In a nearby galaxy, a rare type of dead star erupted in a giant explosion.
That in itself is perhaps not so special; but, for the first time, the changes in its brightness during this event have been documented in detail, giving scientists a window to understand the processes that produce these colossal eruptions.
The star is a type of extreme neutron star called a magnetar, located up to 13 million light-years away in the Silver Coin Galaxy (NGC 253), and at the peak of 160 milliseconds of its eruption, it emitted as much energy as the Sun in 100 millennia.
“Even in the inactive state, magnetars can be a hundred thousand times brighter than our Sun, but in the case of the flash we studied – the GRB 2001415 – the energy that was released is equivalent to that of our Sun shines in a hundred thousand years “, said astrophysicist Alberto J. Castro-Tirado of the Institute of Astrophysics of Andalusia in Spain.
All stars have their quirks and peculiarities, but magnetars must be close to the most particular. These are neutron stars, which are already fascinating – the collapsed dead nuclei of once massive stars, up to about 2.3 times the mass of the Sun, crammed into an ultra-dense sphere of just 20 kilometers (12.4 miles) of diameter.
What a magnetar brings to the table is an absolutely crisp magnetic field. These magnetic structures are about 1,000 times more powerful than those of a typical neutron star, and a a trillion times more powerful than that of Earth, and we do not know how or why they are formed.
We know that they lead to some pretty interesting behaviors that you don’t see in medium neutron stars. The inward pressure of gravity rivals the outward pull of the magnetic field, resulting in unpredictable and powerful magnetar earthquakes. These earthquakes, scientists now believe, are the main competitor of the mysterious signals known as rapid radio bursts, emitting, in milliseconds, more radio energy than 500 million suns.
But these earthquakes are erratic, unpredictable, which means they have been difficult to observe and characterize. On April 15, 2020, when an International Space Station instrument designed to monitor Earth’s atmosphere picked up something much more distant. This was the event called GRB 2001415, an emitted gamma-ray burst, it was later determined, by a magnetar in another galaxy.
Now, using artificial intelligence, a team led by Castro-Tirado analyzed the eruption in detail, precisely measuring the oscillations of brightness produced by the magnetar during the eruption.
“The difficulty lies in the brevity of the signal, the amplitude of which decreases rapidly and becomes embedded in the background noise. And, since it is correlated noise, it is difficult to distinguish its signal”, explained astrophysicist Victor Reglero of the University of Valencia in Spain.
“The intelligence of the system that we have developed at the University of Valencia is what made it possible, with sophisticated data analysis techniques, to detect this spectacular phenomenon.”
According to the team’s analysis, the oscillations are consistent with The waves of AlfvÃ©n in the magnetosphere of the magnetar triggered by an earthquake in the crust. These waves bounce between the imprints of their magnetic field lines, releasing energy as they interact in a process called magnetic reconnection, which we know causes eruptions in our own star.
By measuring the oscillations, the team determined that the volume of the magnetar eruption was, in magnitude, equal to or even greater than the volume of the magnetar itself. It’s pretty spectacular, especially given the space chasm the show has traveled through. It is the most distant magnetar for which such an eruption has been observed.
“Seen in perspective, it was as if the magnetar wanted to indicate to us its existence from its cosmic solitude, singing in kHz with the force of a Pavarotti of a billion suns”, Reglero said. “A real cosmic monster!”
The team’s research has been published in Nature.