Synopsis: Undoing the Effects of Gravitational Lensing
The cosmic microwave background, or CMB, can be thought of as the wallpaper of the observable Universe. Studies of the patterns in this wallpaper tell us about the Universe’s history. But they are complicated by galaxies and other foreground objects that distort our view through the effect of gravitational lensing. New work shows how one can remove these distortions using background light at infrared wavelengths. This first demonstration of so-called delensing could assist future searches for gravitational wave signatures in the CMB.
Over the past few decades, cosmologists have used CMB maps to determine the geometry and density distribution of the Universe. Further studies—particularly focused on the polarization patterns in the CMB—could provide information on gravitational waves thought to originate from the Universe’s rapid expansion after the big bang. However, gravitational lensing by intervening massive objects deflects CMB light, obscuring this polarization signal.
Previous proposals for delensing have suggested using features within the CMB itself to identify where lensing has occurred. Patricia Larsen from the Institute of Astronomy and the Kavli Institute for Cosmology Cambridge, UK, and her colleagues have developed—and tested—a delensing method based on the cosmic infrared background (CIB), which is diffuse light coming primarily from dusty star-forming galaxies. Bright spots in the CIB correspond to regions of high galaxy concentration that should exert an enhanced gravitational lensing effect. Using a CIB map provided by the Planck satellite, the team created a delensing template that they applied to the best full-sky CMB map (also from Planck). The delensed CMB data showed sharper peaks in the spectrum of temperature fluctuations, and this sharpening agrees with theoretical models of gravitational lensing.
This research is published in Physical Review Letters.
Michael Schirber is a Corresponding Editor for Physics based in Lyon, France.