With our skies being full of so many wonders, it’s daunting to imagine what is happening when nobody's looking. That’s why astronomers were thrilled when a satellite happened to be facing the right way at the right time when a rare explosion in space happened.
The giant eruption lit up a whole galaxy, known as M82, 12 million light years away from Earth. Thinking two colliding neutron stars may have caused the explosion, astronomers immediately searched for an afterglow – but there wasn’t one. They realised this intense gamma-ray burst must have come from a single, super-powerful neutron star.
Neutron stars are the remains of massive stars, which are eight times more massive than the Sun, after they explode in a supernova. Instead of turning into a black hole, the remains form very compact spheres with strong magnetic fields.
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But the observed neutron star’s magnetic fields are super-strong, making it a magnetar: an extremely magnetic neutron star. With magnetic fields over 10,000 stronger than average neutron stars, magnetars have the strongest magnetic fields measured in the whole Universe and emit energy through giant flares.
It was one of these extra-galactic flares that ESA’s satellite INTEGRAL happened to capture in November 2023. The burst only lasted a mere one-tenth of a second – but within 13 seconds a gamma-ray burst alert was sent to astronomers worldwide.
“We immediately realised that this was a special alert. Gamma-ray bursts come from far away and anywhere in the sky, but this burst came from a bright nearby galaxy,” said Dr Sandro Mereghetti of the National Institute for Astrophysics, Italy, lead author of the study published in journal Nature.
Mereghetti’s team took Earth- and space-based telescope observations straight away, but they didn’t pick up any signals of visible light, X-rays, or gravitational waves. INTEGRAL had captured a uniquely and transient moment that left no traces.
Without these traces, the most likely answer behind the explosion is the mega-magnetic neutron explanation – making this the first confirmation of a magnetar flare outside the Milky Way.
In the past 50 years, scientists have identified only three giant flares as originating from a magnetar in our galaxy. One, in 2004, was so strong that it affected Earth’s upper atmosphere in the same way Solar flares do.
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