Bursts of Light in Space Challenge Theories

Scientists from Liverpool John Moores University's Gamma Ray Burst (GRB) team, along with researchers from across Europe, the United States, Japan, and Australia, have discovered a new kind of signal from a powerful exploding star in the distant universe called Gamma Ray Burst 121024.  The research, led by Dr Klaas Wiersema, of the University of Leicester Department of Physics and Astronomy, has uncovered scientific findings reported in Nature this week, that will change theoretical understandings of the afterglows of GRBs.

"We measured the amount of circular polarisation of the light," explained Professor Carole Mundell, leader of the Liverpool GRB team.

"Although the signal is very small, just 0.6%, theories predict the light should show no circular polarisation," she continued.

“Naturally occurring circularly polarised light on Earth is rare and normally only observed in the light reflected from the luminescence shells of scarab beetles or mantis shrimps and the bioluminescent light from the larvae of fireflies.

“In space, circular polarisation is usually produced when light is scattered by cosmic dust grains. Circular polarisation in Gamma Ray Bursts is unexpected so new theories may have to be developed to explain it.”

Gamma Ray Bursts are the instantaneously most luminous objects in the Universe and are thought to be powered by the collapse of a massive star at the end of its life and the formation of a black hole. A brief but bright flash of high energy gamma rays, detected by satellites orbiting Earth, signals the birth cry of the black hole.

Reporting their results in Nature, the team describe observations made using the 8-metre Very Large Telescope in Chile to measure the properties of the dying embers or the visible light of the fading afterglow four hours after discovery of the explosion.

Co-team member, Dr Andreja Gomboc of the University of Ljubljana and member of the Liverpool GRB team said:

"This measurement shows that it is possible to probe very weak, tangled magnetic fields that exist in the ambient medium around the GRB and into which the expanding blastwave collides, but we hope theorists will develop new models to explain how this polarisation is produced." 

Last year, the Liverpool team announced discovery of the first direct observational evidence of stable, long-lived magnetic fields in a Gamma Ray Burst by measuring large amounts of linear polarisation in the very early afterglow of GRB 120308A, using the novel RINGO2 polarimeter on the robotic Liverpool Telescope just minutes after the explosion.

"Our RINGO2 observations showed that large-scale ordered magnetics fields drive and focus the material ejected in the blast," commented Professor Mundell. "These new observations show that the explosion energy may not be transfered to the surrounding ambient material as efficiently as we expected. New models may be required to understand the complex physics on microscopic scales."

Further Information:

Circular polarization in the optical afterglow of GRB 121024A” Wiersema, K et al.

Published in Nature online and accessible at: http://dx.doi.org/10.1038/nature13237

Photo credit: "NASA's Goddard Space Flight Center/S. Wiessinger

Interviews contact details  

Professor Carole Mundell                           

Astrophysics Research Institute          

Liverpool John Moores University,          

Email:c.mundell@ljmu.ac.uk

Tel. +44 151 231 2917   

+ 44 797 477 9923 (mobile)

Image: Theoretical models link the presence of strong and stable polarized light in a gamma-ray burst's jet with a large-scale magnetic field (a blue spiral, in this illustration) originating from the newly-formed black hole.

Credit: NASA's Goddard Space Flight Center/S. Wiessinger

Clare Coombes, Press and Publications Officer, Liverpool John Moores University, T: 0151 231 3004 press@ljmu.ac.uk 

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