The more we learn about gravitational lensing, the more it becomes clear how pervasive the phenomenon must be as mass and spacetime interact throughout the cosmos. The most recent findings produced by lensing effects now limn structures so large that they dwarf the galaxy we reside in. Recently detected dark matter filaments, up to 270 million light years in size, are 2000 times the size of the Milky Way, yet would remain unobserved were it not for advanced lensing investigative techniques.
The astronomers behind this work, using data from the Canada-France-Hawaii Telescope Legacy Survey, took advantage of the fact that dark matter should deflect the light from distant galaxies as it travels towards us. The careful measurement of these often tiny effects required the development of new tools for image analysis, but these apparent filaments, sheets and clusters of dark matter seem to gibe with previous theoretical estimates. “Our observations extend the knowledge about the cosmic web far beyond what was known before,” says Liping Fu (Institut d’Astrophysique de Paris). “We confirmed that our model about the Universe is correct even on those very large scales.”
The model Fu is talking about is a paradigm of dark matter that sees galactic clusters and galaxies themselves embedded in the filamentary structures described above. The detection of such structures supports the evolving paradigm; had the filaments not been found, dark matter would be due for a profound re-thinking. Up until now, the observation of gravitational lensing at these weak levels had proven impossible.
Up next: Whole-sky surveys to further study dark matter distribution, probing whether its signature (and that of dark energy) can be explained by modifications to General Relativity. If not, then we do seem to be dealing with a new type of matter and source of energy. Either way, the advance in knowledge will be extraordinary. The paper is Fu, Semboloni et al., “Very weak lensing in the CFHTLS wide: cosmology from cosmic shear in the linear regime,” accepted by Astronomy & Astrophysics and available online.