An international group of scientists succeeded in measuring the characteristics of a flare on a distant magnetar for the first time. The flash or flare was captured accidently in April 2020. It released energy equivalent to that produced by the Sun in 1,00,000 years in just a tenth of a second. The magnetar observed is about 13 million light years away and is located in the direction of the NGC 253, a major galaxy in the sculptor group of galaxies.
Magnetars and their formation
Magnetars are relatively rare objects, with only about 30 having been spotted with \in the Milky Way so far. Magnetars are very difficult to observe when they are silent. It is only during a flare that they could be observed. Magnetars have masses of around 10-25 times the mass of the Sun. During the course of their evolution massive stars eventually collapse and shrink to form very compact objects called neutron stars. A neutron star is the collapsed core of a large star, between 10 and 29 solar masses. Though neutron stars typically have a radius on the order of just 10-20 kilometres, they can have masses of about 1.3 to 2.5 of the mass of the Sun. A subset of these neutron stars are the ‘magnetars’ which possess intense magnetic fields. These are highly dense and have immensely high rotation speeds. The rotational speed could range between 0.3 and 12.0 seconds.
Magnetars have high magnetic fields in the range of 1015 gauss (a unit of magnetic induction, equal to one ten-thousandth of a tesla). They have the power to emit energy in the range between given by luminosities of 1037-1040 joules per second. In comparison to this the luminosity of the Sun is in the order of 1026 joules per second which is a factor of at least 1011 lower.
Eruptions in Magnetars
Eruptions in magnetars may occur due to instabilities in their magnetosphere or to a kind of ‘earthquakes’ of ‘starquakes’ produced in their crust, which is a rigid and elastic layer and has a thickness of about a kilometre. Regardless of the trigger, in the magnetosphere of the star a type of waves will be created. These waves are called the Alfven waves, (a type of magnetohydrodynamic wave in which ions oscillate in response to a restoring force provided by an effective tension on the magnetic field lines). These waves also occur in the Sun. While bouncing back and forth between the points at the base of its lines of magnetic field, these waves interact with each other dissipating energy.
The oscillations detected in the eruption are consistent with the emission produced by the interaction between Alfven waves. The crust quickly absorbs the energy within the Alfven waves. Hence in a few milliseconds the magnetic reconnection process ended. The pulses detected in the GRB2001415 also disappeared after 3.5 milliseconds after the burst.
The analysis of the phenomenon has made it possible to estimate that the volume of the eruption was similar or even greater than that of the neutron star itself. The studying of these flares would not only help in understanding the physics of magnetars, it would also help in understanding fast radio bursts, which are among the most enigmatic phenomenon in astronomy.
The study was published in detail in the international journal ‘Nature’. Six researchers from the University of Valencia, 15 scientists of Spanish origin out of a total of 41 scientists contributed in this research.
The observation was carried out automatically, without any human intervention by the image processing system of the atmosphere-space interactions monitor (ASIM). ASIM instrument is on board the International Space Station. The artificial intelligence system ASIM was developed at the Image Processing Laboratory (IPL) of the University of Valencia, has provided an excellent quality of data. The ASIM was mainly designed with its large effective area to observe terrestrial gamma ray flashes. It is a coincidence that the GRB2001415 was observed by ASIM instrument.
The study is crucial as it would lead to understand about giant magnetar eruptions in a better way.
The scientists found that even in an inactive state, magnetars could be one hundred thousand times more luminous than our Sun. The GRB2001415 magnetar is only the second one to be studied which is located outside the galaxy.
ASIM
ASIM is a European Space Agency (ESA) mission developed by Denmark, Norway, and Spain. It is operational in the International Space Station (ISS) since 2018.
The objective and activity of ASIM is to monitor violent phenomena in the Earth’s atmosphere from Optical to Gamma Rays. It has already detected more than 1000 gamma-ray eruptions. These phenomena are unpredictable. The ASIM is programmed to autonomously decide when something has happened and it sends the data to the different centres of the Science Data Centre in Copenhagen, Bergen, and Valencia.
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