the light we can see using polarised glasses. This polarised light has two distinct patterns: E-modes and B-modes.
E-modes were first found in 2002 with a ground-based telescope. B-modes, however, are potentially much more exciting to cosmologists, although much harder to detect.
They can arise in two ways. The first involves adding a twist to the light as it crosses the Universe and is deflected by galaxies and dark matter - a phenomenon known as gravitational lensing.
The second has its roots buried deep in the mechanics of a very rapid phase of enormous expansion of the Universe, which cosmologists believe happened just a tiny fraction of a second after the Big Bang - 'inflation'.
The new study has combined data from the South Pole Telescope and Herschel to make the first detection of B-mode polarisation in the CMB due to gravitational lensing.
"This measurement was made possible by a clever and unique combination of ground-based observations from the South Pole Telescope - which measured the light from the Big Bang - with space-based observations from Herschel, which is sensitive to the galaxies that trace the dark matter which caused the gravitational lensing," says Joaquin Vieira, of the California Institute of Technology and the University of Illinois at Urbana-Champaign, who led the Herschel survey used in the study.