A team of astronomers, including two researchers from UCL’s Mullard Space Science Laboratory, have discovered that a curious dead star has been hiding one of the strongest magnetic fields in the Universe, despite earlier suggestions of an unusually low magnetic field. The discovery was made using Europe’s XMM-Newton space telescope

The object, known as SGR 0418+5729 (or SGR 0418 for short), is a magnetar, a particular kind of neutron star

A neutron star is the dead core of a once massive star that collapsed in on itself after burning up all its fuel and exploding in a dramatic supernova event. They are extraordinarily dense objects, packing more than the mass of our Sun into a sphere only some 20 km across - about the size of a city

A small proportion of neutron stars form and live briefly as magnetars, named for their extremely intense magnetic fields, billions to trillions of times greater than those generated in hospital MRI machines, for example. These fields cause magnetars to erupt sporadically with bursts of high-energy radiation

SGR 0418 lies in our galaxy, about 6,500 light-years from Earth. It was first detected in June 2009 by space telescopes including NASA’s Fermi and Roscosmos’ Koronas-Photon when it suddenly lit up in X-rays and soft gamma rays. It has been studied subsequently by a fleet of observatories, including XMM-Newton

Magnetars spin more slowly than neutron stars, but still complete a rotation within a few seconds. The normal way of determining the magnetic field of a magnetar is to measure the rate at which the spin is declining. Three years of observations of SGR 0418 had led astronomers to infer a weak magnetic field

The team using XMM-Newton used a new technique of searching for variations in the X-ray spectrum of the magnetar over extremely short time intervals as it rotates. This method allowed them to analyze the magnetic field in much more detail and has revealed SGR 0418 as a true magnetic monster

A simple analogy can be made with localized magnetic fields anchored in sunspots on the Sun, where a change in configuration can suddenly lead to their collapse and the production of a flare or, in the case of SGR 0418, a burst of X-rays

UK Space Agency