We saw one of the most powerful magnets in the Universe come to life – and our theories can’t quite explain it

By Marcus Lower, CSIRO, Gregory Desvignes, Max Planck Institute for Radio Astronomy, Patrick Weltevrede, University of Manchester

After a decade of silence, one of the most powerful magnets in the universe suddenly burst back to life in late 2018. The reawakening of this “magnetar”, a city-sized star named XTE J1810-197 born from a supernova explosion, was an incredibly violent affair.

The snapping and untwisting of the tangled magnetic field released enormous amounts of energy as gamma rays, X-rays and radio waves.

By catching magnetar outbursts like this in action, astronomers are beginning to understand what drives their erratic behaviour. We are also finding potential links to enigmatic flashes of radio light seen from distant galaxies known as fast radio bursts.

In two new pieces of research published in Nature Astronomy, we used three of the world’s largest radio telescopes to capture a host of never before seen changes in the radio waves emitted by one of these rare objects in unprecedented detail.

Magnetic monsters

Magnetars are young neutron stars, with magnetic fields billions of times stronger than our most powerful Earth-based magnets. The slow decay of their magnetic fields creates an enormous amount of stress in their hard outer crust until it eventually fractures. This twists the magnetic field and releases large amounts of energetic X-rays and gamma rays as it unwinds.

These exotic stars were initially detected back in 1979 when an intense gamma-ray burst emitted by one was picked up by spacecraft across the Solar System. Since then, we’ve found another 30 magnetars, the vast majority of which have only been detected as sources of X-rays and gamma rays. However, a rare few have since been found to also emit flashes of radio waves.

The first of these “radio-loud” magnetars goes by the name XTE J1810-197. Astronomers initially discovered it as a bright source of X-rays after an outburst in 2003, then found it emitted bright pulses of radio waves as it rotated every 5.54 seconds.

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