THE SHORT, VIOLENT LIVES OF MAGNETARS
On December 27, 2004, Earth’s atmosphere shook with the impact of a cosmic blast. The thin air high above the surface reverberated under the assault, the radiation setting off a cascade of ionisation deep into the atmosphere. The Burst Alert Telescope aboard the newly launched Neil Gehrels Swift Observatory satellite, designed to detect the most powerful explosions in the universe, was saturated with high-energy photons.
The culprit behind this colossal event wasn’t a supernova or even a collision between two dead stars, like the type seen by LIGO and Virgo (see page 28). Instead, it was a burst of gamma rays from a magnetar: the collapsed core of a dead star known as a neutron star, but one with extreme and tangled magnetic fields. And unlike with supernovae or gravitational-wave-producing collisions, the star survived to flash again.
This object, known as SGR 1806-20, is located roughly 50,000 light-years away within our own galaxy. The thicker air in Earth’s lower atmosphere shielded us from the worst of its radiation, so none of us surface-dwellers saw or felt anything on that day. However, gamma-ray observatories, radio telescopes and atmospheric observers all saw SGR 1806-20. The sheer magnitude of the blast — dumping as much energy into space in a tenth of a second as the Sun emits in 150,000 years — shows how powerful magnetars are. Their magnetic fields are approximately a quadrillion (10 ) times that of the Sun, and 1,000 times greater than the fields generated by typical neutron
