Polarized light reveals hidden jets of a gamma-ray burst

The dome containing the 2-meter robotic Liverpool Telescope. This instrument can track minute-by-minute changes in the polarization of light emitted in gamma-ray bursts, the violent deaths of massive stars.

Elme (Flickr)

Long-duration gamma-ray bursts (GRBs) are thought to be the energetic explosions of very massive stars, visible from billions of light years away. Thanks to a wealth of observations over the last decade, astronomers are piecing together details of these supernovae, including some surprises that may force us to revise and improve details in theoretical models.

Case in point: Carole G. Mundell and colleagues found the tell-tale signs of strong magnetic fields in a GRB that lingered as the explosion began to fade. Sustaining such magnetic fields requires rapidly moving charged particles in a steady jet—jets that had been thought to give way to random fluctuations from hot plasma. This observation required monitoring minute-by-minute changes in polarized light emitted from the GRB's afterglow, providing details never seen before in these violent astronomical events.

Though long-duration GRBs are associated with very energetic supernovae, the specific manner of their explosion is uncertain. (Short-duration GRBs, by contrast, are likely collisions between neutron stars.) Part of the problem is GRBs' extreme distance: the huge stars necessary to generate them were far more common when the Universe was young, so few GRBs are close enough to allow detailed observations.