A giant outburst of a rare dead star has occurred in a nearby galaxy.
This in itself may not be all that strange; but for the first time, changes in its brightness during this event have been well documented, giving scientists the opportunity to understand the processes that cause these colossal flares.
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). The sun does in 100 millennia.
“Even in an inactive state, magnetars can be a hundred thousand times brighter than our Sun, but in the case of the flare we studied – GRB 2001415 – the released energy is equivalent to that which our Sun emits for a hundred thousand years,” said astrophysicist Alberto J. Castro- Tirado of the Institute of Astrophysics of Andalusia in Spain.
All stars have their own quirks and characteristics, but magnetars should be close to the most unusual. These are neutron stars that are already awe-inspiring – the collapsed, dead cores of once massive stars, roughly 2.3 times the mass of the Sun, packed into a superdense sphere just 20 kilometers (12.4 miles) across.
What the magnetar brings to the table is the magnetic field of absolutely crackers. These magnetic structures are about 1000 times more powerful than that of a typical neutron star, and a quadrillion times more powerful than that of Earth, and we do not know how or why they formed.
We know they lead to some pretty interesting behavior not seen in ordinary neutron stars. The internal pressure of gravity competes with the external attraction of the magnetic field, resulting in unpredictable and powerful magnetic earthquakes. Scientists now believe these quakes are the strongest contenders for mysterious signals known as fast radio bursts, emitting more radio energy in milliseconds than 500 million Suns.
But these earthquakes are volatile, unpredictable, which means that they are difficult to observe and characterize. April 15, 2020, when a device on the International Space Station, designed to observe the earth’s atmosphere, detected something much more distant. It was an event called GRB 2001415, a gamma-ray burst emitted by what was later found to be a magnetar in another galaxy.
Now, using artificial intelligence, the team led by Castro-Tirado analyzed the eruption in detail, accurately measuring the fluctuations in brightness produced by the magnetar during the eruption.
“The difficulty lies in the brevity of the signal, the amplitude of which quickly decays and mixes with the background noise. And since this is a correlated noise, its signal is difficult to distinguish, ”explained astrophysicist Victor Reglero from the University of Valencia in Spain. …
“The intelligence we developed at the University of Valencia has allowed this impressive phenomenon, together with sophisticated data analysis techniques, to be discovered.”
According to the team’s analysis, the wobbles are consistent with Alfvén waves in the magnetar’s magnetosphere, caused by an earthquake in the earth’s crust. These waves bounce back and forth between the traces of their magnetic field lines, releasing energy as they interact in a process called magnetic reconnection, which we know leads to flares in our own star.
By measuring the fluctuations, the team determined that the volume of the eruption of the magnetar was equal in magnitude or even greater than the volume of the magnetar itself. This is damn spectacular, especially considering the cosmic chasm the radiation passed through. This is the most distant magnetar for which such an eruption has been observed.
“In the future, the magnetar seemed to want to show us its existence from its cosmic loneliness, singing in kHz with the power of Pavarotti of a billion suns,” said Reglero. “A real space monster!”
The team’s research was published in Nature…
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