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The expected opacity of the intergalactic space limits the mean free path ofTeV gamma rays to dozens of Megaparsecs. However, TeV photons from numerousmore distant sources have been detected. This might be interpreted, in eachparticular case, in terms of hardening of the emitted spectrum caused bypresently unknown mechanisms at work in the sources. Here we show that thisinterpretation is not supported by the analysis of the ensemble of all observedsources. In the frameworks of an infrared-background model with the lowestopacity, we reconstruct the emitted spectra of distant blazars and find thatupward spectral breaks appear precisely at those energies where absorptioneffects are essential. Since these energies are very different for similarsources located at various distances, we conclude that the breaks are artefactsof the incorrect account of absorption and, therefore, the opacity of theUniverse for gamma rays is overestimated even in the most conservative model.This implies that some novel physical or astrophysical phenomena should affectlong-distance propagation of gamma rays. A scenario in which a part ofenergetic photons is converted to an inert new particle in the vicinity of thesource and reconverts back close to the observer does not contradict to ourresults. [abridged]

Breaks in gamma-ray spectra of distant blazars and transparency of the Universe