Above – A model of temporally-reversed pulse structure. An impactor (red) produces variable radiation as it travels through axisymmetric, stretched clouds (blue).
They noticed this "mirroring" effect after realizing the "smoke" of limited instrumental sensitivity smeared out GRB light, giving moderately bright pulse light curves a three-peaked appearance and faint pulse light curves the shape of a simple bump. Only the brightest GRB pulse light curves exhibit the time-reversed wavelike structures.
Hakkila says that the time-reversible light curves do not necessarily violate natural laws of cause and effect. The research team believes that the most natural explanation is that a blast wave or a rapidly-ejected clump of particles radiates while being reflected within an expanding GRB jet or while moving through a symmetric distribution of clouds.
This discovery is intriguing, says Hakkila, in that it does not appear to have been predicted by theoretical models. Despite this, the discovery should provide astrophysicists with new tools in understanding the final death throes of massive stars and the physical processes that accompany black hole formation.