A research team headed by College of Charleston astrophysicist Jon Hakkila has discovered a peculiarity in the light curves of astronomical phenomena called gamma-ray bursts that may provide a breakthrough in understanding the conditions that produce these events.
An artist’s impression of a gamma-ray burst’s jet. Image credit: S. Wiessinger / NASA’s Goddard Space Flight Center.
Gamma-ray bursts (GRBs) are the intrinsically brightest explosions known in the Universe.
These events last from seconds to minutes, and originate during the formation of a black hole accompanying a beamed supernova or colliding neutron stars.
The narrow beam of intense GRB radiation can only be seen when the jet points toward Earth, but such an event can be seen across the breadth of the Universe.
Dr. Hakkila and co-authors analyzed four very bright gamma-ray bursts (single-pulsed GRBs 910601 and 960924 and double-pulsed GRBs 910503 and 990104B).
The researchers used data collected by the Burst and Transient Source Experiment (BATSE), a high energy astrophysics experiment on NASA’s Compton Gamma-Ray Observatory.
They discovered that the pulses composing these GRBs exhibited complex, time-reversible wavelike structures.
In other words, each GRB pulse shows an event in which time appeared to repeat itself backwards.
“We 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,” Dr. Hakkila said.
“Only the brightest GRB pulse light curves exhibit the time-reversed wavelike structures.”
“The time-reversible light curves do not necessarily violate natural laws of cause and effect,” he added.
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 in that it does not appear to have been predicted by theoretical models,” Dr. Hakkila said.
“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.”
The study will be published in the Astrophysical Journal.
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Jon Hakkila et al. 2018. Smoke and Mirrors: Signal-to-Noise and Time-Reversed Structures in Gamma-Ray Burst Pulse Light Curves. ApJ, in press; arXiv: 1804.10130
