Scientists have now taken a step closer to understanding massive magnetar explosions.
A magnetar is a rare neutron star with the most intense magnetic field. Its magnetic
field is 1,000 times stronger than that of a regular neutron star, and a trillion times
stronger than the Earth's. Only around 30 of these things are known since
it is challenging to detect them with current technology.
While they are known to have violent eruptions, scientists know very little about them because
of their unpredictable nature and short duration of barely tenths of a second.
For the first time, an international group of scientists with outstanding Valencian participation
was able to measure oscillations in the brightness of a magnetar during its most violent moments.
The magnetar, known as GRB2001415, released energy equivalent to that produced by the
sun in 100,000 years in less than a tenth of a second.
The observation was carried out without human intervention, due to an artificial intelligence
system built at the Image Processing Laboratory (IPL) of the University of Valencia.
For the past 20 years, scientists have been wondering if magnetars have high-frequency
oscillations. They measured oscillations in the brightness of the magnetar during its
most violent moments. These episodes are a crucial component in understanding giant magnetar
eruptions. The work was conducted by six researchers
from the University of Valencia and Spanish collaborators.
Magnetars can be 100,000 times more luminous than our sun even when they are dormant.
The magnetar's explosion, which lasted about a tenth of a second, was discovered on April
15th, 2020, amid the pandemic. Since then, the researchers have been doing
a lot of data analysis work because it was a 10 by 16 Gauss neutron star and located
in another galaxy. This is a truly cosmic beast.
Scientists believe that magnetar eruptions are caused by instabilities in their magnetospheres
or a type of "earthquake" that occurs in their crust, a rigid and elastic layer around a
kilometer thick. Regardless of the trigger, a type of wave
known as the Alfvén is formed in the star's magnetosphere, which interacts with each other,
dissipating energy. According to the study, the oscillations spotted
in the eruption are consistent with the emission created by the interaction of Alfvén waves,
whose energy is quickly absorbed by the crust. The magnetic reconnection process, and the
pulses identified in the magnetar, ends in a few moments, fading 3.5 milliseconds after
the main burst. The ASIM sensor, which is onboard the International
Space Station (ISS), detected the eruption. ASIM was the only one of the seven telescopes
able to register the main phase of the eruption in its full energy range without experiencing
saturation. The scientific team was able to solve the
event's temporal structure, a genuinely complex mission that took more than a year of research
for only two seconds during which the data was collected.
Signal analysis was quite a challenge in detecting quasi-periodic oscillations in GRB2001415.
The problem arises from the shortness of the signal, whose amplitude rapidly decays and
becomes implanted in background noise. It is also tough to distinguish its signal because
of its associated noise. Even though these eruptions had already been
detected in two of the 30 known magnetars in the galaxy and other nearby galaxies, GRB2001415,
located in the Sculptor group of galaxies about 13 million light-years away, is the
most distant magnetar eruption captured to date.
Seen in perspective, it appeared as if the magnetar was trying to communicate its existence
to us from its cosmic loneliness, singing in kilohertz with the force of a billion suns.
The eruption provides crucial information for understanding how magnetic stresses are
generated in and near neutron stars. Magnetars in nearby galaxies will be monitored
continuously to understand this phenomenon better. It will also provide a detailed understanding
of quick radio bursts, which are currently one of the most mysterious phenomena in astronomy.