Scientists have resolved a longstanding mystery about some of the biggest explosions in the universe, known as gamma-ray bursts (GRBs), according to a new study.
These colossal eruptions are a result of violent cosmic events, such as the deaths of massive stars, and they are so luminous that they can outshine entire galaxies for short periods of time.
Scientists have been able to study the light emitted by GRBs hours or days after they blew up, but it is much more challenging to observe light from the earliest post-blast moments, which contains valuable information about the initial mechanics of these brilliant events.
Now, a team led by Nuria Jordana-Mitjans, a PhD student at the University of Bath, has managed to capture light emitted just 90 seconds after the onset of GRB 141220A, which was detected in December 2014.
The observations represent the “earliest-ever detection” of polarization patterns embedded in optical light from a GRB’s “forward shock,” an energy wave that propagates out from the explosion to produce a long-lived afterglow, according to a study published on Wednesday in the Monthly Notices of the Royal Astronomical Society.
The observations reveal the signature of the primordial magnetic fields that shape GRBs in the seconds and minutes after they erupt. The neatly polarized magnetic fields are predicted to exist for a short period before getting blown apart as the forward shock crashes into stellar debris that has been shaken off by the supernova, creating a scrambled tangle of field lines that can be seen in the unpolarized afterglow.
These predictions have been challenged by studies that report the survival of ordered polarized light at longer timescales, causing “the nature of very early-time polarization properties of forward shocks” to remain “debated,” according to the new study.
Jordana-Mitjans and her colleagues believe that they have resolved this debate with an in-depth analysis of early light from GRB 141220A captured by the autonomous robotic Liverpool Telescope, which is outfitted with intelligent software as well as a specialized polarimeter instrument called RINGO3.
Their results confirm the short-lived nature of these ordered magnetic fields “as theoretically predicted for forward shocks and consistent with previous detections of low degrees of optical polarization in GRB afterglows observed hours to days after the burst,” report the authors in the study.
"This new study builds on our research that has shown the most powerful GRBs can be powered by large-scale ordered magnetic fields, but only the fastest telescopes will catch a glimpse of their characteristic polarization signal before they are lost to the blast," Jordana-Mitjans said in a statement.
The results shed new light on the immediate aftermath of these ultra-luminous explosions, which have remained persistently out-of-reach to telescopes for decades. GRB researchers around the world hope that next generation observatories, such as the Cherenkov Telescope Array, will capture even more of these bursts early in their development, which will help to unravel the many remaining mysteries about the origin and dynamics of these blinding cosmic spectacles.