Using a unique polaroid camera attached to the Liverpool Telescope to observe a gamma-ray burst, astronomers have determined that strong magnetic fields are responsible for beaming the light towards Earth.

Gamma-ray bursts (GRBs) occur when the core of a massive star collapses or two neutron stars merge together, both of which result in a powerful explosion visible as an intense burst of light. One such GRB – 090102 – was detected by NASA's Swift satellite on 2 January 2009; its evolution was subsequently tracked by ground-based telescopes all over the world.

The robotic Liverpool Telescope based at La Palma observed the varying brightness of the GRB using a camera made from a spinning disk of polaroid. This allowed the magnetic field of the burst to be measured; the first time that such a measurement had been made within a few minutes of the stellar explosion.

The team discovered that the GRB emitted a well-ordered magnetic field. “Theoreticians predicted that such a magnetic field is generated in the central fireball and accelerates GRB jets to almost the speed of light,” says Shiho Kobayashi. “Now the existence of strong magnetic fields has been shown to be correct.”

The observations raise the suggestion that GRBs are powered and collimated by organised electromagnetic fields, and the team hope to find more evidence for this process occurring in other GRBs.

“This important result gives us new insight into the physics of these remarkable objects and is a testament to the close collaboration between observers, theoreticians and technologists in the Liverpool and NASA Swift teams,” adds Carole Mundell, Leader of the Liverpool John Moores University (LJMU) GRB team. “It’s incredible to think that the GRB discovery and our measurement process – from first detection and notification by NASA’s Swift satellite to the polarization measurement using RINGO on the Liverpool Telescope – took place completely automatically within less than three minutes and with no human intervention!”

The results of the LJMU team are presented in the 10 December issue of Nature.